Industrial hydraulics-MANUAL.pdf

Electric Drives and Controls

Hydraulics

Linear Motion and Assembly Technologies

Project Manual Industrial Hydraulics Trainer‘s manual

Pneumatics

Service

RE 00845/04.07

Foreword

Bosch Rexroth AG I RE 00845/04.07

Foreword In July 2004 the Federal Minister for Economics and Labor passed the new regulations for vocational training in industrial metalworking professions. Basic training for the entire field of professions, the structure and objectives of vocational training are set out in paragraph § 3. Skills and knowledge (qualifications) are to be imparted with reference to practical needs. To be capable of carrying out qualified work, the trainees are to be trained in particular in independent planning, execution and checking as well as acting in the overall operative context. Specialist qualification Core qualification

Profession-specific specialist qualifications, e.g. the manufacture, assembly and disassembly of assemblies and systems are to imparted in conjunction with core qualifications, e.g. planning and organizing of the related work and the evaluation of work results. The training contents for the profession-specific specialist qualification include, among others, business processes and quality assurance systems in the relevant field of activity.

Project Manual

The present Project Manual Industrial Hydraulics is intended as accompanying and exercise book to help trainers and technical instructors to impart knowledge through project work.

BIBB

In line with the exercises compiled by the Bundesinstitut for berufliche Bildung in Berlin BIBB (Federal Institute for Vocational Training in Berlin BIBB) project tasks are described, which are oriented towards the restructured industrial metalworking and electrical engineering professions.

Practice-oriented project tasks

With all practice-oriented project tasks core and specialist qualifications are imparted in an integrated form involving independent planning, execution and checks. The training course was structured in a way that the project manager/trainer explains the project order first and also supports the trainees during their project work. In the course of the further project tasks, the information and assistance provided by the project manager is reduced. In this way the trainees learn to actively proceed in line with project management requirements.

Foreword

Notes


Introduction


Restructuring of industrial metalworking and electrical professions The increasing importance of process-oriented working procedures, the growing complexity and networking of new technologies as well as comprehensive, customer-oriented services have resulted in the necessity to restructure industrial metalworking professions, which was laid down in regulations in 1987.

1987

2004

3,5

3,5

2

Subject area-specific specialized training

Training period (years)

Subject area-specific specialized training

3

Profession-specific specialized training

1

Interdisciplinary specialized training Basic training

3

2

Profession-specific specialized training over 21 months, including specialized task in the company’s field of activities

Integrated training 1

0

Common core qualification 21 months

0

Restructuring of industrial metalworking professions (source: DIHK 06/2004)

Qualification requirements The requirements for core qualification are met by solving tasks set in the form of project steps, which involve informing, planning, decision-making, executing, checking and assessing. Mastering and internalizing the multitude of qualifications finally results in the professional competence to act.

Time frame - method (source: DIHT 06/2004)

ns at io

Synthesis of qualification contents

al

ns

qu

ifi ca tio

ist ia l ec

al qu re

- Core qualifications - Specialist qualifications + Fields of activities

Sp

→ Training pattern (technical structure)

2nd step

ifi c

Analysis of qualification requirements

Co

1st step

Field of activities

→ Time frame (time structure) In the sense of fields of work/activities within the context of professionspecific business processes

Introduction


Imparting knowledge through project work The present Project Manual Industrial Hydraulics is intended for imparting the required specialist knowledge in the field of hydraulic control technology in practice-oriented applications. Through the logically structured project work the trainee: Training contents

• is to understand the physical laws and technical interrelationships (area, pressure, force, work and power), • is to become able to explain the function, structure, practical operating principle and possible applications of hydraulic equipment, • is to become able to read and understand symbols and circuit diagrams, • is to get to know basic controls of hydraulics and assemble units according to prepared circuit diagrams, • is to be made familiar with types, properties, requirements and application of hydraulic fluids.

Framework curriculum

The project tasks and project work described in the Project Manual Industrial Hydraulics provide trainers and trainees with information and instruments that will help them comply with the demands made on the transfer of specialist know-how in the field of hydraulics. The sub-objectives listed below, which are taken from the framework curriculum for vocational training of industrial mechanics, are matched with the regulations for vocational training in industrial metalworking professions dated 09.07.2004 (BGBl. I. S. 1502). The sub-objectives listed refer to training objectives given for hydraulic control technology. Industrial mechanics • plan and organize work sequences, check and assess work results, • verify mechanical and physical variables, • assemble and disassemble machines, equipment, fixtures and systems, • commission systems and plants, including open and closed-loop control equipment, and instruct customers, • carry out maintenance work and ensure the operability of technical systems, • prepare technical documentation, • apply standards and regulations for safeguarding the process and product quality and contribute to continuing improvements in the work sequences in the company.

Fields of activities

Industrial mechanics are mainly assigned to professional activities in the field of production, assembly, maintenance and automation of technical systems. The fields of activities mentioned before are dealt with in individual training sections. Within the fields of activities, the training sections of the individual training years are based on each other.

Training sections

In training section-oriented lessons the solutions required for project handling are not imparted like in conventional lessons. The solution of the task set is worked out alternately in systematic, technical and situation- or case-related training. In the course of the project work it should be envisaged that the trainee can handle the projects on his/her own and under his/her own responsibility and, whenever possible, in a team. This brings the training contents closer to the trainee's real world of experience, which enables and simplifies imparting the professional competence to act in the lessons. To solve a more complex project task, it may be required to impart the basic principles for this project in systematic technical training.

Introduction


Training section 6, which is geared to hydraulic control technology, is described below. (Training framework curriculum § 10 section 1 No. 10/Control technology) Training section 6:

Installing and commissioning control systems

2nd year of training Recommended time: 60 hours

The trainees are to install and commission control systems. They determine the control components to be used and the functional sequence for controls on the basis of circuit diagrams and other documentation for various component technologies. For this, they use manufacturers's documents. The trainees plan and realize the set-up of the control. They commission the control system observing rules for safety at work. They develop strategies for troubleshooting and optimization of the control systems and apply them. They document and present their results utilizing suitable user programs. Contents: • Technology diagram • Hydraulic power part • Supply unit • Sensors • Flow of material, energy, information • Electrical circuit diagrams • Pressure fluids • Pressures, forces, velocity, flow • Operating modes • Plant safety

Training schedule

The starting point of didactic-methodical structuring of the training situation in the individual training sections is to be the business and work process in the vocational field of activities. This is reflected in the formulation of objectives in the individual training sections. The objectives of the training sections are the decisive factors for the structuring of the lessons and represent the minimum scope together with supplementary contents. The technical contents of the individual training sections are formulated generally and are not listed in a differentiated way. The individual contents of the training sections are coordinated with the training curriculum for in-company training. According to § 7 of the regulations for vocational training in industrial metalworking professions deviations from the training curriculum are permitted in terms of technical contents and time schedule, in particular, where practical requirements necessitate this deviation. The project tasks described in the Project Manual Hydraulics are structured so that the trainee achieves the training objectives described in the project definition in 6 project steps: • Informing, • Planning, • Deciding, • Executing, • Checking, • Evaluating.

Introduction


Specialist competence

The objectives described are geared to the development of competence to act. The trainee will develop his or her competence to act from the capability and willingness to solve tasks and problems and evaluate results in a target-oriented manner, skillfully, methodically and independently on the basis of technical knowledge and skills.

Professional competence to act

The projects described in the project definition are oriented towards practical needs and are characterized by a high level of conformity with customer orders from industry and trade. Customer orders represent complete activities and develop and promote the trainee's professional competence. As mentioned before, the trainee is to work off the project task or the project order in 6 steps. 1. Informing Based on the project definition, the trainee is to get a clear idea of the finished solution, including any required details. This is achieved through a systematic analysis of the project documentation and, if required, by asking questions. Possible questions:

• What is to be done? • Have I understood the task completely? • Which hydraulic component/system is to be dealt with?

2. Planning Planning means the theoretical preparation and anticipation of the concrete execution. In detail, planning requires competence to handle the project order and to organize the project handling steps. Possible questions:

• • • •

How to proceed? What knowledge is required? Which aids are available? Are there comparable applications in my company?

3. Decision-making After the planning stage, the trainee determines the aids to be used, e.g. which data sheets are required for coping with the project task. He/she decides on the sequence and the interrelationships of the individual project steps. Moreover, a decision should be made as to whether it would be easier to solve the project task in a team. Possible questions: • Which hydraulic components will be used? • How can you know that technical data sheets are up to date? • Have I utilized all available sources of information? • Are the prescribed safety instructions at hand? 4. Executing: The order is to be executed according to the work instructions given in the chapter "order execution", taking all safety notes into account. After a thorough preparatory phase, the trainee is to carry out the project order largely on his/her own. After the solution was worked out in writing, it should be verified or questioned, whether the right attempt at a solution was selected. Depending on the project order, the possibilities of execution may be limited. This is valid, for example, in the case of costly work in the field of information technology. Possible questions:

• Have I chosen the correct sequence?

5. Checking: The trainee must check intermediate results as early as during the execution stage, and finally the result of the customer requirement. In some cases, the result can be compared with the manufacturer's documents. In the case of measuring exercises, it must be checked, whether the measured results are realistic. The documentation should also be finally corrected, improved and completed. This also includes the preparation of a final report. After completion, the trainer makes a final check.

Introduction

Possible questions:

• • • • •


Was the control properly installed? Has the project objective been complied with? Is the customer satisfied with the project result? Which documentation is required? Is the result completely documented in the correct order?

6. Evaluating: In the final evaluation phase, an external or self-evaluation is to be carried out on the basis of a comparison of project order documents, the installed control and results of measurements and checks. Faults, if any, and their causes must be analyzed and possibilities discussed as to how faults can be avoided in the future. The trainee must learn to assess his/her strengths and weaknesses and develop objective quality standards for his/her acting, which ultimately leads to personal competence. The evaluation can be finalized in a technical discussion, possibly also in a discussion with the customer. General notes: For didactic reasons, we refer exclusively to trainees and trainers in the present manual. We expressly point out that these terms include all persons involved in the basic and advanced training: Instructors, teachers, project managers, etc., whether male or female. Procedural knowledge

In this manual, we do not give notes on procedural knowledge (explanatory knowledge). It is the knowledge of how to achieve a certain result with which measures, procedures or processes - in this case, how the learning target can be reached. The present manual must be understood as a tool for providing the required core and specialist qualification that must be imparted in an integrated form through independent planning, executing and checking according to the regulations for vocational training in industrial metalworking professions.

Pictogram

The pictograms, which are used as recurrent symbols, are to transfer important information as quickly as possible in the form of a simplified graphical representation and independently of languages.

Introduction


Project designation with short description of the industrial application The knowledge of basic principles of hydraulic control technology is to be imparted with relation to practice. The trainer can impart the basic knowledge of hydraulics in 21 individual projects. Together with the customer requirements the detailed project definitions are finally intended to make the function and possible applications of individual system components clear to the trainee during processing of the order. No. Project designation

Industrial application (example)

01

Hydraulic power unit

Pressure oil supply to a hydraulic cylinder by a hydraulic power unit. Rating of a simple power unit on the basis of parameters specified by the customer.

02

Hydraulic pump, charac- Typical features of a pressure-compensated vane pump. teristic curve Understanding the control behavior with the help of a characteristic curve.

03

Single-rod cylinder, pressure intensification

Safety aspects when using a single-rod cylinder and a meter-out throttle, e.g. for an advance movement.

04

Single-rod cylinder, flow

Different traversing speeds when extending and retracting a single-rod cylinder. Application of different types of hydraulic cylinders.

05

Hydraulic motor

Powering a hoist with the help of a hydraulic motor for lifting and lowering of a load.

06

4/3 directional valve

Controlling the direction of a single-rod cylinder by means of a 4/3 directional valve. It should be possible to position the cylinder at any position. Properties of different directional valve spool shapes and symbols.

07

Check valve

Protection of a vertical cylinder with suspended load in a welding in a welding fixture by means of a check valve. When a tool change takes place, lowering of the load at adjustable lowering speed by means of a shut-off valve.

08

Check valve, pilot operated

Protection of a vertical cylinder with suspended load by means of a pilot operated check valve. Opening the check valve by means of a 4/2 directional valve, adjustable lowering speed.

09

Throttle valve, adjustable

Powering a conveyor belt by means of a hydraulic motor with adjustable output speeds for both directions.

10

Throttle check valve

Traversing a tool carriage at different speeds.

11

Flow control valve

Rotary drive (hydraulic motor) with constant speed.

12

Pressure relief valve, direct operated

Preparation of a characteristic curve for the pressure/flow relationship. Possible use of direct operated pressure relief valves.

13

Pressure relief valve, controls

Electrical pre-selection of various pressures (series, parallel circuit) on punching equipment.

14

Pressure reducing valve

Swiveling a clamped workpiece by means of a hydraulic motor.

15

Pressure switch

Hydraulic pressing of two workpieces with monitoring by a pressure switch.

Introduction


16

Pressure switch, hysteresis

Working out the hysteresis of a mechanical pressure switch.

17

Hydraulic accumulator

Moving the tool from the working range of the machine tool using the oil volume stored in the hydraulic accumulator.

18

Regenerative circuit

Increasing the velocity by using the oil returning from the single-rod cylinder for extending.

19

Rapid speed/creep speed Rapid speed/creep speed control for lifting a pallet onto a control conveyor belt at load-independent, adjustable creep speed and with fastest return stroke possible.

20

Valve by-pass control

21

Commissioning, Observing regulations, safety rules and generally recinspection, maintenance, ognized technical rules when handling production and ... hydraulic systems in everyday work.

Lifting and lowering of a load by a single-rod cylinder, which is controlled by a 4/3 directional valve with blocked central position. Sparing of the hydraulic pump and energy savings through by-pass circuit.

Introduction


Comparison of project exercises of Bosch Rexroth AG/BIBB The comparison below refers to the BIBB training course Hydraulics, recommended and published by the Bundesinstitut für Berufsbildung (BIBB).

Project no.

Project designation

Project content

BIBB

01


Component selection for hydraulic power unit

A1

02

Hydraulic variable displacement pump

Pump characteristic curve

A2

03

Single-rod cylinder/pressure

Safety aspects with regard to pressure intensification

B 1.1

04

Single-rod cylinder/flow

Traversing speeds

B 1.2

05

Hydraulic motor

Lifting platform drive

B2

06

4/3 directional valve

Control of direction, single-rod cylinder

B3

07

Check valve

Protection of a hydraulic cylinder, negative load

C1

08

Check valve, pilot operated

Check valve, flow possible from both sides

C1

09


Conveyor belt drive

D1

10


Traversing an advance slide

D3

11

Flow control valve

Tool drive

D2

12

Pressure relief valve

Characteristic curve

Pressure relief valve controls

Pressure pre-selection on punching equipment

E1

14


Tool advance

E3

15

Pressure switch

Workpiece pressing with monitoring

E4

16

Pressure switch hysteresis

Characteristic curve

E4

17

Hydraulic accumulator

Storing energy in view of a hydraulic pump failure

F1

18

Regenerative circuit

Increasing the velocity by using the returning oil flow

G1

19

Rapid speed/creep speed control

Production line, lifting of a pallet

G2

20

Valve circulation control

Lifting and lowering of a load

G3

21

Commissioning

Commissioning, troubleshooting, maintenance

H1

13

E 1.2

Introduction


Component matrix The matrix below provides an overview of the components, which are required for the individual project exercises. Project 01 02 Component designation ZY 1.3 Double-acting cylinders ZY 1.Load Double-acting cylinders with load DM 2.N Hydraulic motor DW 3E 4/2 directional valve C DW 4E 4/3 directional valve G DW 10E 4/3 directional valve J DW 13E 4/3 directional valve E DS 2.1 Check valve DS 1.1 Check valve, pilot operated DZ 2.1 1 Shut-off valve DD 1.1 Pressure relief valve DD 2 Pressure reducing valve DF 1.2 1 Throttle valve DZ 2.2 Throttle check valve DF 3 Flow control valve DD 6.E Pressure switch DZ 3.2 Hydraulic accumulator DE 2 Limit switch DZ 4.1 2 Distributor plate DZ 1.4 1 Pressure gauge/minimess connection DZ 25.1 1 Hydraulic hose/minimess connection

03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21

1

1

1

1 1

1

1

1

1

1 1

1

1

1

1 1

1

1

1

1

1

1 1

1

1

1

1 1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1 1

1

1

1

1

1 1

1

2

1

2

2

2

2

2

1

2

2

1

1

1 1

1

1

1

1

1

1

1

1 1

1 1

1

1

1 1 2

1 3

3

1

1

3

3

2

1

2

1

2

3

1

4

3

3

3

4

3

4

1

3

3

3

4

3

3

3

4

3

4

1

3

3

3

1

1

2

2

1

2

3

3

3

4

1

1

3

3

3

4

Note on the utilization of the matrix: • The table shows the number of hydraulic components required for each exercise. • Optionally, the following is required additionally: – 1 stopwatch for projects 02, 04 and 05 – 1 flowmeter DZ 30.N for projects 04 and 06 – 1 tachometer in project 05 and – 1 Multihandy (electronic measuring transducer) 5050 for acquiring the values of the flowmeter (measuring turbine) and the tachometer.

Introduction

10


Overview of components Symbol

Component designation

Type designation

Double-acting cylinder with single-sided piston rod

ZY 1.3

Double-acting cylinder with single-sided piston rod with load

ZY 1.Load

Fixed displacement motor with external leakage line and two directions of rotation

DM 2.N t

4/2 directional valve with solenoid actuation, spring return

DW 3E

4/3 directional valve with direct actuation by two solenoids, spring centering of the central position and central position P - T, A, B

DW 4E

4/3 directional valve with direct actuation by two solenoids, spring centering of the central position and central position P, A -B-T

DW 10E

4/3 directional valve with direct actuation by two solenoids, spring centering of the central position and central position P, T, A, B

DW 13E

Check valve with spring, flow possible in only one direction, rest position closed, cracking pressure 1 bar

DS 2.1

Pilot operated check valve, with spring, pilot pressure enables flow in both directions

DS 1.1

Shut-off valve, actuated by turning

DZ 2.1

Direct operated pressure relief valve, the cracking pressure can be adjusted by means of a spring

DD 1.1

Introduction

11


3-way pressure reducing valve

DD 2

Pressure switch, electromechanical, adjustable

DD 6E


DF 1.2

Throttle check valve, adjustable, free flow in one direction

DZ 2.2

2-way flow control valve, adjustable, for one direction of flow, largely independent of viscosity and pressure differential, adjustable, with by-pass check valve

DF 3

Accumulator safety block for diaphragm-type accumulator

DZ 3.2

Pressure gauge with hose and quick release coupling without check valve

DZ 1.4

Hose with quick release coupling with check valve

DZ 25.1

Hose

VSK 1

Introduction

12


Distributor plate with four ports

DZ 4.1

Flow-meter

DZ 30

Tachometer 1)

red black

Limit switch, inductive

blue 1)

Stopwatch

1)

No symbol according to DIN ISO 1219

DE 2.2

Introduction

13


Safety aspects Safety and the economic use of resources are essential demands that are placed on modern plant and machinery and serve to protect people. These two requirements have in common that they have to be taken into account as early as possible, that is, at the product concept stage. Only in this way can optimized and low-priced solutions be found. Safe machines with low consumption demonstrate that the manufacturer masters his processes; they are a quality feature. In order that hazards to plant and machinery can be recognized, safety regulations, product information brochures and operating instructions must be observed. Corresponding notes on the handling of electrohydraulic components and systems of Bosch Rexroth can be found in: • General product information on hydraulic products RE 07008/02.05 • Operating instructions for hydraulic systems AB 01-01.02 • Hydraulic cylinders of tie rod/mill-type design (operating instructions) RE 07100-B/10.04 • Operating instructions DS4 – 1X RE 00225-B/05.05 The safety notes and product information in the above documentation are exclusively valid for Bosch Rexroth hydraulic products. Only when operating instructions, safety notes and product information are observed can the trouble-free operation of Rexroth products be ensured. The present Project Manual Industrial Hydraulics includes warning notes, which precede instructions for activities that involve a risk of personal injury or damage to property. The described precautions for averting risks must be taken.

Conventions This symbol refers to imminent danger that, if not avoided, can lead to severest injuries or death. Warning This symbol refers to a potential risk, which can lead to light or serious injuries or damage to property. Caution

This symbol refers to supplementary information.

Note: The electrohydraulic components and systems described in this Project Manual are technical equipment, which is not intended for private use. The use for the intended purpose also includes that the safety regulations, product information and operating instructions described in the following are read and understood.

Introduction

Qualification of personnel

14


Installation, commissioning and operation, disassembly, upkeep and maintenance require fundamental knowledge of mechanics and electrohydraulics as well as the knowledge of related technical terms. In order to ensure operational safety, these activities may only be carried out by a corresponding specialist or by an instructed person under the supervision of a specialist. A specialist is, who, due to his/her professional training, his/her knowledge and experience and the knowledge of relevant regulations, can asses the duties assigned to him/her, recognize potential risks and take suitable precautions. A specialist must observe relevant technical rules. Consequently, this means that the trainer must point out potential risks to the trainees and provide information on how to avert such risks.

Warning

Liability

Work carried out improperly on electrohydraulic components and systems involves the risk of injury and represents a safety risk during operation of the system, including danger to life!

In the case of damage resulting from improper use and unauthorized interventions, which are not provided in the Project Manual Industrial Hydraulics, any liability claims for defects or other liability claims vis-à-vis Bosch Rexroth AG become void. If Projects 01 to 21 described in the Project Manual Industrial Hydraulics are carried out on training stands and with electrohydraulic components that were not delivered by Rexroth, that is, products of competitors' make, any defect or liability claims vis-à-vis Bosch Rexroth AG shall be void as well. When using competitors' products, observe the safety notes of the manufacturer and make sure that the components and systems comply with currently valid EU Directives. For this reason, commissioning is prohibited until it was established that the electrohydraulic components and systems to be used meet the stipulations Warning

of all relevant EU Directives.

Note: The required safety regulations, product information documents* and operating instructions must be handed over or be accessible to the trainee in their latest issue. In the Project Manual Industrial Hydraulics we do not refer in detail to the correct handling of hydraulic fluids in the project exercises 01 to 21. The corresponding information can be found in the safety data sheet. The correct handling of hydraulic fluids and possible risks as well as measures for averting risks are described in a separate topic "Hydraulic fluids" in the following. * Rexroth product information sheets are valid exclusively for hydraulic products, which are operated with hydraulic fluids based on mineral oil, unless the use of other hydraulic fluids is expressly permitted in the operating instructions.

Basic principles of hydraulics


Basic principles of hydraulics Introduction

Hydraulics, derived from the Greek word hydro = water, refers, in a scientific sense, to the science of still and moving fluids (hydrostatics and hydrodynamics). If we speak of hydraulics in mechanical, vehicle and aircraft engineering, we understand by this the practical application of this discipline of physics in the fields of power transmission and open and closed-loop control technology.

Comparison of systems

System technologies such as hydraulics, pneumatics, electrics/electronics and mechanics compete with each other as means for the transmission of power; on the other hand, they complement each other and are also combined. The decision in favor of a certain system, or a combination, requires detailed knowledge of the features and also of the pros and cons.

Source of energy (drive)

Hydraulics

Pneumatics

Electrics

Mechanics

El. motor

El. motor

Mains

El. motor

Combustion engine

Combustion engine

Battery

Combustion engine

Pressure vessel

Weight Tension force by spring

Energy transmission elements

Pipes and hoses

Pipes and hoses

Electric cables

Mechanical parts: Levers, shafts, etc.

Magnetic field Energy carriers

Fluids

Air

Electrons

Rigid and elastic bodies

Force density (power density)

High

Relatively low

Low

High

High pressures

Low pressures

cf. power/weight ratio of el. motor to hydraulic motor 1:10

Volume and assignment of required installation space is often less favorable than with hydraulics

Good via pressure and flow

Good to excellent

Poor

Large forces Small installation space requirement Smooth control (accelerating, decelerating)

Excellent via pressure and flow

Motion types of drives

Linear and rotary movements can easily be achieved with hydraulic cylinders and hydraulic motors

Electrical open and closed-loop control

Comparison of system technologies

Linear and rotary movements can easily be achieved with pneumatic cylinders and pneumatic motors

Mainly rotary movements

Linear and rotary movements



System planning

The specific advantages of hydraulic technology over other technologies such as pneumatics, electrics and mechanics, can only be utilized to the full extent, if the system planner knows the typical features offered by hydraulic control technology.

Features of hydraulic systems

• Transmission of large forces within a minimum of space; • High energy density • Storing of energy is possible • Stepless changes in motion variables such as velocities, forces and moments • Good monitorability of occurring forces • Swift reversing operation due to small masses (low moments of inertia) of the drive elements • High switching dynamics • Good transmission ratio • Simple conversion of rotary movements into linear movements or vice versa • Constructive flexibility in the arrangement of components • Physical separation of input and output through pipes and hoses • Possibility of automating all types of movements and auxiliary movements by means of pilot control valves and electronic command transmission • Usability of standard components and assemblies • Simple overload protection • Low wear, since hydraulic components are lubricated by the operating medium • Long service life • Possibility of energy recovery

• Pressure and flow losses (fluidic friction) in line systems and control elements • Dependence of viscosity of the hydraulic fluid on temperature and pressure • Leakage problems; therefore risk of accidents and risk of fire • Compressibility of the hydraulic fluid


Energy conversion


Hydraulic systems convert mechanical energy into hydraulic energy, transport it in this form in an open or closed-loop controlled way and then re-convert it into mechanical energy. For the conversion of energy, hydraulic pumps are used on the primary side, and hydraulic cylinders and hydraulic motors on the secondary side. Hydraulic energy and hence the transmitted power can be influenced in pressure and flow by hydraulic pumps, and in its magnitude and direction of action by open and closed-loop control valves. The hydraulic fluid that is directed via pipes, hoses and bores in control blocks or manifolds assumes, among others, the energy transport. For storing and maintaining the hydraulic fluid, additional equipment such as reservoirs, filters, coolers, heaters, measuring and testing instruments are required.

Drive

Electric motor, combustion engine, manual drive

Hydraulic system

Drive

Energy conversion

Open, closedloop control

Energy conversion

Hydraulic pump

Hydraulic open and closed-loop control valves

Hydraulic cylinder, hydraulic motor

Electric energy, thermal energy, mechanical energy

Hydraulic energy

Working element to be actuated

Mechanical energy

Energy conversion in a hydraulic system

As illustrated in the schematic above, an oil-hydraulic system firstly converts mechanical energy into hydraulic energy, transports it in an open or closed-loop controlled way, and then converts it into mechanical work. The components used in hydraulics can be classified according to their function.



The figure below schematically shows the components of a simple hydraulic system.

Hydraulic cylinder


Directional valve

Check valve


Return line filter Hydraulic pump

Section circuit diagram of a hydraulic system



Instead of sectional drawings, standardized symbols according to DIN ISO 1219 part 1 are used in hydraulic circuit diagrams. More detailed information is provided in the next chapter "Symbols".

Symbol circuit diagram of a hydraulic circuit



Symbols according to DIN ISO 1219-1 In fluid power systems, energy is transported within a circuit by a pressurized medium (liquid or gaseous) and open or closed-loop controlled. Graphical symbols help to identify the function in circuit diagrams of fluid power technology. They can also be attached to the components themselves for this purpose. DIN ISO 1219-1

The symbols included in standard DIN ISO 1219 should preferably be used, but their use does in no way rule out the use of symbols commonly applied in other technical areas for identifying pipes and hoses. The followings lists are not complete, but must be regarded as working aid for the preparation or completion of project-related circuit diagrams. The graphical symbols used in the manual comply with DIN ISO 1219 - fluid power technology; graphical symbols and circuit diagrams; part 1: Graphical symbols.

DIN ISO 1219-2

Basic symbols

The basic rules for the preparation of hydraulic circuit diagrams are determined in part 2 of standard DIN ISO 1219. Circuit diagrams are a tool to simplify the planning and description of a hydraulic system in order to prevent - through a standardized representation - uncertainties and faults at the planning stage, during production, installation, and servicing.

Supply line, return flow line, frames for components and symbols Internal and external pilot line, leakage line, flushing line, venting line The crossing of two lines without connection point indicates that there is no connection The connection of two lines is represented by means of a connection point. Hose Function unit for valves having a maximum of four service ports Frame for energy conversion unit (pump, compressor, motor)

Adjustability of a pump/motor

Direction of action of the hydraulic force


Overview of symbols


Directional valves

Pressure control valves

Flow control valves

Check valve


Throttle valve/orifice

Directional poppet valve


Two-way flow control valve

Directional spool valve

Sequencing valve

Overview of symbols according to DIN ISO 1219, part 1 (excerpt)


Hydraulic circuit systems


In the field of hydraulics, we differentiate between three circuit systems: • Open circuit, • closed circuit, • semi-closed circuit.

Open circuit

In an open circuit, the hydraulic pumps usually aspires hydraulic fluid through the suction pipe, which is installed below fluid level. The hydraulic fluid is directed by directional valves to the actuator and fed back to the storage reservoir; this means, there is no connection between the suction pipe of the hydraulic pump and the hydraulic fluid returning from the actuator. Typical features of the open circuit: • The hydraulic pump aspires oil directly from the hydraulic tank, • the hydraulic fluid flows via control elements to the actuator, • the hydraulic fluid flows from the actuator back to the hydraulic tank, • simple structure, • better cooling, • contamination can settle in the hydraulic tank, • large amount of fluid, • large hydraulic tank required, • large space requirement, • unfavorable volumetric efficiency Input speed n = constant

Schematic diagram Lifting speed v = constant

Flow qV = constant

The open circuit is employed, for example, in machine tools, handling systems, press controls, winch drives, and gears for mobile applications. The actuators can be hydraulic cylinders and hydraulic motors.


Closed circuit


In a closed circuit, the hydraulic fluid returning from the actuator is directly re-fed to the hydraulic pump. The high-pressure side of the system is protected by a pressure relief valve. The pressure is unloaded to the low-pressure side, that is, the hydraulic fluid remains in the circuit. The design-inherent permanent, internal leakage of the hydraulic pump and the hydraulic motor is compensated for by a separate auxiliary pump, which is flange-mounted to the hydraulic pump in most of the cases. Typical features of the closed circuit are: • The hydraulic fluid is fed by the pump to the actuator, • the hydraulic fluid flows from the actuator directly back to the pump, • compact design, • silent, smooth running, • good controllability, • good volumetric efficiency, • complicated structure, • greater stressing of the oil, • sensitive to contamination

Schematic diagram

Auxiliary pump for leakage compensation

Flow qV = variable Output speed n = variable

Cooler

The closed circuit is used almost exclusively in mobile applications, e.g. for powering a wheel loader travel drive. The hydraulic pumps and hydraulic motors used are in most of the cases axial piston units.


10


Semi-closed circuit

The semi-closed circuit is a combination of the open and the closed circuit and is used, if the volume must be balanced by means of anti-cavitation valves, for example, when a single-rod cylinder is employed in a mobile machine.

drive and control

The schematic illustration "drive and control / driving - controlling - and moving" on the next page shows the task set to a hydraulic cylinder or hydraulic motor as machine element. • The travel speed of the actuator is realized by the hydraulic pump flow. • The direction, start and stop are controlled by directional valves. • The required force can be varied by adjustable pressure control valves. • The specified travel speed of the actuator can be influenced by means of a flow control valve. • Optimized system technology includes monitoring elements such as pressure switches and pressure gauges. Hydraulic accumulators can be provided for realizing faster movements. Heat exchangers optimize the oil quality and hence the availability of the system.


11


drive and control *

driving, controlling and moving * Rexroth-specific statement

Driving machines and systems

Hydraulic cylinders and motors as machine elements

Driving and controlling hydraulic cylinders and motors

Flow

Pumps + storage tank Hydraulic fluids

Direction + position are to be controlled

Start – direction – stop

Directional seat valves Spool, poppet and isolator valves

The required force is to be adjustable

Pressure

Pressure control valves limit – reduce – switch

The required velocity is to be adjustable

Velocity

Flow control valves Throttles – orifices

System technology optimized to suit the specific application Demands made on hydraulic cylinders / motors as drive elements

Power units & accessories – accumulators – pressure switches – pressure gauges – heat exchangers


12


Physical basic principles Pascal's law

Pressure (p) in the vessel results from force (F), which acts on the piston. This means that a greater force (load) generates a higher pressure, whereas with decreasing force (load), the pressure falls. The second relationship lies in the size of the area (A), onto which the force acts. The smaller the area, the higher the pressure; and, of course, vice versa, the greater the area, the smaller the pressure. Consequently, the pressure is dependent on the amount of the effective force (F) and the size of the area (A) onto which this force acts. Pascal's law:

p=

F A

or:

A=

F p

F = pA Force = pressure • area F

p

A

Pascal is the SI unit of pressure. It was named after Blaise Pascal. 1 Pa =

1 kg m • s

2

= 1 N/m2

The force in Newton per surface area of one square meter, where: 1 bar = 100,000 Pascal (105 Pa) 1 bar = 10 N/cm2 In pressure calculations, the unit Dekapascal (daPa) is often used, where one Dekapascal corresponds to 0.1 mbar. 100 Pa = 10 daPa = 1 haPa = 1 mbar 100,000 Pa = 0.1 MPa = 1 bar = 1,000 mbar 1.000.000 Pa = 1 MPa = 10 bar = 1 N/m2


Force transmission

13


In a closed system with two cylinders of different size, only one pressure (p) can prevail. If both cylinders are to be held in balance and the areas (A1 - A2) have different sizes, the loads (F) acting on the areas must consequently be different. Cylinder 1 means:

p=

F1

Cylinder 2 means:

p=

F2

A1 A2 F1

If p is identical in both cylinders, this means:

F1 

Rearranged by force: A2 A1

=

A1

F2 A2

A2 = F2 A1

is the area ratio of the cylinders and is identified by letter ϕ.

Consequently:

Example: Area A1 Area A2 Weight force F1 Weight force F2

F1 • ϕ = F2

Solution:

= 50 cm2 = 750 cm2 = 1.000 daN = ?

F1 

750 cm2

1.000 daN  or with ϕ =

A2 = F2 A1

50 cm2 A2 A1

=

= 15.000 daN

750 = 15 50

F1 • ϕ = F2 1.000 daN  15 = 15.000 daN This means that cylinder 1 with a force of 1,000 daN, which corresponds to a mass of 1,000 kg, can hold cylinder 2 with a load of 15,000 kg or 15 t.

F1

F2

A1

A2


Pressure intensification

14


The extending speed of a piston is to be adjustable by means of a meter-out throttle. Which risk arises, when the throttle is completely closed, e.g. due to dirt? Example: pK = 100 bar ϕ = 2 : 1

ϕ=

AK AR

Solution: pK  ϕ = pR 2 100 bar  = 200 bar 1 pR = 200 bar

Conclusion: Meter-out throttling involves the risk of pressure intensification!

ASt

AK

pK

pR

AR


Flow

15


The flow is the amount of fluid (nominal volume) that moves in a hydraulic systems within a certain time. In conjunction with pumps, we also speak of displacement. The unit commonly used in industrial hydraulics is l/min. If in the schematic diagram below the lever of the pump is shifted to the right, the piston displaces fluid into the system. If there is no counterforce (counterpressure), almost no pressure will consequently build up in the pump. The fluid is fed to the system at zero pressure. Only when the displacement is opposed by a resistance (directional valve, throttle, cylinder piston or similar elements), can a counterforce be generated. The pump continues to displace fluid and compresses the fluid. Pressure builds up, which depends on the resistance not generated by the pump. The pump only displaces fluid into the system.

qV in l/min

t in

s

s in mm A in cm2

qV in l/min V As = t t qV = A  v  6 in l/min

qV =

A in cm2 s v = = Velocity in m/s t s in mm A in cm2 v in m/s In technical data sheets, the size of the pump is given in cm3/revolution. The following formula is applied for determining the power: qV =

Vg  n 1.000

in l/min

Vg = displacement in cm3/rev n = speed of the pump shaft in min-1 (rule of thumb without consideration of the volumetric efficiency).


Flow law

16


The identical volumes flow through a pipe with different cross-sections within the same time. This means that the flow velocity of the fluid must increase at the narrow point.

Flow q is fluid volume V divided by time t

qV =

V t

Fluid volume V is the product from area A times distance s If A • s is subsituted for V, q is then given by

qV =

Distance s divided by time t provides velocity v

V=A•s

As t

v=

s t

Flow q hence equals the product from the cross-sectional area of pipe A multiplied by the velocity of the fluid v qv = A • v.

Flow

Flow q in L/min is the same at any point in a pipe. If the pipe has two cross-sections A1 and A2, corresponding velocities must occur at the two cross-sections.

q1 = q2

q1 = A1 • v1

q2 = A2 • v2

This results in the following continuity equation A1 • v1 = A v 2 = v1 1 > v1 A2

A2 • v2


17


Hydraulic fluids General

In a hydraulic system, the fluid assumes the task of force transmission. This means that certain demands must be placed on the fluid. The fluid should: – be incompressible for the transmission of forces – dissipate heat that is generated – not change its viscosity at different temperatures – carry away abrasion from hydraulic components – be easy to filter – be neutral against metal guides, seals and paints – feature good lubrication properties – be resistant to aging – not be detrimental to health – be easy to dispose of after use

Environmentally friendly Neutral against seals, plastics, paint Corrosion protection Good lubrication properties Good dirt transportation capacity

Temperature stability

Resistant to aging

Demands made on hydraulic fluids

Not detrimental to health No tendency towards foaming Good air separation capacity

Neutral against bearings, good shear stability


18


Requirements of the market

None of the fluids offered on the market today can meet all of the requirements listed on the previous page. Even in view of ongoing discussions about environmental compatibility of hydraulic fluids and in spite of all concerns, mineral oil is still the most common hydraulic fluid used in hydraulic systems.

Selection criteria

Being an important design element and machine element, the hydraulic fluid must be taken into account at the planning stage, and during engineering and commissioning of hydraulic systems. The hydraulic fluid to be used is selected according to the prevailing operating conditions such as: • Operating temperature range • Concept of the hydraulic system • Hydraulic pump type • Working pressure and environmental requirements • Operating time and availability • Economic and ecological factors

Viscosity

Viscosity is the most important criterion for the selection of the hydraulic fluid. Viscosity data indicate whether a pressure medium is light or viscous at a certain temperature and hence whether friction between the fluid layers is smaller or greater. The viscosity is measured in the SI unit mm2/sec. It changes as temperature changes. In a diagram with a double logarithmic scale for the viscosity axis, the representation in the change in viscosity in dependence upon temperature T shows a straight line.

Manufacturer's data

For determining the application limits of a hydraulic system and consequently for the selection of the hydraulic fluid, it is important to take minimum and maximum viscosity values into account that are given by the manufacturer in his documentation for the hydraulic components used. The component manufacturer Rexroth, for example, indicates the data for the selection of the hydraulic fluid in the technical data sheet of the component - RE data sheet - in the section Technical data, hydraulic. Here, you can find details about the hydraulic fluid, hydraulic fluid temperature and viscosity range.


19


Classification of hydraulic oils

Hydraulic oils

Hydro-kinetic application

DIN 51 502

ISO 6743/4

ATF

HA HN

Hydrostatic application

Mobile hydraulics: UTTO, STOU

Hydraulic oils based on mineral oils

Flame-retardant hydraulic oils

Fast bio-degradable hydraulic oils

Hydraulic oils compatible with foodstuffs

DIN 51 502, ISO 6743/4

7. Lux. report, ISO 6743/4, ISO/CD 12922, DIN 51 502, Factory Mutual - USA

VDMA sheet 24568, ISO 6743/4 and ISO 15380

FDA, USDA and NSF classification

DIN 51 524

ISO/DIS 11158

Containing water

HL HLP HLPD HVLP HVLPD

HH HL HM HR HV HS HG

HFAE HFAS HFB HFC

Source: Specialist magazine 0 + P

Water-free

HFDR HFDU

Waterinsoluble

Watersoluble

HETG HEES HEPR

HEPG

HSF H1

NSF H2

Basis white oil

Basis white oil

Basis PAO

Basis PAO Basis mineral oil


20


Classification of hydraulic fluids based on mineral oil

Code letter according to DIN 51 502 and ISO 6743/4

Class L: Lubricants, industrial oils and related products; Class H: Hydraulic systems Code letter (symbol) DIN

Code letter (symbol) ISO-L

Composition Typical properties

Field of application Operating temperature

HH

Mineral oils without active additives (base oils)

Hydraulic systems without specific requirements (only in rare applications today) -10 to 90 °C

HL

Mineral oils with active additives to increase the resistance to aging and to improve corrosion protection

Hydrostatic drives with high thermal stress, good water separation capacity -10 to 90 °C

HM

Mineral oils of type HL with active additives to improve wear protection in the mixed friction area

Hydrostatic drives with high thermal stress, which require additives for the reduction of wear, good water separation capacity -20 to 90 °C

--

HR

Mineral oils of type HL with active additives to improve viscosity / temperature characteristics

Extended operating temperature range when compared with HL oils -35 to 120 °C

HVLP

HV

Mineral oils of type HM with active additives to improve viscosity / temperature characteristics

Among others, hydrostatic drives in mobile hydraulics -35 to 120 °C

--

HS

Synthetic fluids without specific flame-retardant properties

Special applications in hydrostatic systems -35 to 120 °C

HG

Mineral oils of type HM with active additives to improve stick-slip characteristics

Hydrostatic systems with plain bearings at intermittent, low velocities -30 to 120 °C

--

Mineral oils of type HM with detergent / dispersive (DD) additives; DD additives reduce friction values

Hydrostatic drives with high thermal stress, which require EP/AW additives; DD additives hold contaminations in balance, e.g. in machine tools and mobile systems.

--

HL

HLP

(HLPD)

HLPD



21


Classification of flame-retardant hydraulic fluids and water-free, fast bio-degradable hydraulic fluids Code letter according to Composition 7th Luxemb. report, Typical properties DIN 51 502 and DIN EN ISO 6743/4: April 2002

Field of application Operating temperatures (Notes)

Flame-retardant, water-containing hydraulic fluids HFA-E

Oil-in-water emulsions, mineral oil / Power hydraulics of about 300 bar, for synth. esters example in shield tunneling in the field Concentrate share < 20 % of mining

HFA-S

Mineral oil-free watery solutions of Hydrostatic drives - working pressures chemicals < 160 bar Concentrate share < 20 % 5 to < 55 °C

HFB

Water-in-oil emulsion Share of mineral oil 60 %

For example in British mining 5 to 60 °C

HFC

Watery polymeric solution Water share > 35 %

Hydrostatic drives, industrial and mining hydraulics -20 to 60 °C

Water-free, synthetic, flame-retardant hydraulic fluids

HFD-R

Lubrication and control of steam turSynthetic fluids based on phosphate bines, industrial hydraulics esters, -20 to 150 °C water-free in hydrostatic systems often 10 to 70 °C

HFD-U

Synthetic fluids of other composition Hydrostatic drives, industrial hydraulics (mostly carboxylic acid, polyesters) -35 to 90 °C water-free

Code letter according to VDMA 24568 and ISO 15380

Composition Typical properties

Field of application Operating temperatures (Notes)

Water-free, fast bio-degradable hydraulic fluids HEPG

Polyalkylene glycol Water-soluble

Hydrostatic drives, e.g. ship lock hydraulics -30 to < 90 °C

HETG

Triglycerides (vegetable oils) Not water-soluble

Hydrostatic drives, mobile hydraulics -20 to 70 °C

HEES

Synthetic esters Not water-soluble

Hydrostatic drives, mobile and industrial hydraulics -35 to 90 °C

HEPR

Hydrostatic drives, Polyalpha olefins (synth. hydrocarbons) mobile and industrial hydraulics Not water-soluble -35 to < 80 °C




10.000

Viscosity mm2/s

Viscosity/ temperature diagram

22

1.000

* Max. permitted

* Permitted briefly for cold start (cavitation)

100

Recommended range for continuous operation 36

20

12 10 9 8

0 68 10 G VG V 46 2 O SO 2 G I 3 2 15 V IS VG VG VG O O IS IS

Ideal operating point Reference point for all data

* Min. permitted (lubrication problems)

7

IS

6

O

IS

O

5 4

3,0 -40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90 100

120

140

Temperature °C Reference temperature for ISO viscosity classes

Viscosity/temperature diagram with application limits for hydraulic systems

Viscosity

Comparison of different viscosity classes

Viscosity is the reference for internal friction of the fluid. It is the resistance that material particles put up to the force during mutual shifting.

SAE classes

ISO - VG (DIN 51519)

SAE classes

30

100

68

68 20, 20 W

46

10 W

32

5W

22

49 36 25 16

(15) 10

9


Additives

23


No hydraulic fluid can meet all requirements. Thanks to additives, certain properties of the hydraulic fluid can be optimized to suit the requirements of specific applications. For example: • for improving:

– corrosion protection

– pressure resistance

– resistance to aging

– viscosity/temperature behavior

• for reducing:

– the pour-point

– foaming

– wear


24


Practical notes

Effects of air in the oil

Air can be present in hydraulic oils in the following forms: as dissolved air (invisible), as surface foam (visible), and as undissolved, dispersed air (visible). While dissolved air and minor surface foam hardly show any adverse effects, dispersed air can cause severe problems. Since the oil contains very small air bubbles, which are finely dispersed and can rise to the surface only very slowly, the following troubles can occur: • Uneven or jerky movements of hydraulic spools, vibration in the system due to increased compressibility, changed actuating times of servo-valves • Pump noise • Damage to pumps, lines and seals caused by cavitation • Accelerated aging of the oil • Micro-diesel effect, a form of thermal cracking due to high temperatures in compressed air bubbles

Environmental aspects

Hydraulic systems are closed systems. When hydraulic systems are used properly, hydraulic fluid does therefore not get into the environment. Care must be taken that power units are leak-free and maintenance/repairs are carried out in due time. Especially hydraulic hoses and hose connections must be intensively observed and inspected. Oil changes must be made properly and thoroughly; waste oil must be disposed of in accordance with all relevant legal stipulations.

Safety aspects

Hydraulic fluids based on mineral oil are water-endangering and inflammable. Pressure fluids may only be used, if the corresponding safety data sheet of the manufacturer is at hand and all precautions prescribed therein are observed.

Danger

If leakage on the hydraulic product can lead to the contamination of water and soil, the hydraulic product must be placed in a suitable oil drip tray.


Filters

25


Causes of contamination One of the preconditions for the trouble-free operation of a hydraulic system is filtration of the hydraulic fluid and the ambient air connected to the tank. The contamination to be removed by means of filters enters the hydraulic system from the surroundings via the filling connection or past the seals. This type of contamination is termed external contamination or contamination that enters the system from outside. The contamination ingression rate to be expected depends exclusively on the contamination of the surroundings and the design of systems and components. Moving parts in the hydraulic system such as pumps, spools and valves also generate particles (abrasion). This type of contamination is termed internal contamination. Especially during commissioning of the system, there is a risk that the individual components are damaged or destroyed by solid particles that were transported into the system already during assembly. The majority of malfunctions in hydraulic systems are caused by strongly contaminated hydraulic fluids. Fresh pressure fluid, with which the hydraulic fluid is to be filled, is often contaminated to an impermissibly high level. – Contamination during the production of components (component contamination)

Due to the often highly complicated internal contours of housings and internal parts of components, the latter cannot in every case be sufficiently cleaned. When the hydraulic system is flushed, the contaminants get into the hydraulic fluid. Components are often preserved for intermediate storage. The preservatives bind dirt and dust. This dirt also gets into the hydraulic fluid when the system is commissioned. Typical contaminants are: Chips, sand, dust, fibres, paint flakes, water or preservatives.

– Contamination during the assembly of systems (assembly contamination)

When individual parts are joined, e.g. installation of fittings, solid particles may be produced. Typical contaminants are: Seal material, scales, welding beads, rubber parts from hoses, residues of pickling and flushing fluids, cutting and grinding dust.

– Contamination during operation of the hydraulic systems (production contamination)

Abrasion in components results in the formation of particles. Particles smaller than 15 µm are particularly wear-promoting. Aging residues in hydraulic fluids, which are in most of the cases caused by high operating temperatures, change the tribological properties of the hydraulic fluid.


Critical tolerances for hydraulic components

26


Gear pump J1 from 0.5 to J2 from 0.5 to

5 μm 5 μm

Vane pump J1 from 0.5 to 5 μm J2 from 5 to 20 μm J3 from 30 to 40 μm

Piston pump J1 from 5 to 40 μm J2 from 0.5 to 1 μm J3 from 20 to 40 μm J4 from 1 to 25 μm

Valve J1 from 5 to 25 μm

Servo-valve J1 from 0.5 to 8 μm J2 from 100 to 450 μm J3 from 20 to 80 μm


Causes and sources of contamination

1 2 3 4 5

External contamination Installation + repair Fresh oil Abrasion in the pump Abrasion of seals

27



Arrangement of filters in the open circuit

28


The task of filters is directly related to their arrangement in the system. Filters perform certain tasks depending on their location in the system.

Main flow filtration

Control

1 8

7

10 3

6

2 5 4

1 Built-on return flow filter 2 Filling filter 3 Breather filter 4 Suction filter 5 Hydraulic pump 6 Cooler 7 Hydraulic pump 8 High-pressure filter 9 Off-line filter 10 Underpressure switch

Off-line filtration

9


Filter types

29


Return flow filter These filters are located at the end of the return flow line and are designed mostly as filters for tank mounting. This means that the hydraulic fluid coming from the system is filtered before being fed back to the tank. Thus, the major part of dirt particles, which entered the system or are produced in the system, are filtered out of the hydraulic fluid. The maximum flow must be taken into account for the selection of the filter size. Advantages – Low cost – Ease of maintenance – Can be fitted with clogging indicator – Provides fine filtration – No pump cavitation Disadvantages – A by-pass valve is required – Lets dirt particles through the open by-pass valve in the case of pressure peaks and cold start conditions The filter shown below is mounted to the tank cover using a mounting flange. The housing with the filter connection protrudes directly into the tank. A great advantage of this filter design is good accessibility and consequently maintenance-friendliness. The filter element can be quickly and easily taken out by removing the cover. An important feature is that a strainer encloses the filter element. When the filter element is taken out, the strainer is pulled out as well, thus preventing dirt already settled from flowing into the hydraulic tank. The filters are generally provided with a connection for a clogging indicator.


30


In-line filter (pressure filter) This filter type ensures that the function of downstream hydraulic components is maintained. For this reason, these filters must be installed as closely as possible to the components to be protected. The following aspects are decisive for the use of pressure filters: – Components are particularly susceptible to dirt (e.g. servo-valves or high-response valves) or decisive for the operation of a system. – Components are particularly expensive (e.g. large cylinders, servo-valves, hydraulic motors) and of extreme importance for the safety of a machine. – Downtime costs of a system are extraordinarily high. Pressure filters should generally be fitted with a clogging indicator. Upstream of particularly critical components, only pressure filters without by-pass valve should be used. This type of filter must be provided with a filter element that withstands also higher pressure differential loads without any damage. The filter housings must withstand the max. system pressure. The filter basically consists of a filter head with a screw-in filter housing and a filter element. The standard variant is designed without by-pass valve and without pressure unloading screw. A connection for a clogging indicator is generally provided. Advantages – Can be installed directly upstream of sensitive components – No pump cavitation Disadvantages – Element must be provided for a high differential pressure


31


Filler and breather filter

Symbol for filler and breather filter without (on the left-hand side) and with by-pass valve (on the right-hand side)

Filler and breather filter with and without filling filter

Filler and breather filter with filling strainer

In the past minor importance had been attached to these filters in hydraulic systems. However, according to latest findings, they are one of the most important elements for the filtration of hydraulic fluids in hydraulic systems. A significant part of contaminants gets into hydraulic systems through unsuitable venting equipment. Design measures such as pressurization of oil tanks are often uneconomical when compared with the highly efficient breather filters offered on the market today. Depending on the required cleanliness class, breather filters are equipped with replaceable elements of different filtration ratings. The filters should be fitted with a connection for clogging indicators (2). Filler and breather filters basically consist of an air filter (1) for filtering the air flowing into the tank and a filling strainer (3) for retaining coarse particles when the system is filled with fluid. The air filters are available with different filtration ratings so that CETOP standard RP 70 can be complied with, which prescribes the same filtration rating for system filters and air filters. The requirements for this filter type are laid down in DIN 24557.


Filtration media

32


For the filtration methods described, various filter media or a combination of filter media are used. a) Surface filtration

With surface filters, the particles are separated directly at the surface of the filter media. Particles that get into the filter medium due to their small diameter can pass through the filter without any hindrance. However, the filter resistance increases as the surface is clogged. The filter cake built up on the surface can result in a reduction in the filtration rating.

For surface filtration, diaphragm filters of filter materials made of wire mesh, metal edges or Dutch weave are used.

b) Deep filtration

The fluid to be filtered penetrates the filter structure. The particles to be removed are also retained in the deeper layers of the filter. As more and more particles are retained by the filter, the flow resistance increases so that the filter element has to be replaced. For these filters, filter media are used, which are made of – impregnated cellulose materials (organic filter material), – glass fiber material (inorganic filter material), – sintered metal meshpacks, – porous, sintered metal.


Particle size and filtration rating

33

Finest particle contamination Finest particles (3 to 5 µm) cause an impairment of function and reduction in the performance due to: – the erosive effect of finest particles (often erosion on control lands) – fine sedimentation in narrow gaps (through edge filtration effect - risk of clogging) – Changes of the operating medium (oil aging) as a result of chemical reactions on the particle surface Finest filtration


Fine particle contamination Fine particles (5 to 20 µm) cause cratering mainly in narrow fits. The consequences are: – Increase in clearance due to abrasion (increased internal leakage) – Temporary failure (brief seizing effect on sliding spool valves or leakage on valve seats)

Coarse particle contamination Coarse particles > 20 µm often cause a sudden total failure due to clogging and blocking effects or direct destruction. Typical: – Blocking of nozzles – Jamming or seizing of spools – Material breakouts due to effect of large forces

– Total failure due to severe abrasion

Fine filtration

Effective separation of finest- Partial separation of fine dispersed particles particle contamination and (b3 to 5 → 100) complete separation of coarse-grain contamination High differential pressure(b5 to 20 → 100) stable finest filters safeguard the function Fine filters reliably control the acceptable degree of – They minimize the formacontamination of the system tion and further development of erosion – They protect components optimally against contami– They prevent clogging of nation narrow gaps – They reduce cratering – They provide protection against aging of oil – They prevent sudden failures of components – They prevent system malfunction

Coarse filtration Separation of mainly coarse particles (bX → 100) X = µm particle size, which can cause a sudden failure on the component to be protected. Coarse filters protect the system against coarse particle contamination They reduce the risk of a sudden failure or total loss.


Classification systems for the degree of contamination of the hydraulic fluid

34


The solid particle content in the hydraulic fluid is determined with the help of classification systems (standardized cleanliness classes). The most common standards today are NAS 1638 (National Aerospace Standard) and DIN ISO 4406. Classification according to NAS 1638 14 cleanliness classes are available for the classification of the hydraulic fluid. For each class, a certain number of particles (in 100 ml) is specified for each of the 5 sizes.

Contamination class

Particle size in µm 5 - 15

15 - 25

25 - 50

50 - 100

> 100

00

125

22

4

1

0

0

250

44

8

2

0

1

500

89

16

3

1

2

1000

178

32

6

1

3

2000

356

63

11

2

4

4000

712

126

22

4

5

8000

1425

253

45

8

6

16000

2850

506

90

16

7

32000

5700

1012

180

32

8

64000

11400

2025

360

64

9

128000

22800

4050

720

128

10

256000

45600

8100

1440

256

11

512000

91200

16200

2880

512

12

1024000

182400

32400

5760

1024

Contamination classes to NAS 1638 Maximum number of dirt particles in 100 ml hydraulic fluid


Classification according to ISO DIS 4406 Assignment of scale numbers

35


Number of particles per milliliter more than

Scale number

up to and including

2500000

> 28

1300000

2500000

28

640000

1300000

27

320000

640000

26

160000

320000

25

80000

160000

24

40000

80000

23

20000

40000

22

10000

20000

21

5000

10000

20

2500

5000

19

1300

2500

18

640

1300

17

320

640

16

160

320

15

80

160

14

40

80

13

20

40

12

10

20

11

5

10

10

2.5

5

9

1.3

2.5

8

0.64

1.3

7

0.32

0.64

6

0.16

0.32

5

0.08

0.16

4

0.04

0.08

3

0.02

0.04

2

0.01

0.02

1

0.00

0.01

0


Filter clogging indicators

36


Inside the clogging indicators, each change in pressure is recorded as change in travel by means of metering pistons or diaphragms. A piston with attached magnet is moved against the force of a spring inside the clogging indicator. On visual clogging indicators, a unipolar magnet is mounted in the indicator head. The closer the poles come to each other, the greater becomes the repulsive force between the magnets, until finally the red indictor button pops out. With the electrical variant, a switching contact picks up. For a permanent indication of the element contamination electronic clogging indicators were developed. Through the use of these indicators, maintenance intervals become foreseeable. With these fully electronic clogging indicators, the differential pressure building up as a result of contamination of the element is converted contact-free into an analog electrical output signal with the help of a sensor. A pressure peak suppression and cold start suppression are additionally integrated.

Differential pressure clogging indicators

Backpressure clogging indicators

Safety notes


Fundamental safety notes In order that potential risks for plant and machinery can be recognized, safety regulations, product documentation and operating instructions must be observed. The trainer must make the required documents available to the trainee. When competitors' products are used, the safety notes of the relevant manufacturer are applicable, and it must be ensured that the components and systems comply with currently valid, relevant EU Directives.

Warning

For this reason, commissioning is prohibited until it was established that the electrohydraulic components and systems to be used meet the stipulations of all relevant EU Directives.

Fundamental, general safety notes

Observe

Warning

• danger signs and safety notes on the machine • instructions, which prescribe the behavior during operation in order to prevent accidents and health damage and must be prepared by the operator/employer on the basis of, for example, regulations for the prevention of accidents, • operating instructions, which ensure the proper use of the hydraulic system in accordance with its intended purpose. The operating instructions are intended for information purposes and for the prevention of risks when hydraulic components are being installed in a system - in this case mounting of electrohydraulic components on the training stand -, and include information and notes on transport, storage and maintenance (inspection, servicing, corrective maintenance) of the hydraulic system. Only when the operating instructions are strictly observed can accidents and damage to property be avoided and the trouble-free operation of the hydraulic system be ensured. Moreover, observing the operating instructions helps to: • reduce downtimes and repair costs • prolong the service life of the hydraulic system. Hydraulic oil based on mineral oil is water-endangering and inflammable. It may only be used when the corresponding safety data sheet is available and all precautions prescribed therein were taken. The hydraulic system may only be operated when in technically perfect condition. The use for the intended purpose, performance data and operating conditions must not be changed. Protective equipment / components must not be rendered inoperable, e.g. by bridging limit switches, valves or other control components. If protective equipment must be bridged to allow servicing work to be carried out, precautions must be taken to ensure that no dangerous situation can arise. The higher-order machine operating instructions must be observed.

Safety notes


Adjustment features on components may exclusively be operated or changes to programmable control systems made by authorized personnel within the framework of the intended use of the hydraulic system. In the case of an emergency, fault or other irregularities: • hydraulic systems must be switched off and the main circuit breaker be secured against restarting, • the danger zone must be fenced off in order that nobody can enter the danger zone unknowingly or in an uncontrolled manner, • immediately inform the responsible specialist personnel. Uncontrolled access by external persons to the direct operating area of the hydraulic system is prohibited (even in case that the hydraulic system is at rest).

Note: These are the fundamental safety regulations that must be observed for every project task.

Project 01: Hydraulic power unit


Project 01: Hydraulic power unit Project/trainer information Hydraulics as technology can be assigned to drive technology. The task of drive engineering is to provide a drive for a machine or system that ensures optimum performance of the technological function. This is equally valid for the engine of a passenger car as for the drive of the projects described in this project manual such as the drive of: • feed equipment for the vertical transport of workpieces, • rope winches for lifting loads, • lifting gear for the horizontal transport of loads, • conveyor belts for transporting loads, • feed carriages for tool transport, • punching equipment for punching perforated metal sheets, • rotary drives for relocating workpieces, and • pressing equipment for workpiece pressing. The drive power is made available by an electric motor or combustion engine. The output torque of the motor or engine is converted by a convertor into a rotary or linear movement as required by the machine. This task is assumed by a transmission - in this case, the hydraulic component such as a hydraulic cylinder or a hydraulic motor. The power is transmitted by the hydraulic fluid. The basic components of a hydraulic system are: • Fluid flow generator/pump, • fluid flow consumers/hydraulic cylinders and motors, • open and closed-loop control equipment/valves, • accessories. The components of a hydraulic system listed above can be designed as individual components or, to form a compact assembly, combined in a hydraulic power unit (without consumers). The valves such as directional, pressure and flow control valves are in most of the cases installed separately into a machine. A simple hydraulic power unit consists of: • Hydraulic pump with drive motor, • reservoir for storing the fluid, • instruments for monitoring the fluid level, temperature and pressure, • equipment for fluid care such as filters, coolers and heaters, • valves for pressure relief functions and, if required, • hydraulic accumulators as energy accumulators. In the following Project 01 you can impart knowledge of the general structure of a hydraulic power unit. In the project order, the trainee sets up the required components on the basis of the given requirements. In this project task, he or she is to understand the following: • A hydraulic system consists of a fluid flow generator and a fluid flow consumer (actuator), open and closed-loop control devices and accessories. • In a hydraulic power unit, hydraulic components are grouped to form a compact assembly.

01



• The required drive elements and the accessories such as control and monitoring devices as well as maintenance equipment can be mounted on top or to the hydraulic fluid reservoir. • The size of the power unit, e.g. the capacity of the reservoir, depends on the given conditions and customer requirements. In this project task, the trainee is to set up a power unit on the basis of the conditions listed below and draw a sketch of a schematic diagram: • Hydraulic pump in the form of a pilot operated, variable vane pump with a displacement of qV = 20 l/min; • electric motor for a maximum system pressure of p = 80 bar, • reservoir according to the displacement (3 - 5 times qV), • carrier components, • hydraulic filter with visual, mechanical clogging indicator, • filler and breather filter, • level monitor and • drain valve for changing the hydraulic fluid. A hydraulic accumulator is not provided. Notes on the detailed technical information about hydraulic power units: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, chapter 17 • The Hydraulic Trainer Volume 3/Bosch Rexroth AG Planning and design of hydraulic systems • Technical data sheet RE 51098 Modular standard power units • Technical data sheet RE 10515 Variable vane pump, pilot operated

01



01

Project definition In a hydraulic system for driving lifting equipment for heavy loads, a hydraulic power unit with a variable displacement pump powered by an electric motor and associated accessories is to be used. The customer wishes to get information about the structure of a hydraulic power unit with pilot operated vane pump. In the list of the hydraulic power unit components he requests the provision of short information about the selected components, including a schematic diagram of the hydraulic system and a parts list.

Fig. 01.1 Practical example: Hydraulic power unit with hydraulic pump/el. motor and accessories

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for a standard power unit with pilot operated vane pump (technical qualification) • Handling of hydraulic components in line with functional needs



01

Project steps

Notes

• Informing:

Accepting and understanding the order, among others, through discussions with the customer.

• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of power unit construction parts from a technical data sheet (RE 91098 / modular standard power units).

• Deciding:

Hydraulic design and dimensioning of the power unit.

• Executing::

Preparation of a schematic circuit diagram and selection of the required drive elements and accessories with short description.

• Checking:

Are all customer requirements met?

• Evaluating:

Are there further possibilities of meeting the customer requirement or simpler ways of project execution? Have unforeseeable problems occurred?



01

Hydraulic schematic diagram

Item 10.0

Item 9.0

Measuring glass

Item 6.0

Item 2.0

Item 4.0

Item 7.0 Item 8.0

Item 3.0 Item 1.0

Fig. 01.2 Hydraulic schematic diagram: Drive power unit

Item 5.0



01

Component selection with parts list Item

Qty


Type designation

1.0

1

Reservoir with cover

2.0

1

Variable displacement pump, pilot operated

3.0

1

Level control

FSK

4.0

1

Electric motor

4 KW/1450 rev/ min.

5.0

1

Shut-off valve, operated by turning

6.0

1

Check valve with spring, flow enabled in only one direction; closed at rest position

S6-1X/...

7.0

1

Filter with by-pass valve and pressure measuring device

RF 060...

8.0

1

Tank breather filter

9.0

1

Connection block with 1/4" coupler plug

10.0

1

Measuring glass

Symbol

100 L/steel

PV7-1X/16-30...

Table 01.1 Parts list for hydraulic circuit diagram Fig. 01.2

Notes for the trainer: Items 9.0 and 10.0 listed in the parts list are accessory components for a training system and are not part of a hydraulic power unit in real industrial applications.



01

Safety notes To ensure the operability of plant and machinery, and consequently to allow the recognition of potential risks, safety regulations must be observed before and during the execution of the order. Relevant sources of regulations are given in the introduction of the present manual.

Warning

Caution

If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life. Before starting work on the training stand, make sure that electrical ON/OFF switches on the hydraulic power unit are pressed in, that is, that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy at rest. This can cause injury when the system is opened.

Notes



01

Execution of the order Dimensioning of a hydraulic power unit requires fundamental knowledge of hydraulic control technology. This also includes knowledge of the design of hydraulic systems inclusive of the drive power unit. The listing on the next page shows influencing factors that have to be taken into account when rating a hydraulic power unit. In the project order, only simple rules for the rating of power units can be applied. For this, formulas from physical basic principles can be applied (see Fig. 01.3). Any power losses are not considered.

Piston area AP

Flow control valve Change in velocity

Force F

Force = pressure • area

v Pressure differential ∆p

Energy converter e.g. cylinder

Annulus area AA

Directional valve Start, direction, stop

Force pA 10

F =

F = force in N p = pressure in bar A = area in mm2

Velocity v=

s t

m

v = velocity in s s = travel in m t = time in s

Displacement/flow Vg  n  ηvol qV =

1000

qV = flow in

l min

cm3 rev n = Speed of the pump shaft in rev min

Vg = geometric displacement in

η = volumetric efficiency in %

Pressure control valve Force / pressure limitation

Motor power PM =

PM p qV ηtotal,P

Energy converter e.g. fixed displacement pump

Fig. 01.3 Physical basic principles with formulas

p  qV 600  ηtotal ,P

= = = =

power in kW pressure in bar l flow in min overall efficiency in %



Factors that have an influence on the rating of a power unit • Environment, surroundings - climate • Pipe length to the consumer • Place of installation: integrated - separate • Duty cycle • Expected drive power • Volume fluctuation •

Ambient temperatures – Heat dissipated by the reservoir – Cooling (air, water) – Heating

• Noise - transmitted by pipes and air ducts •

Acoustic insulation – Hoses – Compensators – Anti-vibration mounts – Low flow velocity – Pump selection – Encapsulation – Hydraulic accumulator – Silencers etc.

• Assembly - disassembly - maintenance

Factors that have an influence on the rating of a return flow filter • Field of application, environment • Susceptibility of components (the component with the most stringent requirement determines the filter rating for the entire system!) • The required cleanliness class and filter rating must be adhered to. Both must be specified by the component manufacturer. State of art with regard to minimum requirements is, for example, NAS class 9 and a minimum retention rate of ß10 ≥ 100; ISO 4406 (c) class 20/18/15. • A reliable calculation of cleanliness is impossible, because the ingress of dirt in relation to the ß value cannot be determined. • Arrangement of filters • Type, viscosity and operating temperature of the fluid • Operating pressure • The flow rate determines the selection of the filter size • Permissible Dp across the clean element (Bosch Rexroth selection series: Rated Dp for a pressure filter - 1 bar, return line filter = 0.4 bar) • By-pass valve - determined by the filter series, not provided for pressure filters • Clogging indicator - a MUST in modern hydraulic systems - visual and/or electrical • The tank breather filter must have the same filter rating as the fluid filters.

01


10


Hydraulic pump: The following must be known for rating the hydraulic pump: qV = ? l/min., i.e. which volume is the pump to provide within which time. Since manufacturers usually indicate only the sizes in technical data sheets (how much is displaced during one revolution of the pump?), the speed of the drive/electric motor must be known. In industrial applications, motors of approx. 1,500 rev/min. are employed. For converting the displacement into power per unit of displacement the following formula can be applied: qV =

Vg  n

in l/min 1.000 Because no manufacturer will be able to offer a hydraulic pump with exactly the requested power, the next larger size is usually selected. Electric motor: For rating the electric motor, the possible maximum system pressure must be known apart from the displacement of the hydraulic pump in l/min. Calculation formula for the selection of the hydraulic motor: P=

p • qV 600

in kW

p in bar qV in l/min Also here, the next larger frame size of the manufacturer's electric motor is selected. Typical frame sizes are, e.g. 3 kW, 4 kW, 5.5 kW, 7.5 kW, etc. The selection of the required carrier components such as coupling, pump mounting bracket and damping elements will not be considered here and are not part of the order execution. Hydraulic fluid reservoir: Hydraulic fluid reservoirs are selected on the basis of practical experience such as: Reservoir size = displacement of the hydraulic pump • 5 Whenever possible, standard reservoirs of standardized sizes should be used. The topic of cooling is not dealt with in this simple engineering task. The provision of a drain valve is always recommended for changing the hydraulic fluid. Accessories: In this project task, required accessories for a hydraulic fluid reservoir are a return flow filter, a filler/breather filter and a level control device. For the selection, please refer to technical data sheets of the manufacturers. When selecting the return flow filter, the actual flow required for operating a single-rod cylinder must in any case be taken into account, i.e. how much oil returns from the hydraulic cylinder to the filter (see Project 04). The factors that have an influence on the selection of a return flow filter are listed on the previous page.

01


11


As additional aid for rating a hydraulic power unit we recommend the use of a hydraulic slide rule. For the simplified rating of a return flow filter, see technical data sheet RE 50081. Detailed notes on the engineering and design of hydraulic systems can be found in The Hydraulic Trainer Volume 3/Bosch Rexroth AG. General note: In contrast to the following project tasks, this order execution does not involve any practical work on the training system. A component arrangement drawing and a general layout of the training system are therefore not provided.

Evaluating the work results in relation to the customer requirement • A hydraulic system consists of a fluid flow generator and a fluid flow consumer, valves and accessories. • A hydraulic power unit accommodates the hydraulic components to form a compact unit. • The required drive elements and reservoir accessories such as control and monitoring and maintenance devices can be mounted to or on top of the reservoir. • The size and design of the hydraulic power unit depends on the given conditions and the requirements of the customer.

01


Notes

12


01


Project schedule: Project 01

13


Q. Public, John ………………………………………………………………………………………

Last name, first name


……………………………………………………………………………………………………………

Project handler

Customer requirement:

……………………………………………………………………………………………………………

– Hydraulic circuit diagram

……………………………………………………………………………………………………………

– Parts list

……………………………………………………………………………………………………………

– Information about components

Project designation

Informing from the project definition.

Planning steps

Planning of the project objective and the proceeding.

……………………………………………………………………………………………………………

– System rating/calculation

……………………………………………………………………………………………………………

Understand the circuit diagram

……………………………………………………………………………………………………………

Identifiy components

……………………………………………………………………………………………………………

Supplement parts lists

……………………………………………………………………………………………………………

Rate components

……………………………………………………………………………………………………………

Evaluate the result

…………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Sources of information DIN ISO 1219

……………………………………………………………………………………………………………

The Hydraulic Trainer Volume 1

……………………………………………………………………………………………………………

Project manager

……………………………………………………………………………………………………………

Data sheets

……………………………………………………………………………………………………………

Internet

……………………………………………………………………………………………………………

Hydraulics supplier

……………………………………………………………………………………………………………

Select components from data sheets

……………………………………………………………………………………………………………

Make calculations

…………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Decision-making

Deciding on and selecting components; complementing the circuit diagram and parts list.

……………………………………………………………………………………………………………

(Overleaf)

01


14


01 Summarize the information obtained

…………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Execution of the order

……………………………………………………………………………………………………………

Execution Set-up of the electrohydraulic control and acquisition of required data.

……………………………………………………………………………………………………………

Special points? Pump data sheet RE 10515 is very complex

…………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Comparison of summary with customer requirements

…………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Quality check

……………………………………………………………………………………………………………

Checking Are all customer requirements met?

……………………………………………………………………………………………………………

Evaluating Optimize project steps

(If required, add supplementary sheet)

Assign individual project steps to team members → faster results

……………………………………………………………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Project 01

……………………………………………………………………………………………………………………………………………………………

Note of completion by confirmation of the project manager/place, date, signature

Project 02: Hydraulic variable displacement pump


Project 02: Hydraulic pump/characteristic curve of variable displacement pump Project/trainer information In a hydraulic system, fluid flow generators/hydraulic pumps convert the mechanical energy of a drive motor (torque, speed) into hydraulic power (flow, pressure). The hydraulic pump usually aspires the hydraulic fluid from a storage tank (suction side) and displaces it to the pump outlet (pressure side). In terms of construction, hydraulic pumps can be differentiated as follows: Gear, internal gear, screw, vane, radial piston and axial piston pumps. Hydraulic pumps are displacer pumps, the displacement of which can be either fixed or variable. Hydraulic pumps that feature an adjustable displacement are called variable displacement pumps. The displacement/flow is adjusted by means of mechanical or electronic control systems. In the following Project 02 you can impart knowledge of the interrelationship between the hydraulic variable displacement pump, the displacement and pressure build-up through resistances in the hydraulic system. In the project order, the trainee is made familiar with the characteristic curves of a pilot operated variable displacement vane pump and the direct relationship between the displacement and the system pressure. This project task is to help the trainee to understand the following: • With hydraulic variable displacement pumps, the flow is almost reduced to zero when the system pressure has been reached. • Due to the design of a variable displacement pump, internal leakage oil occurs, which is refed to the reservoir through an external leakage oil line. • The leakage oil flow increases as the resistance rises, which opposes the displacement in the pressure line of the pump • The drained leakage oil flow is the power loss of the hydraulic pump. With the help of the control set up on the training system, the trainee can recognize that when the system pressure increases as resistance at the pressure port of the hydraulic pump, the total displacement reduces. The resistance is realized by means of a hand lever valve, with the system pressure being steplessly variable via a pressure relief valve operated in parallel. Notes on the detailed technical information about hydraulic variable displacement pumps: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, chapter 4 • Technical data sheet RE 10515 Variable vane pump, pilot operated

02



Project definition In a hydraulic power unit, the hydraulic energy is to be provided by a variable, pilot operated vane pump. The power that can be generated by the hydraulic pump is to be measured in an experiment set-up. The customer wishes detailed information about the pros and cons of this vane pump, including a flow characteristic curve, from which the relationship between increasing system pressure and losses of the vane pump can be seen.

Fig. 02.1 Practical example: Vane pump/function elements

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for a pilot operated vane pump (technical qualification) • Handling of hydraulic components in line with functional needs

02



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of components from a technical data sheet (RE 10515 vane pump, pilot operated).

• Deciding:

Preparation of a circuit diagram sketch and selection of components.

• Executing::

Working out the set-up of a hydraulic control on the training system, documenting the characteristic curve required by the customer and providing explanations with regard to the characteristic curves and power losses.

• Checking:


• Evaluating:


02



Hydraulic circuit diagram

02

Item 1.1

Item 1.2

Item 0.1 Item 1.0

Power unit limit

Fig. 02.2 Hydraulic circuit diagram: Test set-up

Measuring glass




Qty


Type designation

1.0

1

Direct operated pressure relief valve; the cracking pressure can be adjusted by means of a spring

DD 1.1

1.1

1


DF 1.2

1.2

1

Shut-off valve, operated by turning

DZ 2.1

0.1

1

Pressure gauge with hose and quick-release coupling, without check valve

DZ 1.4

1

Hydraulic hose with minimess connection

DZ 25.1

Hose with quick-release coupling, with check valve 1

Symbol

VSK 1

Stopwatch


Notes for the trainer: The pilot operated, variable vane pump is not included as individual component in parts list table 02.1. It is an integral part of the hydraulic power unit from Project 01.

02



Component arrangement

Connection block

Measuring glass

02

D

Note: In the case of connection elements marked with “D”, the components can be connected directly with each other.

Fig. 02.3 Recommended component arrangement with component designation for parts list table 02.1 and hydraulic circuit diagram Fig. 02.2

Note: The designations of components in the parts list and the component arrangement are Rexrothspecific designations. Also the grid layout is Rexroth-specific and adapated for use on the training system.

Notes




Warning

Caution

If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise operation of the system, including danger to life. Before starting work on the training stand, make sure that electrical ON/OFF switches on the hydraulic power unit are pressed in, that is, that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy at rest. This can cause injury when the system is opened.

Execution of the order Set-up of the control as described in the following: 1. Mount the components required according to Table 02.1 on the training system in a clearly arranged manner according the prepared circuit diagram.

Connect the hydraulic control according to hydraulic circuit diagram Fig. 02.2 by means of hoses.

For connections, to which pressure gauges with minimess hose DZ 1.4 are to be connected, use hydraulic hoses DZ25. Hand-tighten the pressure gauge measuring lines hand tight at the relevant minimess connection of the hydraulic hose.

The proper and tight fit of hose connections of components can be easily checked by slightly turning the hoses.

Warning

Caution

Make sure that pipes or hoses are connected to all connections - in this case also to minimess lines, or that the connections are plugged by means of plug screws or protective caps. Leakage oil may drip through open connections and cause a slipping risk. Before commissioning the hydraulic control, i.e. before switching the hydraulic pump on, check, whether all pressure control valves are set to minimum pressure (spring unloaded) and all throttle valves are open.

An electrical control is not required for this experiment set-up.

Completely close throttle valve item 1.1. To this end, turn the adjustment element clockwise to the mechanical limit stop. Close shut-off valve item 1.2.

2. Switch the hydraulic pump on and check and the set up control for any leakage. 3. Adjust the system pressure on pressure relief valve item 1.0 to 50 bar plus one turn. 4. Check the set pressure on the variable displacement pump of the drive power unit (zero stroke pressure 50 bar).

02



Flow measurement 5. Open shut-off valve item 1.2. 6. Open throttle valve item 1.1 until a pressure of 15 bar is present at measuring point M1. 7. Flow measurement by means of the measuring glass; to this end, close shut-off valve item 1.2, close the measuring glass, open shut-off valve item 1.2 for 10 s. Record the filling quantity and enter the measured value in Table 02.2. 8. Take flow measurements as described in points 6. to 7. at pressure values of 30 bar, 40 bar, 45 bar and 50 bar and enter the recorded measured values in Table 02.2.

Caution

After completion of practical work, switch the hydraulic pump on the training system off! Turn pressure relief valve item 1.0 back to minimum pressure. Open throttle valve item 1.1 completely. No pressure gauge may indicate a pressure!

9. Calculate the measured oil flow/time and enter it as flow in qV = l/min in Table 02.2. Enter the individual values as points in Diagram 02.3 and connect the individual points with a line to create a curve.

The resulting curve is the typical characteristic curve of the pilot operated, variable vane pump.

Measured values Pressure

p

bar

15

30

40

45

50

Time

t

s

10

10

10

10

10

Volume

V

l

1.32

1.25

1.20

1.10

0

Flow

qV

l/min

7.92

7.50

7.20

6.60

0

Table 02.2 Evaluation of the measured oil volumes

The values were measured at an oil temperature of approx. 20 °C. The values measured by trainees can deviate by 10 %.

02



Flow qV in l/min

02

Operating pressure p in bar Diagram 02.1 Characteristic curve of the hydraulic pump

Evaluating the work result with regard to the customer requirement • On hydraulic variable displacement pumps, the displacement is reduced to almost 0 l/min when the maximum pressure set on the hydraulic pump is reached. • Internal leakage oil in the variable displacement pump must be fed back to the reservoir via an external leakage line. • The amount of leakage oil in the variable displacement pump increases as the resistance/ pressure at the pressure port of the hydraulic pump rises. • The amount of leakage oil corresponds to the power loss of the pump.


10


Notes

02

Project 03: Single-rod cylinder / pressure intensification


Project 03: Single-rod cylinder/pressure intensification Project/trainer information If in a hydraulic system the hydraulic force, which is converted into mechanical energy, is to be transmitted to an actuator in the form of a linear (straight) movement, a hydraulic cylinder is used. We distinguish hydraulic cylinders by their design principles: Plunger, single-rod and double-rod cylinders. The hydraulic cylinder as output element forms the link between the hydraulic circuit and the working element/tool in a technological system. Lifting, lowering, locking and transporting loads are typical applications of hydraulic cylinders. Neglecting friction, the possible maximum cylinder force F in kN depends on the possible maximum system pressure p and the effective piston area A of the hydraulic cylinder, i.e. F = p • A in dN

p in bar; A in cm m2

The piston velocity v in m/s of the hydraulic cylinder is determined by the pump flow supplied. Flow control valves are used to change, i.e. reduce, the piston velocity. When throttling, for example, the piston extension velocity, important physical laws must be taken into account. In the following Project 03 knowledge can be imparted with regard to the use of single-rod cylinders as machine elements. In the project order, the trainee is to work out the physical basic principles of pressure intensification with single-rod cylinders. On the basis of this project task, he/she is to understand the following: • The hydraulic cylinder performs a straight movement and transmits the supplied piston pressure in the form of force. • Double-acting hydraulic cylinders with different piston areas are pressure intensifiers. • Due to adhesive friction in the hydraulic cylinder the pressure actually transmitted via the piston area or through the differences in areas is reduced. • Forces and velocities can be kept constant over the entire stroke. Biased on the control set up on the training system the trainee is to learn that the use of a meterout throttle on the piston rod side involves a risk of pressure intensification. When the hydraulic pump is switched on, the piston of the single-rod cylinder extends. The extension velocity can be varied by means of a throttle valve. Retracting of the single-rod cylinder is accomplished with the help of a 4/2 directional valve. Notes on detailed technical information about hydraulic cylinders: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 7 • Technical data sheet RE 17039 Hydraulic cylinders of tie rod design

03



Project definition A workpiece is to be shifted by a horizontally installed single-rod cylinder to the working range of a simple fixture when the hydraulic pump is switched on. To this end, the extension velocity of the cylinder must be adjustable. Retracting is to be achieved by means of a 4/2 directional valve. The customer installed a throttle valve on the piston rod side and, while adjusting the extension velocity, recognizes that the pressure upstream of the throttle becomes higher than the set system pressure. Apart from the technical documentation he wishes to get an explanation of the pressure intensification of the single-rod cylinder.

Fig. 03.1 Practical example: Hydraulic cylinder of tie rod design

Project tasks • Independent understanding and execution of the task set through application of hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a hydraulic cylinder (specialist qualification) • Handling of hydraulic components in line with functional needs

03



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 17039 Hydraulic cylinders, tie rod design).

• Deciding:

Preparation of a schematic diagram sketch and selection of components.

• Executing:

Set-up of the hydraulic control on the training system. Working out and documenting the system parameters required by the customer and explanations with regard to pressure intensification on the basis of a calculation example.

• Checking:


• Evaluating:


03




03

Item 1.0

Item 0.2

Item 0.3

Item 1.3

Item 1.1

Item 0.1

Item 1.2

Power unit limit

Fig. 03.2 Hydraulic circuit diagram: Feeding cylinder

Measuring glass



Electrical circuit diagram

03

Control 4/2 directional valve Retraction -Single-rod cylinderNote: The single-rod cylinder extends automatically when the hydraulic pump is switched on.

Fig. 03.3 Wiring diagram re hydraulic circuit diagram Fig. 03.2




Qty

1.0

1


ZY 1.3

1.1

1


DW 3 E

1.2

1


DD 1.1

1.3

1


DF 1.2

1


DZ 4.1

3


DZ 1.4

3


DZ 25.1

0.1 - 0.3


Hose Table 03.1 Parts list for hydraulic circuit diagram Fig. 03.2

Type designation

VSK 1

Symbol

03




Connection block

Measuring glass

03

D


Fig. 03.4 Recommended component arrangement with component designations for parts list Table 03.1 and hydraulic circuit diagram Fig. 03.2

Note: The designations of components in the parts list and the component arrangement are Rexrothspecific designations. Also the grid arrangement is Rexroth-specific and adapted for use on the training system.

Notes




Warning

Caution

If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life. Before starting work on the training stand, check that the electrical ON/ OFF switch on the hydraulic power unit is pressed in, i.e. that the system is switched off. Use the system pressure gauges to check that the system is depressurized. Hydraulic systems can store pressure energy when at rest. It can cause injury when the system is opened.

Execution of the order Set up the control as described below: 1. Mount the components required according to Table 03.1 in a clearly arranged form on the training system according to the prepared circuit diagram.


For connections, to which pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25. Hand-tighten the pressure gauge measuring lines at the relevant minimess connection of the hydraulic hose.

The correct and proper fit of the component connections with hoses can be checked by slightly turning the hoses.

Warning

Caution


Wire the electrical control according to wiring diagram Fig. 03.3.

2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Check the pressure set on the variable displacement pump of the drive power unit (if required, correct to 50 bar). 4. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn; operate push-button S2 to prevent the piston of hydraulic cylinder Item 1.0 from extending. 5. Through operation of push-button S1 the control voltage of solenoid Y1 of the 4/2 directional valves Item 1.1 drops, and the piston of the hydraulic cylinder extends due to the pump flow supplied directly to the piston side.

03



6. Switch the hydraulic pump off and wait until the system is depressurized. Close throttle valve Item 1.3. To this end, turn in the adjustment element counter-clockwise to the limit stop. 7. Switch the hydraulic pump on. The piston of the hydraulic cylinder cannot extend, because the counterforce on the piston rod side is greater than the force on the piston side, since the throttle valve is closed. Pressure gauge M3 indicates the value of pressure intensification. Note the measured values and enter them in Table 03.2.

Caution

After having completed practical work on the training system switch the hydraulic pump off! Turn pressure relief valve Item 1.2 back to minimum pressure. No pressure gauge may indicate a pressure!

Measured values Hydraulic cylinder

Measuring point M1 System pressure p in bar

M2 piston side p in bar

M3 piston rod side p in bar

48

48

82

Extending/ Y1 not operated

Table 03.2 Pressure intensification values measured

The values were measured at an oil temperature of approx. 20 °C. The values measured by the trainees can deviate by 10 %.

Additional task in conjunction with the customer requirement: Calculation of the pressure intensification on the basis of given hydraulic cylinder values. Hydraulic cylinder of tie rod design: Type CD T3...25/18...200 Bore: Piston rod diameter:

25 mm 18 mm

Apiston = 4,91 cm2 Arod = 2,54 cm2 Aannulus = 2,3 37 cm2

4,91 cm2 2,54 cm2

= 2,07 : 1

If the meter-out throttle is completely closed, then: FK = FR pK  AK = pR  AR 2,07 pR =  50 bar = 103,5 bar 1,00

03


10


Evaluating the work results with regard to the customer requirement • Hydraulic cylinders perform linear movements and transmit the piston pressure in the form of force. • Double-acting hydraulic cylinders with different areas are called single-rod cylinders. • Single-rod cylinders are pressure intensifiers. • Velocities can be kept constant over the entire stroke.

03

Project 04: Single-rod cylinder/flow


Project 04: Single-rod cylinder/flow Project/trainer information If a hydraulic cylinder in a hydraulic system is not only to transmit the force, but also work in the form of piston velocity, double-acting hydraulic cylinders are used such as: single-rod and double-rod cylinders. Due to the different areas, single-rod cylinders feature different piston velocities, even if the pump flow provided remains unchanged. Here, the load force generated by the moved workpiece often has an influence on the piston velocity (see Project 09 - 10). Due to the area ratio of the piston side to the piston rod side, different flows occur during extending and retracting of the cylinder. To prevent high flow velocities in the connected hoses and pipes, the latter must be selected taking into account the given flow supplied by the hydraulic pump and the area ratio of the single-rod cylinder.

AK

AK

AR

AR

=ϕ

Area ratio of the single-rod cylinder 40 20

10 Values in l/min

20

e.g.

qV = 20 l/min ϕ = 2 : 1

The following Project 04 is intended to impart knowledge of the use of single-rod cylinders as machine element, in particular with reference to the piston velocities and flows. In this project order, the trainees are to be made familiar the velocity behavior during the extension and retraction of the cylinder piston of single-rod cylinders. Through this project task, they are to understand the following: • The piston velocity of a double-acting cylinder - single-rod cylinder - depends on the cylinder size and the supplied flow. • The different piston areas result in different flow velocities, which have an influence on the selection of connection elements, the line system and power unit accessories such as filtration and cooling systems. • In the case of double-rod cylinders, the forces transmitted and the piston velocities are identical in both directions of action of the piston. On the basis of the control set up on the training system the trainees are to recognize that the cylinder piston retracts and extends at different velocities. When the hydraulic pump is switched on, the piston of the single-rod cylinder extends. Controlled by a 4/2 directional valve, the piston of the hydraulic cylinder retracts. The extension and retraction velocity can be changed by means of a throttle valve on the piston rod side. Notes on detailed technical information about hydraulic cylinders: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 7 • Technical data sheet RE 17039 Hydraulic cylinders, tie rod design

04



Project definition Like in Project 03 a workpiece is to be moved to the working range of a simple fixture by a horizontally installed single-rod cylinder when the hydraulic pump is switched on. To this end, the extension velocity of the cylinder must be adjustable. The return is to be accomplished with the help of a 4/2 directional valve. The customer observes that with an open throttle valve the piston velocities during extending and retracting of the cylinder are different. Apart from the technical documentation, he wishes to obtain an explanation with regard to the different piston velocities of the single-rod cylinder. He also requests details about the filling volume of the hydraulic cylinder used.

Fig. 04.1 Practical example: Schematic illustration of flow velocities in the single-rod cylinder

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a hydraulic cylinder (specialist qualification) • Handling of hydraulic components in line with functional needs

04



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 17039 Hydraulic cylinders of tie rod design).

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Prepration and documentation of the information and explanations with regard to the single-rod cylinder as demanded by the customer.

• Checking:


• Evaluating:


04




Item 1.0

04 Item 0.2

Item 0.3

Item 1.1

Item 0.1

Item 1.3

Item 1.2

Power unit limit

Fig. 04.2 Hydraulic circuit diagram: Feed cylinder

Measuring glass




04

Control 4/2 directional valve Retraction -Single-rod cylinderNote: The single-rod cylinder extends automatically when the hydraulic pump is switched on.

Fig. 04.3 Wiring diagram re hydraulic circuit diagram Fig. 04.2




Qty


Type designation

1.0

1

Double-acting cylinder with singlesided piston rod

ZY 1.3

1.1

1


DW 3 E

1.2

1


DD 1.1

1.3

1


DF 1.2

1


DZ 4.1

3


DZ 1.4

3


DZ 25.1

0.1 - 0.3

Hose 1

Stopwatch

1

Flowmeter


VSK 1

DZ 30

Symbol

04




��

��

��

��

04

��

Measuring glass

��

��

�

��

��

Note: The component arrangement shows the optional variant with electronic flow measurement

��

D

�

�

�

�

��

�

��

�

Connection block

��

��

�


��

��



Notes




Warning

Caution

If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life. Before starting work on the training system, check that the electrical ON/ OFF switch on the hydraulic power unit is pressed in, i.e. that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy when at rest. It can cause injury when the system is opened.





Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Check the pressure set on the variable displacement pump of the drive power unit (if required, correct to 52 bar). 4. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn; operate push-button S2 to prevent the piston of hydraulic cylinder Item 1.0 from extending. 5. Due to the operation of push-button S2 the control voltage of solenoid Y1 of the 4/2 directional valve Item 1.1 drops and the piston of the hydraulic cylinders extends due to the pump flow fed directly to the piston side. 6. The extension velocity of hydraulic cylinder piston Item 1.0 is to be adjusted to 5 s by means of throttle valve Item 1.3 while directional valve Item 1.1 is not operated.

04



7. Measure the pressures at measuring points M1, M2, M3 during extending, retracting and at the relevant end position of the cylinder and enter the values in Table 04.2.

Establish the time required for extending and retracting by means of a stopwatch and enter the values also in Table 04.2.

Caution

After having completed practical work on the training system switch the hydraulic pump off! Turn all pressure valves of the electrohydraulic control back to minimum pressure. Completely open throttle valves, if installed. No pressure gauge may indicate a pressure!

Measured values Hydraulic cylinder Piston position

Position 4/2 directional valve

M1 M2 M3 p in bar p in bar p in bar

t in s

v in m/s

V in l

Extending

b

49

0

0

5

0.051

-

Extended

b

50

49

0

-

-

0.098

Retracting

a

49

0

6

3.2

0.073

-

Retracted

a

50

0

49

-

-

0.058

Table 04.2 Values of velocity/flow measurement


Additional task in conjunction with the customer requirement: Calculation of the filling volume of the single-rod cylinder used for the execution of the order (enter calculated values in Table 04.2). Hydraulic cylinder of tie rod design Bore: 25 mm Piston rod diameter: 16 mm Piston stroke:

Apiston = 4.91 cm2 Arod = 2.01 cm2 Aannulus = 2.90 cm2

200 mm = 20 cm

V = A • s Fill: Piston volume:

Type: CD T3...25/16...200

A in cm2 s in mm V in l

V = 4.91 cm2 • 20 cm = 98.2 cm3 = 0.098 l V = 2.90 cm2 • 20 cm = 58.0 cm3 = 0.058 l

04


10


Evaluating the work results with regard to the customer requirement • The extension and retraction velocity of a single-rod cylinder piston depends on the supplied hydraulic pump flow and the cylinder areas. • With double-rod cylinders with identical piston rods on both sides, the piston velocities are identical in both directions.

04

Project 05: Hydraulic motor


Project 05: Hydraulic motor Project/trainer information If the hydraulic force is to be transmitted via a rotary movement to an actuator in a hydraulic system, a hydraulic motor is used. Hydraulic motors are distinguished by their design principle: Gear, gear wheel/planetary gear, vane, radial piston and axial piston motors. In functional terms, a hydraulic motor is the inversion of a hydraulic pump. Hydraulic pumps convert the mechanical energy, which is fed to the pump via a drive shaft, into hydraulic energy. Hydraulic motors convert hydraulic energy into mechanical energy. In principle, a hydraulic motor is a hydraulic pump, which works in the opposite direction and with which both directions of rotation are possible. If you connect a hydraulic pump directly to a hydraulic motor in a closed circuit you get a hydrostatic gearbox, which is steplessly adjustable by means of appropriate control systems. The following Project 05: Hydraulic motor is intended to gain knowledge of the operating principle and the use of hydraulic motors. In the project order, the trainee is to get familiar with the operating features of a hydraulic motor. Through this project task, he/she is to understand the following: • Hydraulic motors convert hydraulic energy into torque and speed. • The direction of rotation or the direction of flow of hydraulic motors can be controlled by means of a directional valve. • The speed of the hydraulic motors is determined by the flow provided and by the swept volume of the hydraulic motors. • The torque of hydraulic motors is determined by the differential pressure between the inlet and the outlet and by the swept volume. By the control to be set up on the training system, the trainee can recognize the operating principle of a hydraulic motor. 4/3 directional valves can be used to implement clockwise and counter-clockwise running of the hydraulic motor. The speed of the hydraulic motor can be changed by means of a meter-in throttle. For a positioned standstill of the hydraulic motor the return line (T) of the 4/3 directional valve is pre-loaded by means of a pressure relief valve.

Notes on detailed technical information about hydraulic motors: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 5 • Technical data sheet RE 91001 Fixed displacement axial piston motor

05



Project definition Heavy loads are to be lifted and lowered by means of a rope winch. The velocity of the rope winch is to be adjustable. For space reasons, the use of a hydraulic cylinder is impossible, i.e. the rope winch must be powered by a hydraulic motor. Also an electrical solution is not desirable due to changing loads. In order that the customer can understand the hydraulic solution proposed, he requires technical documentation such as a hydraulic circuit diagram with parts list and the required measured data such as an evaluation of the differential pressure across the hydraulic motor at different flows.

Fig. 05.1 Practical example: Winch for lifting heavy loads

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a hydraulic motor (specialist qualification) • Handling of hydraulic components in line with functional needs

05



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 91001 Axial piston motor).

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out and documenting the system parameters required by the customer.

• Checking:


• Evaluating:


05




Item 0.2

Item 0.3

Item 1.0

05 Item 1.1 Item 0.4 Item 1.4

Item 1.3

Item 0.1

Item 1.2

Power unit limit

Fig. 05.2 Hydraulic circuit diagram: Lifting platform control

Measuring glass




05 Stop

Control 4/3 directional valve

Fig. 05.3 Wiring diagram for hydraulic circuit diagram Fig. 05.2

Rotation Rotation -Hydraulic motor-




Qty

1.0

1


1.1

1


DW 13 E

1.2/1.4

2


DD 1.1

1.3

1


DF 1.2

1


DZ 4.1

4


DZ 1.4

4


DZ 25.1

0.1 - 0.4


Hose 1

Stopwatch

1

Tachometer

1

Flowmeter


Type designation

Symbol

DM 8

05

VSK 1

DZ 30




Connection block

Measuring glass

05

D




Notes



Component arrangement/optional


Connection block

Measuring glass

05

D




Notes




Warning

Caution






Warning

Caution

Make sure that all ports - in this case also minimess lines - pipes and hoses are connected or that the ports are blocked with plug screws or protective caps. Leakage oil can drop through open ports on the floor and cause a risk of slipping. Before commissioning the hydraulic control, i.e. before switching the hydraulic pump on, check, whether all pressure control valves are set to minimum pressure (spring unloaded) and all throttle valves are open.


2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Check the set pressure on the variable displacement pump of the drive power unit (if required, correct to 50 bar). 4. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn.

Completely open throttle valve Item 1.3.

05


10


In the next working step the hydraulic motor rotates. Take care that clothes, hair, etc. cannot get caught by the motor plate. Caution

5. By actuating push-button S4 solenoid Y1b of 4/3 directional valve Item 1.1 is energized. Hydraulic motor Item 1.0 rotates clockwise.

While the hydraulic motor is rotating, adjust preload pressure M4 to 20 bar by means of pressure relief valve Item 1.4.

6. Close throttle valve Item 1.3, then open it by � turn (the first value given in Table 05.2). 7. By actuating push-button S2 solenoid Y1a of 4/3 directional valves Item 1.1 is energized. The hydraulic motor rotates counter-clockwise.

Use the measuring glass and a stopwatch or optionally an electronic flow measuring system to acquire the flow qV in l/min and enter the values in Table 05.2. Also measure pressures M1, M2, M3, M4 and enter them in Table 05.2.

8. Continue to set throttle valve Item 1.3 to the values given in Table 05.2 and enter the measurement result in Table 05.2.

Measure all specified values for the clockwise direction of rotation.

Caution

After having completed practical work on the training system switch the hydraulic pump off! Turn pressure relief valve Item 1.2 back to minimum pressure, completely open throttle valve Item 1.3. No pressure gauge may indicate a pressure!

Measured values Adjustment of speed of rotation Throttle valve Item 1.3

M1 M2 M3 M2 - M3 M4 qV n p in bar p in bar p in bar Dp in bar p in bar in l/min in min-1

Throttle closed

50

0

0

0

0

0

0

� turn opened

49

20

17.5

2.5

15

2

264 *

½ turn opened

48

22

19

3

16

2.6

335 *

1 turn opened

48

25

21

4

17.5

3.7

435 *

1 ½ turn opened

48

30

25

5

18

4.7

540 *

2 turns opened

48

31

25

6

19

5.1

595 *

More than 2 ½ turns opened

48

34

27

7

19

5.7

655 *

Table 05.2 Measured values from the work order for counter-clockwise direction of rotation of the motor * The values in column 8 were established by means of a speed sensor.


05


11


Additional tasks: Calculation of the output power at maximum speed using the formulas below. P=

qV =

n=

∆ p • qV 600

in kW

V • 60 t qV • ηvol Vg

• 1000

P = output power in kW p = pressure in bar qV = swept volume in l/min V = content of the measuring glass in l t = measuring time in s n = drive speed in min-1 hvol = volumetric efficiency of the motor Vg = geometric swept volume (displacement) of the motor in cm3/rev hvol = 0.8 Vg = 4.93 cm3/rev - DM2

Evaluating the work results with regard to the customer requirement • Hydraulic motors convert hydraulic energiy into torque and speed. • The direction of rotation of hydraulic motors can be controlled by means of a directional valve. • The speed of hydraulic motors is determined by the supplied hydraulic pump flow and by the swept volume of the hydraulic motors. • The torque of hydraulic motors is determined by the differential pressure and the swept volume.

05


12


Notes

05

Project 06: 4/3 directional valve


Project 06: 4/3 directional valve Project/trainer information If the travel, direction, start, and stop of a hydraulic cylinder is to be controlled in a hydraulic system, a directional valve must be used. Directional valves are differentiated as follows: Directional spool valves, direct operated, pilot operated and directional poppet valves. Directional valves are elements that assume the task of opening, closing or changing the flow paths in hydraulic systems. The spool of a directional valve is installed with a certain clearance. This clearance causes a continuous leakage oil flow. This leakage, which is not externally visible, results in a flow loss that increases as the pressure rises. When a directional valve is used for controlling a hydraulic cylinder, pressure/force losses occur on the hydraulic cylinder when the fluid flows through the valve. Possible applications and the operating characteristics of the directional valve are determined by, among others, the selection of the valve spool. The valve spool also determines the form of the symbol. The following Project 06: 4/3 directional valve is intended to gain knowledge of the operating principle and the possible applications of direct operated directional valves. In the project order the trainee is to work out and document the following: • The spool shape determines the symbol, and all directional spool valves feature internal leakage for design reasons caused by the clearance of the spool in the valve housing. • With a valve being in the blocked position: – a connected single-rod cylinder can extend due to internal leakage of the valve while the valve is in its rest position and the pump is running. – the total flow of a fixed displacement pump flows via the pressure relief valve to the tank when the set system pressure is reached while the pump is running and the valve is in its rest position, i.e. high power losses incur and the oil heats up. – the working pressure utilized last slowly decreases via the clearance of the spool when the hydraulic pump is switched off and the valve is in its rest position. • With a valve being in the circulation position: – when the valve is in its rest position and the pump is switched on the total pump flow flows almost at zero pressure to the tank; the backpressure and hence the power loss is determined by the pressure differential across the valve; – energy is saved while the pump is running and the valve is in its rest position. This feature cannot be installed in controls, where the system pressure is required by further actuators. With the help of the control set up on the training system the trainee gets familiar with the possible application of a 4/3 directional valve. A hydraulic cylinder is to be controlled alternately by a 4/3 directional valve with different spool shapes (blocked and circulation position). The trainee can recognize the special features of different symbols by measuring the different pressure differentials across the 4/3 directional valve. Internal leakage can be recognized by the horizontal arrangement of the single-rod cylinder, on which no external forces act. Notes on detailed technical information about direct operated directional valves: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG • Technical data sheet RE 23178 4/3, 4/2 and 3/2 directional valves with wet pin solenoids

06



Project definition A single-rod cylinder is to shift and position tools horizontally in a fixture. When in the rest position the hydraulic cylinder must not move, and the fixed displacement pump is to be spared and thus energy saved. The customer wants to be informed about the pros and cons of the various spool shapes, in particular blocked and circulation position. In order that the customer can understand your proposed solution, he requires technical documentation such as the hydraulic circuit diagram with parts list, and the required measured data for the spool shapes/symbols.

06

Fig. 06.1 Practical example: Section of a 4/3 directional valve

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a directional valve (specialist qualification) • Handling of hydraulic components in line with functional needs



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 23178/4/3 directional valve).

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out and documenting the system parameters as required by the customer.

• Checking:


• Evaluating:


06



Hydraulic circuit diagram/task 1

Item 1.0

Item 0.2

Item 0.3

06

Item 1.1

Item 0.1 Item 1.3

Power unit limit

Fig. 06.2 Hydraulic circuit diagram: Tool carriage control 1

Measuring glass



Electrical circuit diagram/task 1

06

Circulation



Extension Retraction -Single-rod cylinder-



Hydraulic circuit diagram/task 2

Item 1.0

Item 0.2

Item 0.3

06

Item 1.2

Item 0.1 Item 1.3

Power unit limit

Fig. 06.4 Hydraulic circuit diagram: Tool carriage control 2

Measuring glass



Electrical circuit diagram/task 2

06

Stop



Retraction Extension -Single-rod cylinder-




Qty

1.0

1


ZY 1.3

1


DW 4E

1.2

1


DW 13E

1.3

1


DD 1.1

1


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

1.1

0.1 - 0.3

1


Flowmeter

Table 06.1 Parts list for hydraulic circuit diagrams Fig. 06.2 and 06.04

Type designation

Symbol

06

DZ 30.N




Connection block

Measuring glass

Component arrangement/task 1

06

D




Notes


10



Connection block

Measuring glass

Component arrangement/task 2

06

D




Notes


11



Warning

Caution


Execution of the order Task 1

Set-up of the controls as described below: 1. Mount the components required according to Table 06.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set the system pressure on pressure relief valve Item 1.3 to 30 bar, and: By actuating push-button S4 solenoid Y1b of 4/3 directional valve Item 1.1 is energized. The pump flow is fed against the piston rod side of hydraulic cylinder Item 1.0 and the system pressure can be set to 30 bar. 4. By actuating push-button S2 solenoid Y1a of 4/3 directional valve Item 1.1 is energized. The piston of the hydraulic cylinder extends.

06


12


Measurements for task 1: 5. Measure the specified values in the end positions of the hydraulic cylinder and in the rest position (central position) of the 4/3 directional valve as listed in Table 06.2 and enter the values in Table 06.2.

Caution

Task 2

After having completed practical work on the training system switch the hydraulic pump off! Turn pressure relief valve Item 1.3 back to minimum pressure. No pressure gauge may indicate a pressure!

6. Modify the hydraulic control according to hydraulic circuit diagram 06.4. Proceed as described in task one, steps 1 and 2.

Check the electrical control for correct wiring.

7. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 8. Set the system pressure on pressure relief valve Item 1.3 to 30 bar. 9. By actuating push-button S4 solenoid Y1b of 4/3 directional valve Item 1.2 is energized. The piston of hydraulic cylinder Item 1.1 extends. By actuating push-button S2 the piston of the hydraulic cylinder retracts. In contrast to task 1, positions "a“ and "b“ of the 4/3 directional valve are exchanged due to the spool shape/symbol. Measurements for task 2: 10. Measure the specified values in the end positions of the hydraulic cylinder and in the rest position (central position) of the 4/3 directional valve as listed in Table 06.3 and enter the values in Table 06.3.

Caution

After having completed practical work on the training system switch the hydraulic pump off! Turn pressure relief valve Item 1.3 back to minimum pressure. No pressure gauge may indicate a pressure.

Measured values for task 1 Hydraulic cylinder Position

Directional valve position

M1 p in bar

M2 p in bar

M3 p in bar

qV in l/min

Piston extended

a

30

30

0

7.66

Piston retracted

b

30

0

30

7.66

Rest position of piston

0

8

5

8

0

Table 06.2 4/3 directional valve with circulation position

06


13


Measured values for task 2 Hydraulic cylinder Position

Directional valve position

M1 p in bar

M2 p in bar

M3 p in bar

qV in l/min

Piston extended

b

30

30

0

7.66

Piston retracted

a

30

0

30

7.66

Piston at rest position

0

30

7

9

7.66

Table 06.3 4/3 directional valve with blocked position

06 The values were measured at an oil temperature of approx. 20 °C. The values measured by the trainees can deviate by 10 %.

Evaluating the work results with regard to the customer requirement • With a 4/3 directional valve with circulation position the total flow of the hydraulic pump is fed back to the tank almost at zero pressure when the directional valve is in its rest/central position. The pressure differential, and hence the power loss, is determined by the spool shape of the directional valve and by line resistances in the return line. • With a 4/3 directional valve with circulation position, energy is saved due to the pressureless circulation in der central position, but this valve can not be used, if further actuators are to be controlled by an additional directional valve. • With a 4/3 directional valve with blocked position, the total flow of a fixed displacement hydraulic pump is fed via the pressure relief valve to the tank in the rest/central position of the directional valve when the system pressure is reached. The hydraulic fluid heats up and a high power loss incurs. • With a 4/3 directional valve with blocked position a connected single-rod cylinder can extend due to internal leakage oil while the directional valve is in its rest position and the fixed displacment pump is running. The working pressure utilized last slowly decreases via the clearance between spool/ housing.


14


Notes

06

Project 07: Check valve


Project 07: Check valve Project/trainer information If the flow in hydraulic system is to be blocked in one direction, a check valve is required. Check valves are available as seat valves, with ball or poppet as closing element. They are subdivided as follows: Check valves, pilot operated check valves. Through the installation of a check valve it is possible to prevent, for example, the load pressure from driving a hydraulic pump reversely when the electric motor is switched off. Also pressure peaks, e.g. upstream of filters or coolers, can be reduced by means of a check valve installed in a by-pass. However, the use of a check valve also results in additional resistance in the system so that a greater power must be installed. The following Project 07 can be used to impart knowledge of the operating principle and the use of a check valve. In the course of the project order the trainee is to understand the operating principle of a check valve installed in a by-pass. Through this project tasks he/she is to recognize the following: • Fluid can only flow through a check valve in one direction. • A check valve results in additional hydraulic resistance in the system. • Pressure peaks can be reduced with the help of a check valve installed in a by-pass. • When loads are secured by a check valve on the piston rod side, there is a risk of pressure intensification. On the basis of the control set up on the training system the trainee is to understand the operating principle of a check valve. A hydraulic cylinder under load, which is secured by a check valve, can be lowered by operating a shut-off valve. The cylinder velocity can be adjusted by means of a throttle. To provide protection against pressure intensification a pressure relief valve is to be installed on the piston rod side. Notes on detailed technical information about the check valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 10 • Technical data sheet RE 20375 Check valve

07



Project definition In a fixture, a load suspended on a vertical cylinder is to be held by means of a check valve. Lowering of the load should be possible with a shut-off valve. The piston rod side is to be protected by means of a pressure relief valve. (The lowering movement via the electrical control is not an integral part of the order). The velocity is to be adjustable. In order that the customer can understand your proposed solution, he requires technical documentation. In addition, he wants to know whether particular problems could arise, if a check valve is installed on the piston rod side.

07

Fig. 07.1 Practical example: Check valve

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a check valve (specialist qualification) • Handling of hydraulic components in line with functional needs



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 20375 Check valve).

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out and documenting the system parameters requred by the customer.

• Checking:


• Evaluating:


07



Hydraulic circuit diagram Item 1.0

Item 0.3

Item 1.6 Item 0.2 Item 1.5

Item 1.3

07

Item 1.4

Item 1.1

Item 0.1

Item 1.2

Power unit limit

Fig. 07.2 Hydraulic circuit diagram: Control of a vertical cylinder with suspended load

Measuring glass




07 (Emergency stop) Stop

Control 4/3 directional valve Retraction -Single-rod cylinder* Solenoid Y1.b is not energized

Fig. 07.3 Wiring diagram re hydraulic circuit diagram 07.2




Qty

1.0

1

Double-acting cylinder with single-sided piston rod with load

1.1

1

4/3 directional valve with direct actuation by two solenoids, spring centering of the central position and central position P, A - B - T

DW 10E

1.2/1.5

2


DD 1.1

1.3

1


DS 2.1

1.4

1

Shut-off valve, actuated by turning

DZ 2.1

1.6

1


DF 1.2

3


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

0.1 - 0.3



Type designation

Symbol

ZY 1.Last

07



Measuring glass


Connection block

07 D


Fig. 07.4 Recommended component arrangement with component designation for parts list Table 07.1 and hydraulic circuit diagram Fig. 07.2





Warning

Caution






Warning

Caution


Wire the electrical control according to wiring diagram Fig. 07.3. Observe the installation direction of check valve Item 1.3. Warning

2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn (in pressure line M1).

07



4. By actuating push-button S2 solenoid Y1a of 4/3 directional valve Item 1.1 is energized, i.e. the cylinder retracts. Opening of shut-off valve Item 1.4 causes the cylinder to extend. 5. Safety valve setting against pressure intensification on the piston rod side:

Starting position of the cylinder: B.D.C. (bottom dead center, cylinder extended).

Close shut-off valve Item 1.4. Set pressure relief valve Item 1.5 on the piston rod side to maximum pressure (spring tensioned - 1 turn).

Move the cylinder to the U.D.C. by operating push-button S2. Move directional valve Item 1.1 by manual operation to position Y1b while opening pressure relief valve Item 1.5 on the piston rod side until pressure gauge M3 indicates a pressure of 80 bar (safety setting against pressure intensification on the piston rod side). Check the set value by extending the cylinder again.

6. Check lowering of the load in the de-energized condition by opening shut-off valve Item 1.4.

The lowering velocity can be adjusted by means of throttle valve Item 1.6.

The pressure that builds up when the cylinder supports on the counterforce of pressure relief valve Item 1.5 on the piston rod side is called load holding pressure. To determine the load holding pressure, the cylinder must be at the U.D.C. While the shut-off valve is closed, slowly open the pressure relief valve until the cylinder starts to lower. M3 indicates the load holding pressure. On the basis of the load holding pressure and the dimensions of the hydraulic cylinder the weight of the load can be calculated.

Note: To prevent pressure intensification, a safety valve (pressure relief valve) is used in practical applications, e.g. in a welding fixture. The upward stroke is accomplished via a check valve installed in parallel.

Caution

After having completed practical work on the training system switch the hydraulic pump off! Set the throttle valve and the pressure relief valves to minimum pressure. For the disassembly, the load must be lowered. No pressure gauge may indicate a pressure!

Evaluating the work results with regard to the customer requirement • Fluid can flow through a check valve only in one direction. • Load securing by means of a check valve on the piston rod side involves the risk of pressure intensification. • The installation of a check valve results in the build-up of additional resistance in the direction of flow. • A check valve can be used as safety valve, e.g. to provide protection against pressure peaks.

07


10


Notes

07

Project 08: Check valve, pilot operated


Project 08: Check valve, pilot operated Project/trainer information In contrast to simple check valves, pilot operated check valves can also be opened in the direction opposite to the direction of flow (direction of closure). Pilot operated check valves can be installed for isolating pressurized working circuits (hydraulic isolation of a hydraulic cylinder) or for providing protection against lowering of a load in the event of a line rupture. In the following Project 08 you can impart knowledge of the operating principle and the use of a pilot operated check valve. In the project order, the trainee has to make himself/herself familiar with the operating principle of a pilot operated check valve, when it is opened by an additional hydraulic control signal. With the help of a practice-oriented experiment set-up on the training system he/she is to undertand the following: • Fluid can only flow through a hydraulically pilot operated check valve in the checking direction, if it is opened by means of a hydraulic control signal. • The check valve can only be closed when the pilot line is depressurized. • The check valve can only close properly, if the fluid can freely flow from the closing element to the reservoir. • To prevent decompression shocks when the check valve opens, components are used that feature a pre-opening function of the main poppet. With the help of a control set up on the training system for a lifting apparatus, the trainee can see the operating principle of a pilot operated check vave. A hydraulic cylinder under load (vertical cylinder with suspended load) is secured by a pilot operated check valve. This pilot operated check valve is opened by means of a 4/2 directional valve. The lowering speed can be adjusted with a throttle. A pressure relief valve on the piston rod side provides a pressure relief function for pressure intensifications. Notes on the detailed technical information about the direct operated pressure relief valve: • The Hydraulic Trainer Volume 1, Bosch Rexroth AG Basic principles and components, chapter 10 • Technical data sheet RE 21460 Check valve

08



Project definition A cylinder in a rig (gripper) is to be protected against lowering by a pilot operated check valve. The hydraulic control from Project 07 is to be modified according to the customer requirements. In order that the customer can understand your proposed solution, he requires the modified technical documentation. As the lowering speed should also be adjustable here, the customer wants to know, at which position the throttle valve can be installed. Moreover, he wants to know at which pilot pressure the pilot operated check valve opens.

08

Fig. 08.1 Practical example: Hydraulically pilot operated check valves in a rig (gripper)

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for a pilot operated check valve (technical qualification) • Handling of hydraulic components in line with functional needs



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 21460 / pilot operated check valve).

• Deciding:


• Executing::


• Checking:


• Evaluating:


08




Item 0.3

Item 1.6

Item 0.2

Item 1.4

Item 1.3

Item 1.5

08 Item 1.1

Item 0.1

Item 1.2

Power unit limit

Fig. 08.2 Hydraulic circuit diagram: Check valve, hydraulically pilot operated

Measuring glass




Stop

08

Control 4/3 directional valve - 4/2 directional valve Retraction Extension Unlocking -Single-rod cylinder-

Note: Extension = Y1.b + Y2

Fig. 08.3 Wiring diagram for hydraulic circuit diagram 08.2




Qty

1.0

1

Double-acting cylinder with piston rod with load on one side

ZY 1.Last

1.1

1

4/3 directional valve with direct actuation by two solenoids, spring centring of the central position and central position P, A - B - T

DW 10E

1.2/1.5

2


DD 1.1

1.3

1

4/2 directional valve with solenoid operation, spring return

DW 3E

1.4

1

Pilot operated check valve, with spring, flow possible in both directions due to pilot pressure

DS 1.1

1.6

1


DF 1.2

3

Distributor plate with four connections

DZ 4.1

3


DZ 1.4

3

Hose with quick-release coupling, with check valve

DZ 25

Hose

VSK 1

0.1 - 0.3



Type designation

Symbol

08



Measuring glass


Connection block

08 D







Warning

Caution

If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise operation of the system, including danger to life. Before starting work on the training stand, make sure that electrical ON/OFF switches on the hydraulic power unit are pressed in, that is, that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy at rest. This can cause injury when the system is opened.

08 Execution of the order Set-up of the control as described in the following: 1. Mount the components required according to Table 08.1 on the training system in a clearly arranged manner according the prepared circuit diagram.


For connections, to which pressure gauges with minimess hose DZ 1.4 are to be connected, use hydraulic hoses DZ25. Hand-tighten the pressure gauge measuring lines hand tight at the relevant minimess connection of the hydraulic hose.


Warning

Caution



2. Switch the hydraulic pump on and check the set up control for leakage. No pressure gauge may indicate a pressure. 3. Adjust the system pressure on pressure relief valve item 1.2 to 50 bar plus one turn. 4. The operation of pushbutton S2 causes the energization of solenoid Y1a of 4/3 directional valve item 1.1, i.e. the cylinder retracts. Turn item 1.5 in until the cylinder starts to move.


Caution


Only operate S3; turn in pressure relief valve completely, then turn pressure relief valve out until 80 bar is applied at M3. The cylinder is to come to a standstill.

5. The actuation of pushbutton S3 causes 4/3 directional valve item 1.1 to be operated, i.e. pressure is supplied to the the piston side of the hydraulic cylinder. The piston cannot extend.

Measure the pressures in M1, M2 and M3 and enter the values in Table 08.2.

6. Only when pushbutton S4 is operated additionally is port X of pilot operated check valve item 1.4 controlled via 4/2 directional valve item 1.3 and the check valve opens. Fluid can now flow at zero pressure from the piston rod side via 4/3 directional valve item 1.1 to the reservoir.

Measure the pressures at M1, M2 and M3 during operation and enter the values in Table 08.2.

Caution

While the throttle is open and the piston is lowering, the movement of the piston may be very jerky. The piston can advance due to the load on the vertical cylinder. This causes underpressure in the piston chamber and hence an absence of pilot pressure at port X of the pilot operated check valve, i.e. the valve closes abruptly. When pressure is built up again on the piston side, port X on the check valve is again supplied with pilot pressure. The check valve opens abruptly.

7. Set the lowering speed of the cylinder to a lowering time of approx. 5 s on throttle valve item 1.6.

Caution

Notes

Before converting the circuit for the further execution of the order, switch the hydraulic pump off!

08


10


Measured values M1 p in bar

M2 p in bar

M3 p in bar

Lower cylinder via the pressure relief valve

45

45

70

Lower cylinder via the check valve

20

10

15

Measuring point

Table 08.2 Lowering pressures


08 Caution

After having completed the practical work on the training system, switch the hydraulic pump off! Set the throttle valve and the pressure relief valves to minimum pressure. No pressure gauge may indicate a pressure!

Evaluating the work results with regard to the customer requirement • Fluid can only flow through a hydraulically pilot operated check valve in the checking direction, if it was opened by means of a hydraulic control signal. • The pilot operated check valve can only close, when the pilot line is depressurized. • The pilot operated check valve can only close properly, when the fluid can freely flow away from the closing element. • To prevent decompression shocks during opening of the check valve, components with a pre-opening feature of the main poppet are used (development of theoretical knowledge).

Project 09: Throttle valve, adjustable


Project 09: Throttle valve, adjustable Project/trainer information In hydraulic systems the piston velocity of a hydraulic cylinder or the revving speed of a hydraulic motor should often be adjustable. The flow provided by the hydraulic pump can be controlled with the help of flow control valves. Flow control valves are classified in: Throttle - fine throttle/orifice and flow control valve. In the following Project 09 knowledge is to be imparted with regard to the operating principle and the use of throttle valves. The task of a throttle valves is to offer a flow resistance by changing the flow cross-section. As a result of the pressure drop, Dp across the throttling point, the flow and consequently the speed of the actuator changes. In the project order the trainee is to work out and document the characteristic curve of a throttle. By changing the throttle settings, he/she is to understand that: • the differential pressure Dp rises while the flow increases and the throttling cross-section remains constant, • the differntial pressure Dp rises in proportion to the reduction in the throttling cross-section while the flow remains constant, • the flow is independent of the pressure level when the pressure differential Dp is constant. The control set up on the training system allows the trainee to measure various differential pressures across the throttle valve at certain flows. A load can be simulated by installing a pressure relief valve in the return line of the 4/3 directional valve. Notes on detailed technical information about the throttle valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 13 • Technical data sheet RE 27219 Throttle valve type MG

09



Project definition In the plant of the customer, a conveyor belt, on which unchanged loads are transported, is powered by a hydraulic motor. The drive speed of the hydraulic motor is to be adjustable in both directions of travel. In order that the customer can understand the proposed solution, he requires technical documentation. As an option, he wants to know whether the drive speed changes when loads of different weights are transported.

09

Fig. 09.1 Practical example: Conveyor belt for transporting printed-circuit boards

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a throttle valve (specialist qualification) • Handling of hydraulic components in line with functional needs



Project steps • Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, through the selection of hydraulic components from the data sheet collection (RE 27219 Throttle check valve).

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out and documenting the system parameters requred by the customer.

• Checking:


• Evaluating:

Are there further possibilities of meeting the customer requirement or simpler ways of project execution?

09 Notes




Item 0.2

Item 0.3

Item 1.3

Item 1.0

Item 1.5

Item 1.1

Optional

09

Item 1.4 Load pressure

Item 0.1

Item 1.2

Power unit limit

Fig. 09.2 Hydraulic circuit diagram: Throttle valve, adjustable

Measuring glass




Stop

09







Qty

1.0

1


DM 2.N

1.1

1


DW 13E

1.2/1.4

2


DD 1.1

1.3

1


DF 1.2

2


DZ 4.1

4


DZ 1.4

3


DZ 25

Hose

VSK 1

0.1 - 0.3


1

Stopwatch

1

Flowmeter


Type designation

DFF 1

Symbol

09



Connection block

Measuring glass


D


Fig. 09.4 Recommended component arrangement with component designation for parts list 09.1 and hydraulic circuit diagram Fig. 09.2


Notes

09




Warning

Caution


09





Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn. 4. By actuating push-button S1 solenoid Y1b of 4/3 directional valve Item 1.1 is energized, the hydraulic motor Item 1.0 rotates. Throttling process 1: 5. Close throttle valve Item 1.3. Then open the throttle valve by � turn of the adjustment knob. Marking with a point for the precise adjustment (1st position).



While directional valve Y1b is operated, the load pressure can be adjusted to 20 bar on pressure relief valve Item 1.4, which is installed in the return line of the 4/3 directional valve, and the pressure value read off from pressure gauge M3.

6. The flow measurement can be taken with the help of a measuring glass in liters/time or optionally using flowmeter Item 1.5. Measure the pressure differential ∆p across throttle valve Item 1.3 using pressure gauges M2 and M3 and enter the values in Table 09.2. 7. While the throttle position remains unchanged (1st position) increase the load pressure to 25 bar, 30 bar, 35 bar, 40 bar and 42 bar. Throttling process 2: 8. Throttle valve Item 1.3, � turn opened (2nd position). Follow the instructions in points 6 to 8 and enter the values in Table 09.2. Throttling process 3: 9. Throttle valve Item 1.3, 1� turns opened (3rd position). Follow the instructions in points 6 and 7 and enter the measurement result in Table 09.2.

Caution

After having completed practical work on the training system, switch the hydraulic pump off! Open the throttle valve and set the pressure relief valves to minimum pressure. No pressure gauge may indicate a pressure!

10. Optional: Carry the measured values over in a Diagram 09.1.

Measured values

Throttle Item 1.3 1st position

Throttle Item 1.3 2nd position

Throttle Item 1.3 3rd position

M3 p in bar M2 p in bar M2 - M3 ∆p in bar q in l/min M3 p in bar M2 p in bar M2 - M3 ∆p in bar q in l/min M3 p in bar M2 p in bar M2 - M3 ∆p in bar q in l/min

20

25

30

35

40

50

46

46

47

47

47

48

26

21

17

12

7

2

1.98

1.74

1.47

1.20

0.87

0

20

25

30

35

40

50

44

45

45

46

47

48

24

20

15

11

7

2

3.64

3.22

2.77

2.26

1.71

0

20

25

30

35

40

50

39

41

43

44

45

48

19

16

13

9

5

2

6.40

5.82

5.09

4.20

3.18

0

Table 09.2 Measurement results from execution of the order

09


10



1st position

2nd position

3rd position

Differential pressure ∆p in bar

30 25 20 15 10 5

09

0 0

1

2

3

4

5

6

7

Flow qV in l/min Diagram 09.1 Diagram with measured values

Evaluating the work results with regard to the customer requirement • The customer requirement can be met by means of a throttle valve. • As the flow increases the differential pressure ∆p rises when the throttling cross-section remains constant. • At a constant flow the differential pressure becomes greater, the smaller the throttling crosssection is. • At a constant differential pressure, the flow is independent of the pressure level. • As an optional extra, the customer wishes to implement a velocity adjustment feature for various weights. Since the throttle operates in dependence upon loads, the velocity of the conveyor belt becomes smaller as the load increases (greater weight).

Project 10: Throttle check valve


Project 10: Throttle check valve Project/trainer information If a given velocity is to be adjustable, a throttle valve can be used. If the traversing speed is to be adjustable in only one direction, a throttle check valve is used. Like a throttle valve a throttle check valve is a variable throttle with the disadvantages dealt with in Project 09 such as temperature and dependence on the differential pressure. In the following Project 10 knowledge of the operating principle and the use of a throttle check valve can be imparted. The task of a throttle check valve is to throttle a given flow in only one direction of rotation. The actuator to be controlled moves with flow throttling in one direction and almost unthrottled in the opposite direction. If the throttle is used, for example, on a single-rod cylinder, meter-in or meter-out throttling can be provided. In the project order, the trainee is to get familiar with the typical characteristics of a meter-in or meter-out throttle. By installing the throttle valve differently, he/she is to understand that: • a throttle check valve is a combination of a throttle and a check valve • with a throttle check valve the piston velocity of a single-rod cylinder can be adjusted in only one direction, • in the case of meter-out throttling the single-rod cylinder is hydraulically isolated, but pressure intensification can occur on the piston rod side, • the use of a meter-in throttle can result in jerky movements of the single-rod cylinder (slip stick). On the basis of the control set up on the training system for powering a horizontally installed single-rod cylinder, the trainee can recognize the pros and cons of meter-in and meter-out throttling by taking measurements on the piston and on the piston rod side. Notes on detailed technical information about the throttle check valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 13 • Technical data sheet RE 27219/throttle check valve, type MK Technical data sheet RE 27506/double throttle check valve, type Z2FS

10



Project definition In a machining station (bending of a roll seam) the hydraulic advance velocity is to be adjustable. The return stroke is to be performed at maximum velocity. As in Project 09, the customer requires technical documentation in order to be able to understand the proposed solution. In addition, measurements of meter-in and meter-out throttling are required.

10

Fig. 10.1 Practical example: Tool advance for roll seam bending

Project tasks • Independent understanding and solving of the task set by applying hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a throttle check valve (specialist qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing the customer order with the help of, among others, the technical data sheets RE 27219 and RE 27506.

• Deciding:


• Executing:


• Checking:


• Evaluating:


10 Notes



Hydraulic circuit diagram 1 Item 1.0

Item 0.2

Item 0.3

Item 1.3

Item 1.1

10 Item 0.1

Item 1.2

Power unit limit

Fig. 10.2 Hydraulic circuit diagram: Meter-in throttle - extending a single-rod cylinder

Measuring glass




Item 0.2

Item 0.3

Item 1.3

Item 1.1

10 Item 0.1

Item 1.2

Power unit limit

Fig. 10.3 Hydraulic circuit diagram: Meter-out throttle - extending a single-rod cylinder

Measuring glass




Item 0.2

Item 0.3

Item 1.3

Item 1.1

10 Item 0.1

Item 1.2

Power unit limit

Fig. 10.4 Hydraulic circuit diagram: Meter-in throttle - retracting a single-rod cylinder

Measuring glass




Item 0.2

Item 0.3

Item 1.3

Item 1.1

10 Item 0.1

Item 1.2

Power unit limit

Fig. 10.5 Hydraulic circuit diagram: Meter-out throttle - retracting a single-rod cylinder

Measuring glass




Stop

10


Fig. 10.6 Wiring diagram for hydraulic schematic diagrams Fig. 10.2 to 10.5





Qty


Type designation

1.0

1


1.1

1


DW 13E

1.2

1


DD 1.1

1.3

1


DF 2.2

Symbol

ZY 1.3

10

0.1 - 0.3

1


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

Table 10.1 Parts list for hydraulic circuit diagrams 10.2 to 10.5


10


Connection block

Measuring glass

Component arrangement 1

D


Fig. 10.7 Recommended component arrangement with component designation for parts list Table 10.1 and hydraulic circuit diagram 10.2


Notes

10


11


Connection block

Measuring glass


D




Notes

10


12


Connection block

Measuring glass


D




Notes

10


13


Measuring glass


Connection block

��

D


Fig. 10.10 Recommended component arrangement with component designation for parts list Table 10.1 and hydraulic circuit diagram 10.5


Notes

10


14



Warning

Caution


Execution of the order Set up the controls as described in the following: 1. Mount the components required according to Table 10.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn. Task 1

Meter-in throttle: Piston side → extending 4. Adjust throttle check valve Item 1.3 so that the piston of the single-rod cylinder extends within 5 s; to this end operate push-button S2. Enter the pressure values (during extending) on piston side M2 and on piston rod side M3 in Table 10.2.

10


15


Before making any conversion for further order processing, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 2

Meter-out throttle: Piston rod side → extending 5. Convert the hydraulic control according to Hydraulic circuit diagram Fig. 10.3, observing the safety notes given under point 1. Repeat working steps 2 and 3. 6. Adjust throttle check valve Item 1.3 so that the piston of the single-rod cylinder extends within 5 s. To this end actuate push-button S2. Enter the pressure values (during extending) on piston side M2 and on piston rod side M3 in Table 10.2. Before making any conversion for further order processing, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 3

Meter-out throttle: Piston rod side ← retracting 7. Convert the hydraulic control according to Hydraulic circuit diagram Fig. 10.4, observing the safety notes given under point 1. Repeat working steps 2 to 4. 8. Adjust throttle check valve Item 1.3 so that the piston of the single-rod cylinder retracts within 5 s. To this end first operate push-button S2 for extending and then for the adjustment of the throttle operate push-button S4 for retracting. Enter the pressure values (during retracting) on piston side M2 and on piston rod side M3 in Table 10.2. Before making any conversion for further order processing, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 4

Meter-out throttle: Piston side ← retracting 9. Convert the hydraulic control according to Hydraulic circuit diagram Fig. 10.5, observing the safety notes given under point 1. Repeat working steps 2 and 3. 10. Adjust throttle check valve Item 1.3 so that the piston of the single-rod cylinder retracts within 5 s. To this end first operate push-button S2 for extending and then for the adjustment of the throttle operate push-button S4 for retracting. Enter the pressure values (during retracting) on piston side M2 and on piston rod side M3 in the table of measured values.

Caution

After having completed practical work on the training system switch the hydraulic pump off! No pressure gauge may indicate a pressure! Open the throttle check valve.

10


16


Measured values M2 p in bar

M3 p in bar

Meter-in throttle, piston side → extending

2

3

Meter-out throttle, piston rod side → extending

50

77

Meter-in throttle, piston rod side ← retracting

2

4

Meter-out throttle, piston side ← retracting

27

50

Measuring points →

Table 10.2 Measurement results from the execution of the order

The measurement results were obtained at an oil temperature of approx. 20 °C. The values measured by the trainees can deviate by 10 %.

Warning

Safety note from accident prevention regulations: If there is a riks of pressure intensification on the piston rod side, protection must be provided in the form of an additional pressure relief valve. Setting: 10 % above system pressure; the system operator must secure the setting against unauthorized changes by providing a lead seal.

Evaluating the work results with regard to the customer requirement • The customer requirement can be met by means of a throttle check valve, i.e. the traversing speed of the advance carriage is adjustable in one direction. • A throttle check valve is a combination of devices comprising a throttle valve and a check valve. • The advance cylinder can be hydraulically isolated during extended, but on the piston rod side there is a risk of pressure intensification. Depending on the area ratio of the single-rod cylinder the intensified pressure can reach, e.g. 2 : 1, which is the double system pressure. • To provide protection against pressure intensification a pressure relief valve can be installed. • The flow through a throttle check valve depends on the differential pressure ∆p.

10

Project 11: Flow control valve


Project 11: Flow control valve Project/trainer information If the velocity of a hydraulic cylinder or the speed of a hydraulic motor is to be kept constant independently of pressure fluctuations, a flow control valve is used, e.g. in conjunction with a hydraulic cylinder, which is to lift and lower different loads, but is to move at the same traversing velocity. A flow control valve comprises a control loop and consists of an adjustable orifice and an upstream or downstream pressure compensator. Due to a continuous comparison of the pressures upstream and downstream of the adjustable orifice, the set flow is kept constant. In the following Project 11 you can impart knowledge of the operating principle and use of flow control valves. The task of the flow control valve used is to maintain the speed of a hydraulic motor constant despite varying loads. In the project order, the trainee has to work out and record the characteristic curves of a 2-way flow control valve. By making various adjustments to the flow control valve and changing the loads on the hydraulic motor, he/she is to recognize that: • the flow remains constant at varying load pressures, • at varying inlet pressures, the flow remains constant, • a flow control valve features a closed hydraulic control loop, • flow qV eff. drops below a minimum pressure differential. With the help of the control set up on the training system for driving a hydraulic motor, the trainee can recognize the different flow rates under changing loads. The load can be simulated with the help of a pressure relief valve installed in the return line of the 4/3 directional valve. Notes on the detailed technical information about the flow control valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, chapter 13 • Technical data sheet RE 28163/2-way flow control valve

11



Project definition In a machining station, a hydraulic rotary drive is to swivel a drum from the horizontal to the vertical position after a welding process. The movement is to be performed by a hydraulic motor. Despite varying loads, the motor speed must remain constant. Applying the knowledge that was gained in Project 09, a load-independent throttle valve is to be used in the velocity control. In order that the customer can understand the solution, he requires, apart from the technical documentation for the use of different workpiece weights, a flow/pressure differential curve for varying loads and falling system pressures.

11

Fig. 11.1 Practical example: Rotary drive for workpiece relocation

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for a flow control valve (technical qualification) • Handling of hydraulic components in line with functional needs



Project steps

Notes

• Informing:


• Planning:

Planning and organizing the execution of the customer order; among others, by dealing intensively with data sheet RE 28163.

• Deciding:

Using the sketches of the circuit diagrams from Project 10: Throttle check valve, selection of the relevant sketch with selection of the hydraulic components.

• Executing:

Set-up of the hydraulic control on the training system and preparation and documentation of the system parameters requested by the customer.

• Checking:


• Evaluating:


11




Item 0.2

Item 0.3 Item 1.3

Item 1.0

Item 1.1 Item 0.4 Item 1.4 Load pressure

11 Item 0.1

Item 1.2

Power unit limit

Fig. 11.2 Hydraulic circuit diagram: Load-independent speed control of a tool spindle

Measuring glass




Stop

11







Qty


Type designation

1.0

1


DM 2.N

1.1

1

4/3 directional valve direct operated by two solenoids, spring centring of the central position and central position P, T, A, B

DW 13E

1.2/1.4

2


DD 1.1

1

2-way flow control valve, adjustable, for one direction of flow, largely independent of viscosity and pressure diferential, adjustable, with by-pass check valve

DF 3

1.3

0.1 - 0.4

11

4


DZ 1.4

4

Hose with quick-release coupling, with check valve

DZ 25.1

Hose 1

Stopwatch

Table 11.1 Parts list for hydraulic circuit diagram 11.2

Symbol

VSK 1



Connection block

Measuring glass


D


Fig. 11.4 Recommended component arrangement with component designations to parts list Table 11.1 and hydraulic circuit diagram Fig. 11.2


Notes

11



Safety notes To ensure the operability of plant and machinery, and consequently to allow the recognition of potential risks, safety regulations must be observed before and during the execution of the order. Relevant sources of regulations are given in the introduction of the present manual. If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life. Warning

Caution

Before starting work on the training stand, make sure that electrical ON/OFF switches on the hydraulic power unit are pressed in, that is, that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy at rest. This can cause injury when the system is opened.

Execution of the order Set up the controls as described below: 1. Hang the components required according to Table 11.1 in a clearly arranged manner into the training system according to the prepared circuit diagram.


For connections, to which pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25.1. Hand-tighten the pressure gauge measuring lines hand tight at the relevant minimess connection of the hydraulic hose.


Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. Task 1

Determining the flow/pressure differential curve with rising load pressure 3. Set the system pressure on pressure relief valve item 1.2 to 45 bar. 4. Turn flow control valve item 1.3 to scale position 2. 5. Operate pushbutton S4; the hydraulic motor rotates clockwise; adjust the load pressure on pressure relief valve item 1.5 in the return flow line to 10 bar (pressure gauge M4). Enter the pressure values M2 (upstream of DF 3) and M3 (downstream of DF 3) in measurement table 11.2. Calculate the pressure differential Dp (M2 - M3) and enter it in the measurement table.

11



Flow measurement by means of the measuring glass as a function of time or optionally using flowmeter DZ 30.

6. Stepwise increase (in 5 bar increments) the load pressure on the hydraulic motor by means of pressure relief valve item 1.5 in the return flow line to 40 bar and enter the pressure values M2, M3, the Dp and flow qV in Table 11.1. 7. Turn flow control valve item 1.3 to scale position 4. 8. Repeat order steps 5 to 6 and enter the measured values in Table 11.2.

Measured values Measuring point M2 p in bar

M3 p in bar

Pressure differential Dp in bar

Flow qV in l/min

Scale position 2

Scale position 4

Load pressure

Scale position 2

Scale osition 4

Scale position 2

Scale position 4

42

40

10

32

30

0.47

1.92

42

40

15

27

25

0.47

1.92

42

40

20

22

20

0.46

1.90

42

40

25

17

15

0.46

1.90

42

40

30

12

10

0.45

1.86

42

40

35

7

5

0.31

1.30

42

42

40

2

2

0

0

11

Table 11.2 Values measured during the execution of the order, increasing load pressure

The values were measured at an oil temperature of approx. 20 °C. The values measured by trainees can deviate by 10 %. Scale position 2

Scale position 4

2,5

Flow qV in l/min

2 1,5 1 0,5 0 0

5

10

15

20

25

Pressure differential Dp in bar Diagram 11.1 Flow/pressure differential curve, increasing load pressure

30

35

40


Task 2

10


Determining the flow/pressure differential curve at varying system pressure 9. Set pressure relief valve item 1.5 in the return flow line (load pressure) to minimum (spring unloaded). 10. Set the system pressure on pressure relief valve item 1.2 to 40 bar. 11. Turn flow control valve item 1.3 to scale position 2. 12. Operate pushbutton S4; the hydraulic motor rotates clockwise. Enter pressure values M1 (upstream of DW 13E) and M3 (downstream of DF3) in Table 11.3. Calculate the pressure differential Dp (M1 - M3) and enter the value in the measurement table.

Flow measurement by means of the measuring glass or optionally by means of flowmeter DZ 30. Enter flow qV in Table 11.3.

13. Stepwise reduce (in 5 bar increments) the system pressure by means of pressure relief valve item 1.2 down to the minimum pressure of 10 bar.

Caution

After completion of the practical work on the training system, switch the hydraulic pump off! Set the throttle valve and pressure relief valves to minimum pressure. No pressure gauge may indicate a pressure!

Measured values Measuring point M1 Measuring point M3 Pressure differential p in bar p in bar Dp in bar

Flow qV in l/min

40

5

35

0.5

35

5

30

0.5

30

5

35

0.5

25

5

20

0.5

20

5

15

0.5

15

5

10

0.5

10

5

5

0.4

Table 11.3 Falling system pressure

The results above were measured at an oil temperature of approx. 20 °C. The values measured by trainees can deviate by 10 %.

11


11


0,6

Flow qV in l/min

0,5

0,4 0,3 0,2

0,1 0 0

10

15

20

25

30

35

40

Pressure differential ∆p in bar Diagram 11.2 Flow/pressure differential curves, system pressure falling

11

Evaluating the work results with regard to the customer requirement • At a varying load pressure, flow qV remains largely constant. • At varying inlet/system pressure, flow qV remains largely constant. • In terms of construction, the flow control valve consists of an adjustable orifice and a pressure compensator, which creates a constant ∆p across the orifice; the flow control valve features a closed hydraulic control loop. • Below a minimum pressure differential (manufacturer-specific) flow qV drops.


12


Notes

11

Project 12: Pressure relief valve, direct operated


Project 12: Pressure relief valve, direct operated Project/trainer information If the operating pressure/system pressure is to be limited to an adjustable maximum value in a hydraulic system, a pressure relief valve is used. We differentiate pressure relief valve by: Pressure relief valves, direct operated and pilot operated. The limitation of the system pressure protects system components such as pipes and hoses, connections, control blocks, pump housings, etc. against destruction. Pressure relief valves are also used to provide protection against, e.g. pressure peaks. In the special machinery construction sector, e.g. in presses, pressure relief valves are also used as load holding valves. To be able to assess the characteristics of a direct operated pressure relief valve, the characteristic curves of the pressure/flow relation must be known. In the following Project 12 knowledge of the operating principle, use and adjustment options of direct operated pressure relief valves is to be gained. Pressure relief valves are used to limit the system pressure of a hydraulic control. In the project order, the trainee is to get to know the characteristic curves of a direct operated pressure relief valve. By making various settings on the pressure relief valve, he/she is to recognize that: • the characteristic curve of a pressure relief valve shows the dependence of pressure p on flow qV; • despite an open pressure relief valve a resistance (line and valve resistance) can be observed; • in the case of a parallel connection of throttle and pressure relief valves the flow is divided; • pressure relief valves can be used, for example, as overload protection. On the basis of the set up control the trainee can work out the characteristic curves of a pressure relief valve by changing the system pressure and the resistance installed in parallel. The resistance is provided by an adjustable throttle valve. Notes on detailed technical information about the direct operated pressure relief valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 12 • Technical data sheet RE 25402/Pressure relief valve, direct operated

12



Project definition On a lifting platform, the system pressure is to be reduced due to the use of lower weights. The new setting is to save energy. The customer requires work instructions in order that he can adjust the pressure without requiring expert help. Moreover, he is interested in the pressure/flow relationship characteristic curves of pressure relief valves.

12

Fig. 12.1 Practical example: Pressure relief valves

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a pressure relief valve (specialist qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing the customer order, among others, by dealing intensively with technical data sheets RE 25402.

• Deciding:


• Executing:


• Checking:


• Evaluating:


Notes

12




Item 1.1

Item 1.5

Item 0.1 Item 1.0

Power unit limit

Fig. 12.2 Hydraulic circuit diagram: Determination of technical data of a pressure relief valve, direct operated

Measuring glass

12




Qty


Type designation

1.0

1


DD 1.1

1.1

1


DF 1.2

1


DZ 4.1

1


DZ 1.4

1


DZ 25

Hose

VSK 1

0.1

1

Stopwatch

1

Flowmeter


DZ 30

Symbol

12



Connection block

Measuring glass


D




Notes

12




Warning

Caution


Execution of the order Set up the control as described below: 1. Mount the components required according to the parts list in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution


An electrical control is not required for this experiment set-up.

Relationship between flow and pressure relief valve 2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Close throttle valve Item 1.1, set the system pressure to 30 bar on pressure relief valve Item 1.0. Measure the flow through the measuring glass as a function of time or optionally using flowmeter Item 1.2 (DZ 30).

Enter the values in Table 12.2.

12



4. Open throttle valve Item 1.1 in individual steps (5 bar increments). The pressure is shown on pressure gauge M1. Enter the M1 measurement results and flow qV in Table 11.2. 5. Carry over the measurement results from Table 12.2 to Diagram 12.1. After having completed practical work on the training system switch the hydraulic pump off! No pressure gauge may indicate a pressure! Open the throttle check valve. Caution

Measured values

Throttle valve

System pressure M1 p in bar

Flow qV in l/min through pressure relief valve

Closed

30

7.6

25

4.3

20

1.8

15

0

10

0

Open

Table 12.2 Measured values: Pressure relief valve - pressure/flow


12



35

System pressure M1 p in bar

30 25 20 15 10 5 0 0

1

2

3

4

5

6

7

8

Flow qV across the pressure relief valve in l/min Diagram 12.1 Pressure/flow characteristic curves, falling system pressure

Evaluating the work results with regard to the customer requirement • The characteristic curve of the pressure relief valve shows the dependence of pressure p on flow qV. • When the throttle valve is open or the pressure relief valve is open, a resistance can be measured, which can be traced back to line resistances and the valve resistance. • Due to the interaction of the throttle valve and the pressure relief valve the flow is divided. • Pressure relief valves are mainly used as overload protection for limiting the maximum pressure.

12


10


Notes

12

Project 13: Pressure relief valve control


Project 13: Pressure relief valve control Project/trainer information If three different pressures are to be realized in a hydraulic circuit, pressure relief valves

connected in series or in parallel

can be used for this purpose. The following Project 13 can be used to acquire knowledge of the practical use and adjustment options of direct operated pressure relief valves. In the project order, the trainee has to develop and record the adjustment options of parallel and series circuits with the help of experiment set-ups on the training system. As preparation to the practical experiment, the trainee has to become familiar with the theoretical principles of the circuits. By controlling the pressure relief valves in different ways by means of a 4/3 directional valve, he/she is to recognize that: • Pressure relief valves can be used for pre-selecting various system and pilot pressures via pressure stage circuits, • in the case of pressure relief valves controlled in parallel, the lowest set pressure becomes effective, • in the case of pressure relief valves controlled in series, the pressures add up. With the help of the controls set up on the training system, the trainee is to understand the typical features of the controls by operating pressure relief valves connected in parallel and in series. With the help of a 4/3 directional valve he/she can control pressure relief valves optionally connected in parallel or in series. Notes on the detailed technical information about the direct operated pressure relief valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, chapter 12 • Technical data sheet RE 25402/Pressure relief valve, direct operated

13



Project definition On a punching rig, three, electrically controllable pressures are to be callable for different tools and different working sequences. The customer wishes solution proposals for the simple realization of a pressure control and requires technical documentation with the necessary system parameters.

13 Fig. 13.1 Practical example: Punching equipment

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for a pressure relief valve (technical qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing the execution of the customer order, among others, by dealing intensively with data sheet RE 25402.

• Deciding:


• Executing::


• Checking:


• Evaluating:


Notes

13



Hydraulic circuit dagram 1

Item 0.3 Item 1.2

Item 0.2 Item 1.1

Item 1.0

Measuring glass

Item 0.1

13 System

Power unit limit

Fig. 13.2 Hydraulic circuit diagram: 3-stage pressure circuit



Hydraulic circuit diagram 2

Item 0.3 Item 1.2

Item 0.2 Item 1.1

Item 1.0

Measuring glass

Item 0.1

13 System

Power unit limit

Fig. 13.3 Hydraulic circuit diagram: Parallel pressure circuit



Hydraulic circuit diagram 3

Item 0.2

Item 0.3 Item 1.1

Item 1.2

Item 1.0

Measuring glass

Item 0.1

System

Power unit limit

Fig. 13.4 Hydraulic circuit diagram: Series pressure circuit

13




Circulation

13

Control 4/3 directional valve Solenoid “a”

Fig. 13.5 Wiring diagram for hydraulic circuit diagrams Fig. 13.2 and 13.4

Solenoid “b”




Qty


Type designation

1.0

1

4/3 directional valve with direct operated by two solenoids, spring centring of the central position and central position P - T, A, B

DW 4E

1.1/1.2

2


DD 1.1

2

Distributor plate with four connections

DZ 4.1

3

Pressure gauge with hose and quick-release coupling without check valve

DZ 1.4

3

Hose with quick-action coupling, with check valve

DZ 25

Hose

VSK 1

0.1 - 0.3

Table 13.1 Parts list for hydraulic circuit diagrams Fig. 13.2 to 13.4

Symbol

13



Connection block

Measuring glass


D


Fig. 13.6 Recommended component arrangement with component desgnations for parts list Table 13.1 and hydraulic circuit diagram Fig. 13.2


Notes

13


10


Connection block

Measuring glass


D




Notes

13


11


Connection block

Measuring glass


D




Notes

13


12


Safety notes To ensure the operability of plant and machinery, and consequently to allow the recognition of potential risks, safety regulations must be observed before and during the execution of the order. Relevant sources of regulations are given in the introduction of the present manual. If work on electrohydraulic components is carried out improperly, risks of injury and a safety risk can arise during operation of the system, including danger to life. Warning

Caution

Before starting work on the training stand, make sure that electrical ON/OFF switches on the hydraulic power unit are pressed in, that is, that the system is switched off. Check on the system pressure gauge that the system is depressurized. Hydraulic systems can store pressure energy at rest. This can cause injury when the system is opened.

Execution of the order Set up the control as described below: 1. Hang the components required according to the parts list in a clearly arranged manner into the training system according to the prepared circuit diagram.


For the connections, to which the pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25. Hand-tighten the pressure gauge line hand tight to the relevant minimess connection of the hydraulic hose.


Warning

Caution

Task 1

Make sure that pipes or hoses are connected to all connections - in this case also to minimess lines or that the connections are plugged by means of plug screws or protective caps. Leakage oil may drip through open connections and cause a slipping risk. Before commissioning the hydraulic control, i.e. before switching the hydraulic pump on, check, whether all pressure control valves are set to minimum pressure (spring unloaded) and all throttle valves are open.

Wire the electrical control according to wiring diagram 13.5.

Check the pressure set on the control pump of the drive power unit and, if required, correct it to 50 bar.

3-stage pressure circuit 2. Switch the hydraulic pump and check the set up control for leakage. No pressure gauge may indicate a pressure. 3. Operate directional valve item 1.0 by actuating pushbutton S4. Set the system pressure on pressure relief valve item 1.1 at port B to 15 bar (pressure gauge M2).

13


13


4. Operate directional valve item 1.0 by actuating pushbutton S2. Set the system pressure on pressure relief valve item 1.2 at port A to 20 bar (pressure gauge M3).

Enter the measured values (pressure gauge M1, M2, M3) in Table 13.2. Before converting the circuit for the further execution of the order, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 2

Parallel circuit 5. Connect the hydraulic control according to circuit diagram Fig. 13.3 by means of hoses. Do not change the pressures set on pressure relief valves item 1.1 and item 1.2! 6. Operate directional valve item 1.0 by actuating pushbutton S2.

Enter the measured values (pressure gauges M1 and M2) in Table 13.3. Before converting the circuit for the further execution of the order, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 3

Series circuit 7. Connect the hydraulic control according to circuit diagram Fig. 13.4 by means of hoses. Do not change the pressures set on pressure relief valves item 1.1 and item 1.2! 8. Operate directional valve item 1.0 by actuating pushbutton S2.

Enter the measured values (pressure gauges M1, M2, M3) in Table 13.4.

Caution

Notes

After completion of the practical work on the training system, switch the hydraulic pump off! No pressure may indicate a pressure! Open the throttle check valve.

13


14


Measured values Spool position DW 4E

Measuring point M1 Measuring point M2 Measuring point M3 p in bar p in bar p in bar

0

8

0

0

a

23

0

20

b

18

15

0

Table 13.2 3-stage pressure circuit

Spool position DW 4E

Measuring point M1 p in bar

Measuring point M2 p in bar

0

8

0

a

18

15

Table 13.3 Parallel pressure circuit

Spool position DW 4E

Measuring point M1 Measuring point M2 Measuring point M3 p in bar p in bar p in bar

0

8

0

0

a

38

35

20

Table 13.4 Series pressure circuit


Evaluating the work results with regard to the customer requirement • In a 3-stage pressure circuit, direct operated pressure relief valves can be controlled via a directional valve and consequently three different, pre-selected system pressures can be realized. • In the case of pressure relief valves connected in parallel, the lowest pressure set is effective. • In the case of pressure relief valves connected in series, the set pressures add up.

13

Project 14: Pressure reducing valve


Project 14: Pressure reducing valve Project/trainer information If a secondary actuator in a hydraulic control is to be controlled at a lower pressure independently of the system pressure, a pressure reducing valve is used. In contrast to the pressure relief valve, which limits the input pressure, the pressure reducing valve influences the output pressure (actuator pressure). The pressure that can be set on a pressure reducing valve is always lower than the system pressure. The following Project 14 is intended to impart knowledge of the operating principle and the use of a pressure reducing valve. The task of a pressure reducing valve is to keep the output pressure constant and lower than the input pressure. In the project order the trainee is to get familiar with the typical characteristics of a pressure reducing valve with the help of a practice-oriented experiment set up on the training system. This project task is to help him/her understand that: • with the help of a pressure reducing valve a secondary actuator can be controlled at a pressure which is lower than the system pressure, • excess pressure in port A is discharged via port T of the pressure reducing valve to the tank, • a pressure reducing valve without by-pass check valve operates as pressure relief valve when controlled via port A. The control set up on the training system (two actuators are controlled simultaneously at different pressures via a 4/3 directional valve) is to make the characteristics of a 3-way pressure reducing valve clear to the trainee. Notes on detailed technical information about the pressure reducing valve: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 12 • Technical data sheet RE 26564 Pressure reducing valve, direct operated

14



Project definition In Project 11 a workpiece is to be swiveled by a hydraulic motor in a machining station. In a further step of the project the same workpiece is to be clamped at reduced pressure. In order that the hydraulic motor only starts to rotate after clamping is completed, it is to be hydraulically pre-loaded. The customer wishes a solution with which the control can easily be realized and requires the associated technical documentation with the necessary system parameters. In addition, he needs information about the setting options and wants to know, why a by-pass check valve is required.

14 Fig. 14.1 Practical example: Swiveling/clamping unit

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a pressure reducing valve (specialist qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing of the customer order by, among others, dealing intensively with technical data sheet RE 26564.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Preparation and documentation of the measured data.

• Checking:


• Evaluating:


Notes

14




Item 2.0 Rotate

Clamp

Item 0.3

Item 1.3

Item 0.2 Item 2.1

Item 1.4

Item 1.1

Item 0.1 Item 1.2

Measuring glass

14 Power unit limit

Fig. 14.2 Hydraulic circuit diagram: Machine tool control




Stop

14


Retraction Extension -Single-rod cylinderClockwise rotation -Hydraulic motor-





Qty

1.0

1


ZY 1.3

2.0

1

Fixed displacement motor with exteral leakage oil lines and two directions of rotation

DM 2.N

1.1

1


DW 13E

1.2/2.1

2


DD 1.1

1.3

1

3-way pressure reducing valve

1


DS 2.1

3


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

1.4

0.1 - 0.3



Type designation

Symbol

DD 2

14



Connection block

Measuring glass


D




Notes

14




Warning

Caution



Connect the hydraulic control according to hydraulic circuit diagram Fig. 14.2 by means of hoses. Observe installation direction of check valve Item 1.4! Warning

For the connections, to which pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25. Hand-tighten the pressure gauge measuring lines at the relevant minimess connection of the hydraulic hose.


Warning

Caution



14


Task 1


Control with by-pass check valve 2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure.

Set the system pressure on pressure relief valve Item 1.2 to 50 bar plus one turn.

3. Actuate push-button S4 to operate directional valve Item 1.1. Hydraulic motor Item 2.0 rotates clockwise; set pressure relief valve Item 2.1 on the hydraulic motor (port B) to a load pressure of 40 bar (pressure gauge M2). 4. Set the clamping pressure to 20 bar on pressure reducing valve Item 1.3.

Enter the values measured during extending and retracting of the advance cylinder piston (pressure gauge M1, M2, M3) in Table 14.2.

Also enter the pressures in the extended and retracted condition. Before making any conversion for further order processing, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 2

Control without by-pass check valve 5. Modify the hydraulic control. To this end remove by-pass check valve Item 1.4 and the two connection hoses.

Do not change the load pressure on hydraulic motor Item 2.0 and the pressure on clamping cylinder Item 1.0.

6. Actuate push-button S4 to operate directional valve Item 1.0. The hydraulic motor rotates against the load pressure of 40 bar, and the clamping cylinder clamps at a pressure of 20 bar. 7. Enter the values measured during extending and retracting of the clamping cylinder piston (pressure gauge M1, M2, M3) in Table 14.2.

Also enter the pressures in the extended and retracted condition.

Note: When the clamping piston retracts after operation of push-button S2 the cylinder moves against a clamping pressure of 20 bar provided via port A of the pressure reducing valve. In this case, the pressure reducing valve assumes a pressure relief function.

Caution


14


10


Measured values

Measuring point →

With by-pass check valve DS 2.1

Without by-pass check valve DS 2.1

M1 p in bar

M2 p in bar

M3 p in bar

M1 p in bar

M2 p in bar

M3 p in bar

Clamping cylinder extending →

20

15

3

20

15

3

Clamping cylinder extended →

45

40

20

45

40

20

Clamping cylinder retracting ←

45

15

20

48

0

26

Clamping cylinder retracted ←

50

0

0

50

0

0

Table 14.2 Values measured on the pressure reducing valve


Evaluating the work results with regard to the customer requirement • A pressure reducing valve can supply a secondary actuator with a lower pressure than the system pressure. • The system pressure must always be higher than the secondary pressure. • When the pressure rises in port A of the pressure reducing valve (e.g. pressure peaks/ changes in the load by the secondary actuator), the pressure increase is reduced to the tank via port T of the pressure reducing valve. • When controlled via channel A, a pressure reducing valve operates as pressure relief valve. • When controlled from T to P the pressure relief valve on the hydraulic motor operates as check valve.

14

Project 15: Pressure switch


Project 15: Pressure switch Project/trainer information If a control signal is to be switched in dependence upon a pressure, pressure switches are used. These are subdivided into: Bourdon tube, piston-type and electronic pressure switches. Bourdon tube and piston type pressure switches are hydro-electrical switches. Electronic pressure switches are a combination of a pressure transducer, an indicator and a threshold switch. The switching elements integrated in a piston-type pressure switch make or break an electrical circuit. In the following Project 15 knowledge can be imparted with regard to the operating principle and use of a piston-type pressure switch. Pressure switches assume switching and monitoring functions in a hydraulic control. In the project order the trainee is to get familiar with the typical characteristics and the setting options of a piston-type pressure switch with the help of a practice-oriented experiment set-up on the training system. The following knowledge is to be gained with this project task: • Piston-type pressure switches issue an electrical control signal. • The hydraulic pressure is used to switch an electrical signal via a micro-switch. • In the case of a piston-type pressure switch the pressure must exceed or fall below the set value in order that a switching process in initiated. Based on the control set up on the training system the trainee is to understand the possible applications of a piston-type pressure switch. A cylinder is to be controlled by means of a 4/2 directional valve, and the pressure on the piston side controlled by a piston-type pressure switch. When the set pressure is reached, the return stroke is to be initiated. Notes on detailed technical information about the piston-type pressure switch: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 15 • Technical data sheet RE 50060 Hydro-electrical pressure switch

15



Project definition Two hydraulic workpieces are to be pressed together in a fixture by means of a hydraulic cylinder. After the pressing pressure was reached, the hydraulic cylinder is to retract automatically. The pressing velocity is to be adjustable. The customer wishes to obtain a proposed solution for an automatic, hydraulic pressing process. In the event of a fault of pressure monitoring, it should be possible to release the pressing fixture electrically. The customer also wants to know the settable minimum pressing pressure. For his technical documentation, the customer requires a circuit diagram with parts list and functional description.

Fig. 15.1 Practical example: International pressure indications on pressure switches for system monitoring

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a piston-type pressure switch (specialist qualification) • Handling of hydraulic components in line with functional needs

15





• Planning:

Planning and organizing of the customer order by, among others, dealing intensively with technical data sheet RE 50060.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out the setting options of the pressure switch at different, given system pressures.

• Checking:


• Evaluating:


Notes

15



Hydraulic circuit diagram Item 1.0 Item 0.2

Item 1.3

Item 1.4

Item 0.3

Item 1.1

Item 0.1 Item 1.2

Power unit limit

Fig. 15.2 Hydraulic circuit diagram: Pressure switch

Measuring glass

15




15 Control 4/2 directional valve Extension -Single-rod cylinderNote: Retracting of the single-rod cylinder can additionally be controlled by means of push-button S1.

Fig. 15.3 Wiring diagram for hdraulic circuit diagram Fig. 15.2




Qty

1.0

1


ZY 1.3

1.1

1


DW 3E

1.2

1


DD 1.1

1.3

1


DD 6E.1

1.4

1


DZ 2.2

1


DZ 4.1

3


DZ 1.4

hose with quick release coupling with check valve

DZ 25

Hose

VSK 1

0.1 - 0.3

3



Type designation

Symbol

15




��

��

��

��

��

��

�

��

��

D

�

�

�

��

��

�

Connection block

�

Measuring glass

��

�


��

��



Notes

15




Warning

Caution



Connect the hydraulic control according to hydraulic circuit diagram Fig. 15.2 by means of hoses. Observe direction of installation of the throttle check valve! Danger



Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure.

Set the system pressure to 30 bar on pressure relief valve Item 1.2.

Set piston-type pressure switch Item 1.3 to maximum by turning the setscrew completely in using an Alllan key 10 A/F.

15



3. Check that the pressing cylinder extends and retracts correctly while the throttle check valve is open. Actuate push-button S2 to operate directional valve Item 1.1. Adjust the extension velocity of the pressing piston to a forward speed of 0.05 m/s by means of throttle check valve Item 1.4. To this end, calculate the velocity as a function of the measured extension time and the stroke length. 4. Adjust the pressing pressure on piston-type pressure switch Item 1.3 (release spring) so that the pressing cylinder piston retracts automatically. To this end, extend the pressing piston to the end position. 5. Set the pressures given in Table 15.2 and verify whether the cylinder retracts automatically.

Enter the results in Table 15.2.

Measured values Pressure relief valve p in bar

Retracts automatically Yes/no

20

No

28

No

30

Yes

32

Yes

40

Yes

Table 15.2 Pressure monitoring of the hydraulic cylinder


Caution


Evaluating the work results with regard to the customer requirement • Piston-type pressure switches output an electrical signal. • The hydraulic pressure is used to switch an electrical signal by means of a micro-switch. • In the case of a piston-type pressure switch, the pressure must exceed or fall below the set value in order to initiate a switching process.

15


10


Notes

15

Project 16: Pressure switch hysteresis


Project 16: Pressure switch/hysteresis Project/trainer information If pressures are to be processed as signals in a hydraulic control, pressure switches must be used. A pressure switch is a converter, which converts an incoming hydraulic pressure into an electrical signal. The switching elements installed in a pressure switch close or open an electric circuit. The switching point at increasing pressure and at falling pressure varies due to friction. The difference in the values is called hysteresis (Greek hysteros: later). P SP rP

1 0 1 0

Hysteresis

Hno (normally open) Hnc (normally closed)

Diagram 16.1 Hysteresis

Adjustable hysteresis on electronic pressure switches Hysteresis maintains the switched state of the output stable, when the system pressure fluctuates around the command value. While the system pressure rises, the output switches when the switching point (SP) is reached; when the system pressure falls again, the output only switches when the reset point (rP) is reached. On electronic pressure switches, the hysteresis is adjustable: Firstly the switching point is determined, then the reset point at the desired distance. In the following Project 16 knowledge can be imparted of the practical effects of hysteresis on a piston-type pressure switch. In the project order the trainee is to get familiar with the hysteresis of a piston-type pressure switch through a practical experiment set-up on the training system. Through this project task, the trainee is to gain the following knowledge: • A piston-type pressure switch always has a hysteresis. • Hysteresis is the difference of switching points at rising and falling pressure. • Hysteresis can have different amounts, which can be attributed to the individual design. • On certain pressure switches, hysteresis can be adjustable. On the basis of the control set up on the training system, the trainee is to get to know the hysteresis of a piston-type pressure switch. With the help of a 24 V bulb, which serves as control unit, and a pressure relief valve installed in a by-pass, he/she can set given values and measure the hysteresis by way of the hydraulic pressure. Notes on detailed technical information about the piston-type pressure switch: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 15 • Technical data sheet RE 50060 Hydro-electrical pressure switch

16



Project definition

Scatter min.

Switching pressure differential in bar →

Pressure stage 100 bar

max.

As described in Project 15 a customer uses a piston-type pressure switch in hydraulic pressing equipment. For his technical documentation the customer requires detailed information about the hysteresis of this piston-type pressure switch. In addition, he wants to know, whether this is always the same, and if so, whether he can utilize this for the sequence of his control.

Lower switching pressure in bar →

Fig. 16.1 Practical example: Piston-type pressure switch

16

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a piston-type pressure switch (specialist qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing the customer order using, among others, technical data sheet RE 50060.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Working out the hysteresis of a piston-type pressure switch at various, given system pressures.

• Checking:


• Evaluating:


Notes

16




Item 1.1

Item 1.2

Item 0.1 Item 1.0

Measuring glass

Power unit limit

16

Fig. 16.2 Hydraulic circuit diagram: Pressure switch hysteresis




16 Note: The pressure switch is supplied with voltage via push-button S1.





Qty


Type designation

1.0

1


DD 1.1

1.2

1


DF 1.2

1.1

1


0.1

1


DZ 1.4

2


DZ 25

Hose

VSK 1

Symbol

DD 6E.1


16



Connection block

Measuring glass


D




Notes

16




Warning

Caution






Warning

Caution



2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set piston-type pressure switch Item 1.1 to 30 bar; to this end, set pressure relief valve Item 1.0 to 30 bar. To this end, close throttle Item 1.2 and operate push-button S1. 4. Set the system pressure to 25 bar on pressure relief valve Item 1.0.

16



Slowly increase the system pressure to 30 bar while observing indicator lamp H1 on the electrical control.

When the pressure rises to 30 bar, lamp H1 goes on.

Increase the system pressure by further 5 bar to 35 bar. During this, lamp H1 must not go out.

5. Slowly reduce the system pressure until lamp H1 goes out. The pressure indicated by the pressure gauge should be 27.5 bar.

This switching difference is called hysteresis.

Note: The value given under point 5 can deviate by 1 - 2 bar.

Caution


Evaluating the work results with regard to the customer requirement • A piston-type pressure switch always features hysteresis. • The pressure switch responds at increasing and falling pressure. •

On a piston-type pressure switch, hysteresis is not adjustable.

16


10


Notes

16

Project 17: Hydraulic accumulator


Project 17: Hydraulic accumulator Project/trainer information If, in a hydraulic control, a cylinder should be operable also in the event of a failure, for example of the hydraulic pump, the energy required for this can be taken from a hydraulic accumulator. Depending on their design, hydraulic accumulators are classified as: Piston-type, bladder-type and diaphragm-type accumulators. A hydraulic accumulator is a pressure vessel with a separating element, in which energy is stored. Hydraulic accumulators are used for storing energy, for damping, for leakage oil compensation, for holding pressures constant and for vehicle suspension. Safety notes (Excerpt from currently valid safety regulations - not exhaustive). Hydraulic accumulators are pressure vessels and are subject to national regulations valid at the place of installation. In Germany, these are the health and safety at work regulations (BetrSichV). The rating, manufacture and testing must comply with AD sheets. The installation, equipment and operation are regulated by "Technischen Regeln Druckbehälter“ (TRB) (technical rules for pressure vessels).

Warning

Caution

Welding, soldering or carrying out mechanical work on pressure equipment is prohibited. Pressure equipment must not be charged with oxygen or air. Pressure equipment (accumulators) must not be opened before the gas and fluid sides were depressurized. Accumulators contain nitrogen (risk of suffocation). Accumulators may only be protected by pressure relief valves, which comply with Directive 97/23/EC. Pressure accumulators may only be installed, repaired and put into service by specialist personnel trained in the field of hydraulics.

The following Project 17 is intended to impart knowledge of the possible applications of a diaphragm-type accumulator as energy storage. You could also explain how to check the gas pre-charge pressure. In the project order the trainee is to understand the behavior of a hydraulic cylinder in the event of a hydraulic pump failure and the withdrawal of energy from a diaphragm-type accumulator in a practical experiment set-up on the training system. Through this project task, the following knowledge is to be acquired: • Due to the compressibility of the filled-in gas, a diaphragm-type accumulator can be used for storing energy. • The oil volume that can be stored in the hydraulic accumulator depends on the size of the accumulator, the nitrogen pre-charge pressure and the system pressure. • The amount of oil available for withdrawal depends on the accumulator size, the nitrogen pre-charge pressure and the pressure difference between the minimum and maximum working pressure. • If the system pressure falls below the nitrogen pre-charge pressure, the hydraulic accumulator is completely discharged. On the basis of the control set up on the training system the trainee is to work out the possible application of a hydraulic accumulator as energy storage. The usable oil volume can be calculated on the basis of a hydraulic cylinder that is controlled by a 4/3 directional valve at different system pressures.

17



Notes on detailed technical information about the hydraulic accumulator: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components, Chapter 9 • Technical data sheet RE 50130 Accumulator safety valve • Technical data sheet RE 50150 Diaphragm-type accumulator

Project definition In a fixture, a tool is to be moved by means of a hydraulic cylinder into and out of the machining area. In the event of a hydraulic pump failure, the tool most be extended by means of stored energy. Since the customer has never utilized an accumulator before, he would like to know whether he selected the correct accumulator size, i.e. whether the usable accumulator volume is sufficient. He uses various system pressures and therefore requires documents that describe the usable volume. In addition, he is interested in test documents such as a table that shows the various system pressures and the usable oil volume.

17

Fig. 17.1 Practical example: Bladder and diaphragm-type accumulators with accumulator safety block



Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of a hydraulic accumulator (specialist qualification) • Handling of hydraulic components in line with functional needs



• Planning:

Planning and organizing the customer order by, among others, working out the topic of hydraulic accumulators (The Hydraulic Trainer - Basic Principles) and the technical data sheet RE 50130/Accumulator safety block.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system and calculation of the usable oil volume at different, given system pressures, and of the precharge pressure.

• Checking:


• Evaluating:


17




Item 0.2 Item 1.0 Item 1.4 Lead- sealed

Item 1.1

Item 0.1

Item 1.3 Item 1.2

Measuring glass

Power unit limit

17

Fig. 17.2 Hydraulic circuit diagram: Hydraulic accumulator




Circulation




17




Qty

1.0

1


1.1

1


DW 13E

1.2

1


DD 1.1

1.3

1


DS 2.1

1.4

1

Accumulator safety block for diaphragm-type accumulator

DZ 3.2

3


DZ 4.1

2


DZ 1.4

1

hose with quick release coupling with check valve

DZ 25

Hose

VSK 1

0.1 - 0.2



Type designation

Symbol

ZY 1.3

17



Connection block

Measuring glass


D




Notes

17




Warning

Caution




Warning

For connections, to which pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25. Hand-tighten the pressure gauge measuring lines at the relevant minimess connection of the hydraulic hose. The correct and proper fit of the component connections with hoses can be checked by slightly turning the hoses.

Warning

Caution

Observe direction of installation of check valve Item 1.3. Hand lever (P) on the accumulator safety valve open, rotary knob (T) of the discharge valve closed.




17


Task 1


Check the nitrogen pre-charge pressure: 3. Set the system pressure to 40 bar on pressure relief valve Item 1.2. The system pressure can also be read off from pressure gauge M2. Close the shut-off valve (hand lever P) of accumulator safety valve Item 1.4. The system pressure is now isolated in the accumulator.

Task 2

Switch the hydraulic pump off. Carefully open the discharge valve (rotary knob T) on the accumulator safety valve until the pressure shown on M2 slowly falls. The pressure slowly decompresses down to the gas charging pressure and then rapidly falls to 0 bar. The pressure value at which the pressure starts to fall quickly is the nitrogen charging pressure.

Usable accumulator oil volume: 4. Switch the hydraulic pump on again. Open the hand lever (P) on the accumulator safety block, close the discharge valve by means of the rotary knob (T).

Set the system pressure on pressure relief valve Item 1.2 to 10 bar. Extend and retract cylinder Item 1.0 by operating push-buttons S4 and S2 and provide markings on the base plate at the end positions (the stroke should be 200 mm). Retract cylinder Item 1.0 to the basic position.

5. Switch the hydraulic pump off.

Extend and retract cylinder Item 1.0 by operating push-buttons S4 and S2 until the piston does no longer move. The required oil volume is now taken from the hydraulic accumulator. Note the number of strokes (extending and retracting), including the residual stroke during extending and retracting, and enter the values in Table 17.2.

6. Switch the hydraulic pump on and set the system pressure on pressure relief valve Item 1.2 to 15 bar.

Repeat the experiment set-up as described under point 5 and enter the measurement results in Table 17.2. Repeat the experiment with the accumulator charging pressures given in Table 17.2.

Caution

After having completed practical work on the training system switch the hydraulic pump off! No pressure gauge may indicate a pressure! Unload the hydraulic accumulator via the accumulator safety valve (rotary knob T).

Evaluating Calculation of the useful volume of the accumulator On the basis of the total number of strokes of the hydraulic cylinder the useful volume of the hydraulic accumulator can be calculated according to the following formula. V =

d K2 • π 4

( a • s + x ) + (d

2 K

)

- d St2 •

(

π • e • s • z 4

V = useful volume of the hydraulic accumulator dK = bore of the hydraulic cylinder (25 mm) dSt = piston rod diameter of the hydraulic cylinder (16 mm) S = stroke length of the hydraulic cylinder (200 mm) a = number of complete extending strokes e = number of complete retracting strokes x = residual stroke of the extending hydraulic cylinder z = residual stroke of the retracting hydraulic cylinder

)

dm3   

17


10


Cylinder comes to a halt while extending

Cylinder comes to a halt while retracting z=s-y

Fig. 17.6 Residual stroke of the hydraulic cylinder

After having calculated the useful volume, prepare a characteristic curve (Diagram 17.1)

Measured values Hydraulic accumulator pre-charge pressue p0 = 10 bar Hydraulic No. of complete strokes accumulator Extending a Retracting e charging pressure M2 p in bar

Residual stroke in mm Retracting x

Extending z

Useful volume V in dm3

10

0

0

0

0

0

15

1

1

195

0

0.25

20

2

2

95

0

0.36

25

3

3

0

50

0.42

30

3

3

10

0

0.47

35

3

3

100

0

0.52

40

3

3

160

0

0.55

45

4

3

0

0

0.57

Table 17.2 Useful volume of hydraulic accumulator


17


11


0,6

Useful volume V in l

0,5 0,4 0,3 0,2 0,1 0 0

10

20 30 Charging pressure M2 p in bar

40

50

Diagram 17.1 re Table 17.2

Evaluating the work results with regard to the customer requirement • Due to the compressibility of the filled in gas, diaphragm-type accumulators can be used as energy storage. • The oil volume stored in the hydraulic accumulator depends on the accumulator size, the nitrogen pre-charge pressure and the system pressure. • The effective useful volume of the hydraulic accumulator depends on the accumulator size, the nitrogen pre-charge pressure and the pressure difference between minimum and maximum working pressure. • If the system pressure falls below the nitrogen pre-charge pressure, the hydraulic accumulator is completely unloaded. • The hydraulic accumulator is charged when the system pressure is higher than the nitrogen pre-charge pressure.

17


12


Notes

17

Project 18: Regenerative circuit


Project 18: Regenerative circuit Project/trainer information If in a hydraulic control the extension velocity of a hydraulic cylinder (area ratio 2 : 1) is to be doubled, a regenerative circuit (recovery of the returning oil) can be employed. In a regenerative circuit, the extending piston is pre-loaded. The working pressure is permanently applied to both areas (piston and annulus piston area) of the hydraulic cylinder when the piston is extending. The advantages of this control are the smaller pump displacement and the approximately identical extension and retraction velocity of the hydraulic cylinder. A disadvantages is the force loss during extending, because the force of the piston rod side counteracts the piston side. In the following Project 18 knowledge can be imparted of how to increase the velocity without enlarging the pump displacement. In the project order the trainee is to work out the behavior of a hydraulic cylinder, when the oil volume of the piston rod side is directly fed to the piston side during extending. On the basis of a practical experiment set-up on the training system, the trainee is to gain the following knowledge: • For a single-rod cylinder the area ratio can be calculated on the basis of the piston area and the annulus piston area. • In the case of a regenerative circuit, the volume of the piston rod side is directly fed to the piston side. • With a regenerative circuit, the required pump displacement can be reduced. With the help of the control set up on the training system the trainee is to get familiar with the typical behavior of a regenerative circuit. The hydraulic cylinder is controlled by a 4/2 directional valve. During extending, the oil volume of the piston rod side is directly fed to the piston side. The piston velocity is to be adjustable by means of a flow control valve. Notes on detailed technical information about the regenerative circuit: • Technical data sheet RE 48005/RE 48015 Velocity controls for on/off directional valves

18



Project definition On a machine tool the velocity of a feed cylinder is to be increased and thus the cycle time of the system shortened without changing the pump flow. The advance velocity (extending time of the hydraulic cylinder) is to be adjustable independently of the load. In order that the customer can understand the circuit structure of the control, he requires the associated documentation such as the hydraulic circuit diagram with parts list. He also requires a table of the travel times of the hydraulic cylinder with different flow control settings. Moreover, the customer wants to know which effect the increase in the cycle time has on the advance force.

Fig. 18.1 Practical example: Control block with hydraulic components such as directional, pressure and flow control valve

18

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet for velocity controls (specialist qualification) • Handling of hydraulic components in line with functional needs





• Planning:

Planning and organizing the customer order by, among others, working out the technical data sheets relating to velocity controls.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Preparation of a table of travel times and velocities and a comparison of pros and cons.

• Checking:


• Evaluating:


Notes

18




Item 0.2

Item 0.3

Item 1.1

Item 1.2

Item 0.1 Item 1.3

Measuring glass

Power unit limit

18

Fig. 18.2 Hydraulic circuit diagram: Regenerative circuit




Control 4/2 directional valve Extension -Single-rod cylinder-

18





Qty

1.0

1


1.1

1


1.2

1


1.3

1


DD 1.1

1


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

0.1 - 0.3


Type designation

Symbol

ZY 1

DW 3E

DF 3


18



Connection block

Measuring glass


D




Notes

18




Warning

Caution


Execution of the order Set up the control as described below: 1. Mount the components required according to parts list Table 18.1 in a clearly arranged form on the training system according to the prepared circuit diagram.


For connections, to which pressure gauges with minimess line DZ 1.4 are to be connected, use hydraulic hoses DZ 25.1. Hand-tighten the pressure gauge measuring lines at the relevant minimess connection of the hydraulic hose.


Warning

Caution





3. Set flow control valve Item 1.2 to scale position 1.0.

Extend hydraulic cylinder Item 1.0 by operating push-button S1. Measure the extension time; enter the extension time and pressures M3 and M2 at the end position of hydraulic cylinder Item 1.0 in Table 18.2.

18



Operate push-button S1, which causes the piston of hydraulic cylinder Item 1.0 to retract again; enter the retraction time of the piston and pressures M3 and M2 at the end position of hydraulic cylinder Item 1.0 in Table 18.2.

4. Set flow control valve Item 1.2 successively to scale positions 1.2, 1.4, 1.6, 1.8 and 2.0 and enter the individual measuring results in Table 18.2 as described under point 3. 5. Enter the calculated traversing velocities of the feed cylinder as characteristic curve in Diagram 18.1.

Caution

After having completed practical work on the training system, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Open the throttle check valve.

Scale position Cylinder piston Flow control valve

M2 p in bar

M3 p in bar

Travel time t in s

Velocity v in mm/s

1.0

Extended Retracted

50 0

50 50

19 28

10.5 7.1

1.2

Extended Retracted

50 0

50 50

16.5 20.7

12.1 9.7

1.4

Extended Retracted

50 0

50 50

11.6 14.7

17.2 13.6

1.6

Extended Retracted

50 0

50 50

8.6 10.5

23.3 19.0

1.8

Extended Retracted

50 0

50 50

6.8 8.4

29.4 23.8

2.0

Extended Retracted

50 0

50 50

5.3 6.5

37.7 30.8

Table 18.2 Measured values of regenerative circuit


6. Calculation of the area ratio of single rod cylinder ZY1 used in the regenerative circuit.

Required dimensions of the hydraulic cylinder: Piston diameter D Piston rod diameter d Solution: D2 • π = 4,9 cm2 4 D2 - d 2 • π A2 = = 2,9 cm2 4 4, 9 cm2 : 2,9 cm2 = 1,689 A1 =

(

)

Area ratio A1 : A2 = 1.69 : 1

= 2.5 cm = 1.6 cm

18


10


Cylinder in

Cylinder out

4 3,5

Velocity v in cm/s

3 2,5 2 1,5 1 0,5 0 0

0,5

1 1,5 Position of flow control valve DF3

2

2,5

Diagram 18.1 re Table 18.2

As mentioned in the introduction, a disadvantage of the regenerative circuit is that piston force FK counteracts annulus piston force FR, i.e. the remaining useful force is the force of piston rod area FST. For information, please find below notes on pressures and flows for a single-rod cylinder controlled in a regenerative circuit, including the required calculation formula.

Single-rod cylinder A special type of circuit for a single-rod cylinder is the regenerative circuit. In this circuit, the cylinder is extended when the directional valve takes the spool position … and the oil displaced from the piston rod chamber is fed together with the pump displacement to the piston chamber. Note: When neglecting the pressure drop in the lines and the directional valve, the pressure is identical on both sides of the cylinder. The cylinder force during extending consequently becomes Fext = p  AK – p  AR

18

Fext = p  ASt

= p  (AK – AR ) and the piston velocity with pump displacement qP Vext =

qP AK – AR

=

qP

AK

AR

ASt

ASt

because the pump flow must only fill the space that corresponds to the piston rod area.


11


For retracting of the cylinder with spool position … of the directional valve, the force is calculated as follows: Fretr = pB  AR – pA  AK the retraction velocity q Vretr = P AR Thus, it becomes obvious that with an area ratio of

ϕ=

AK =2 AR

the extension and retraction velocities become identical. Vext =

qP AK – AR

=

qP 2  AR – AR

qP

=

AR

= Vretr

The following is valid: Vext Vretr where

ϕ=

=

AK

AR consequently Vext Vretr Vext Vretr

=

=

qP  AR (AK – AR )  qP

=

AR AK – AR

→ AK = ϕ  AR AR

ϕ  AR – AR

=

AR AR  (ϕ – 1)

=

1 ϕ –1

1 ϕ –1

18


12


AK

AR

ASt F1 (out) F2 (back)

∆pmin

pA

qB

qA

qtotal = qB + qP

qA qP

Evaluating the work results with regard to the customer requirement • The area ratio of a single-rod cylinder can be calculated on the basis of the piston area and the annulus piston area. • In a regenerative circuit, the volume displaced on the piston rod side while the piston is extending is fed to the piston side. • In a regenerative circuit, the required pump displacement can be reduced.

18

Project 19: Rapid speed / creep speed control


Project 19: Rapid speed/creep speed control Project/trainer information A rapid speed/creep speed control can be used in a hydraulic circuit to control the advance velocity of a hydraulic cylinder independently of the load. In the following Project 19 you can impart knowledge of a velocity control. Here, a flow control valve is cut in and out on the piston rod side of the extending hydraulic cylinder. With this velocity control, pressure intensification occurs on the piston rod side. In the project order the trainee is to work out the behavior of a hydraulic cylinder when a flow control valve is activated by means of a directional valve while the cylinder is extending. On the basis of a practice-oriented experiment set-up on the training system the trainee is to gain the following knowledge: • With a rapid speed advance control the hydraulic cylinder extends at maximum velocity without any throttling. • The extension velocity can be varied independently of the load by means of an electrical limit switch by cutting in a flow control valve. • The return stroke of the hydraulic cylinder is performed at maximum velocity. • Pressure intensification occurs when a flow control valve is activated on the piston rod side. On basis of the control set up on the training system the trainee is to understand the typical behavior of a single-rod cylinder in such a rapid speed advance control. A 4/2 directional valve is used to control a hydraulic cylinder. With an additional 4/2 directional valve the oil volume of the piston rod side is fed via a flow control valve to the tank. The return stroke is performed at the maximum velocity possible. Notes on detailed technical information on the rapid speed advance circuit: • Technical data sheet RE 48005 Velocity controls for on/off directional valves

19



Project definition At the end of a production line, workpieces are to be lifted from a conveyor belt and put down on a pallet. The lifting movement is to be performed using a hydraulic cylinder. To achieve shorter cycle times, fast motion sequences are required. Due to changing workpiece weights, the residual stroke is to be performed independently of loads at strongly reduced velocity. The return stroke is to be performed as fast as possible. For his documentation, the customer wishes to obtain a travel/time diagram in addition to a hydraulic circuit diagram and a parts list.

Fig. 19.1 Practical example: Production line

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of velocity controls (specialist qualification) • Handling of hydraulic components in line with functional needs

19





• Planning:

Planning and organizing the customer order, by, among others, examining the technical data sheet for velocity controls.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system and preparation of a travel/time diagram.

• Checking:


• Evaluating:


Notes

19




Item 0.2

Item 1.0

Item 0.3

Item 1.4 Item 1.2

Item 1.1

Item 0.1 Item 1.3

Measuring glass

Power unit limit

19

Fig. 19.2 Hydraulic circuit diagram: Rapid speed advance circuit




red

red black

blue

black blue


Extension Rapid speed -Hydraulic cylinder-

Note on sensor B1/B2 Blue – red – black = plug colors


19




Qty

1.0

1


ZY 1.3

1.1 - 1.2

2


DW 3E

1.3

1


DD 1.1

1

2-flow control valve, adjustable, for one direction of flow, largely independent of viscostiy and pressure differential, with by-pass check valve

DF 3

2


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

1.4

0.1 - 0.3


Type designation

Symbol

red

B1/B2

2

Limit switch, inductive

black

DE 2 blue


19



Connection block

Measuring glass


D




Notes

19




Warning

Caution


Execution of the order Set up the controls as described in the following: 1. Mount the components required according to parts list Table 19.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution



Position limit switches B1 and B2 so that the change-over takes place in the middle of the total stroke.



19



3. Set flow control valve Item 1.4 to scale positio. 1.0.

Extend hydraulic cylinder Item 1.0 by actuating push-button S2. 4/2 directional valve Item 1.2 is operated by limit switch B1 and the flow is fed to the tank via flow control valve Item 1.4. When limit switch B2 is reached, 4/2 directional valves Items 1.1 and 1.2 are switched again to the rest position and the cylinder retracts. Enter the retraction time of the piston and the pressures M3 and M2 in Table 19.2. Enter the extension time over the entire stroke and pressures M2 and M3 (during operation at reduced velocity) in Table 19.2.

Release push-button S2. This causes the piston of hydraulic cylinder Item 1.0 to retract again. Enter the retraction time of the piston and pressures M3 and M2 in Table 19.2.

4. Set flow control valve Item 1.4 to scale position 1.5 and enter the measuring results in Table 19.2 as described under point 3.

Caution

After having completed the practical work on the training system, switch the pump off! No pressure gauge may indicate a pressure! Open the throttle check valve.

Measured values Flow control valve scale position

Hydraulic cylinder

Rapid speed

Advance

Return stroke

1.0

1.5

M3

p

bar

7

6

M2

p

bar

9

9

Time

t

s

<1

<1

M3

p

bar

50

50

M2

p

bar

80

80

Time

t

s

23

12

M3

p

bar

19

19

M2

p

bar

38

38

Time

t

s

<1

<1

Table 19.2 Measured values from the project order


19


10


For information, please find below the graphical representation of the piston velocity of the single-rod cylinder. Table 19.3 shows a function sequence chart commonly used in practice. Travel

y

x

Rapid speed

Advance

t Time

Return stroke

Diagram 19.1 Travel/time diagram

Item 1.1

Item 1.2

→ → Rapid speed lifting

1

0

→ Advance lifting

1

1

← ← Lowering

0

0

Table 19.3 Function chart

Legend:

0 not operated 1 operated

Evaluating the work results with regard to the customer requirement • With a rapid speed advance circuit, the piston of a hydraulic cylinder extends with maximum pump flow without throttling. • With the help of an electrical limit switch, the extension velocity can be adjusted - controlled by a directional valve - independently of the load by means of a flow control valve. • The return stroke of the piston is performed with the maximum pump flow. • When the flow is throttled at the piston rod side, pressure intensification occurs during extending.

19

Project 20: Valve circulation control


Project 20: Valve circulation control Project/trainer information A circulation control for a fixed displacement pump can be used to prevent the hydraulic fluid from excessive overheating. Overheating would not only lead to premature wear of the hydraulic fluid, but can also result in lubrication problems. If the hydraulic pump displaces hydraulic fluid via the pressure relief valve while the hydraulic cylinder is at a standstill, more energy is consumed. In the following Project 20 you can impart knowledge of a valve circulation control. In the project order the trainee is to work out the possibility of directing the pump flow via a circulation valve. In a practice-oriented experiment set-up on the training system, the following knowledge is to be gained through the project task: • When the pump flow circulates, only a small pressure builds up in the hydraulic pump. • The circulation control reduces wear of the hydraulic pump. • Circulation helps to save electric power. • When the hydraulic fluid circulates, the fluid is not excessively heated and its service life extended. Based on the control set up on the training system the trainee is to implement a circuit for circulating the pump displacement. A hydraulic cylinder is to be controlled by means of a 4/3 directional valve with circulation position. When no hydraulic energy is required, the directional valve is brought to the central position, i.e. to the circulation position. In a further control circuit, the hydraulic cylinder is to be controlled by means of a 4/3 directional valve with blocked central position. However, in this case, the system pressure can only build up, if the flow previously discharged via a 4/2 directional valve is directed to the 4/3 directional valve. Notes on detailed technical information about the pump control: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components • Technical data sheet RE 10089 Fixed displacement pump/external gear pump

20



Project definition For the assembly of heavy hydraulic control blocks, a scissors lift it used for lifting and lowering pallets. In order that the hydraulic cylinder can be stopped at any position, a 4/3 directional valve with blocked central position is used. To spare the hydraulic pump, a solution is to be provided, with which the pump flow is directed at zero pressure to the tank when the hydraulic cylinder is not operated. The customer wishes to obtain several solution proposals and for his documentation, apart from the hydraulic circuit diagram and the parts list, a comparison of the proposed solutions.

Fig. 20.1 Practical example: Scissors lift

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the technical data sheet of fixed displacement pump (specialist qualification) • Handling of hydraulic components in line with functional needs

20





• Planning:

Planning and organizing the customer order, among others, through dealing with the technical data sheet for the 4/3 directional valve, RE 23178, and in particular with the section of symbols.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Acquisition of measured values and preparation of a comparison table.

• Checking:


• Evaluating:


Notes

20




Item 0.2

Item 0.3

Item 1.1

Item 0.1

Item 1.4

Measuring glass

Power unit limit

20 Fig. 20.2 Hydraulic circuit diagram: Pressureless circulation using a 4/3 directional valve




Circulation


Extension Retraction -Single-rod cylinder-

20 Fig. 20.3 Wiring diagram for hdraulic circuit diagram Fig. 20.2




Item 0.2

Item 0.3

Item 1.1

Item 1.3

Item 0.1

Item 1.4

Measuring glass

Power unit limit

20 Fig. 20.4 Hydraulic circuit diagram: Pressureless circulation using an additional 4/2 directional valve




Circulation

Control 4/3 directional valve - 4/2 directional valve Retraction

Extension Circulation

-Single-rod cylinder-

20 Fig. 20.5 Wiring diagram for hydraulic circuit diagram Fig. 20.4




Qty

1.0

1


ZY 1.3

1


DW 4E

1.2

1


DW 13E

1.3

1


DW 3E

1.4

1


DD 1.1

1


DZ 4.1

3


DZ 1.4

3


DZ 25

Hose

VSK 1

1.1

0.1 - 0.3


Type designation

Symbol

Table 20.1 Parts list for hydraulic circuit diagram Fig. 20.2 and 20.4

20



Connection block

Measuring glass


D




Notes

20


10


Connection block

Measuring glass


D




Notes

20


11



Warning

Caution


Execution of the order Set up the controls as described in the following: 1. Mount the components required according to parts list Table 20.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution


To make clear that in the central position the total amount of fluid flows through 4/3 directional valve Item 1.1, port T of directional valve Item 1.1 can be connected to the measuring glass (option).


2. Switch the hydraulic pump on and inspect the set up control for leakage. No pressure gauge may indicate a pressure. 3. Set the system pressure on pressure relief valve Item 1.4 to 50 bar plus one turn.

The system pressure can only be adjusted while the cylinder is at its end position.

20


Task 1

12


Flow in central position 4. Hydraulic cylinder Item 1.0 can be traversed with the help of push-buttons S2 and S4 as described in the project task.

Note pressure M1 in the relevant end position of hydraulic cylinder Item 1.0 while directional valve Item 1.1 is in its central position. Before making any conversion for further order processing, switch the hydraulic pump off! No pressure gauge may indicate a pressure! Caution

Task 2

Circulation 5. Mount the components required according to parts list Table 20.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution


To provide more clarity that the entire flow is fed directly to the tank via 4/2 directional valve Item 1.3 when directional valves Item 1.2 and Item 1.3 are not operated, port T of directional valve Item 1.3 can be connected directly to the measuring glass (option).




The system pressure can only be adjusted while the cylinder is at its end position.

7. Hydraulic cylinder Item 1.0 can be controlled via directional valve Item 1.2 using push-buttons S2 and S4. To this end, directional valve Item 1.3 must be operated before by means of push-button S3.

Measure and note pressure M1 in the relevant end position of hydraulic cylinder Item 1.0 (S2, S4 operated) while directional valve Item 1.3 is not operated.

Caution

After having completed the practical work on the training system, switch the pump off! No pressure gauge may indicate a pressure! Open the throttle check valve.

20


13


Measured values Task 1

M1 p in bar Circulation

Task 2 p in bar

p in bar

0

8

0

8

a

50

a

50

b

50

b

50

Cylinder end position

Table 20.2 Actual pressure values with different valve settings


Evaluating the work results with regard to the customer requirement • When the pump displacement is circulated, only a small pressure builds up in the hydraulic pump. • The circulation circuit reduces wear of the hydraulic pump. • Circulation saves electric power. • Due to the circulation circuit, hydraulic fluid does not heat up excessively, and the service life of the fluid is extended.

20


14


Notes

20

Project 21: Commissioning, troubleshooting, maintenance


Project 21: Commissioning, inspection, maintenance, troubleshooting, repair Project/trainer information A long service life and functional reliability of hydraulic systems and their components depend on proper handling. The observation of system-specific installation and operating notes of the supplier guarantee trouble-free operation. Important information can also be found in the technical data sheets for components, power units, and their accessories. Not only for the engineering, but also for everyday handling of modern hydraulic systems, regulations and safety rules must be observed. The main task of responsible persons (fitters, but also operators) is to keep systems in operation. A precondition for meeting this requirement cost-efficiently is profound knowledge. The persons involved must be able to read and interpret not only hydraulic circuit diagrams, but also electrical circuit diagrams. Troubleshooting in modern controls requires the skillful handling of measuring and diagnosis devices such as pressure gauges, multi-meters, flowmeters, etc. Repair and servicing staff must consider the entire system in examinations. Here, condition monitoring and the determination of machine operating schedules form the basis for active maintenance. According to DIN 31051 maintenance includes the sum of all measures for maintaining and restoring technical systems. Repairs are measures for restoring the desired condition of a system. Commissioning is the provision of an operable system. Maintenance includes measures for maintaining the desired condition of a system. Inspection is an assessment of the actual condition of a system. Repairs, commissioning, maintenance, and inspections may only be carried out by trained and instructed personnel having a specific knowledge of hydraulics. A specialist is, who, due to his/her technical training and experience, has sufficient knowledge and is sufficiently familiar with relevant regulations that he/she: • can assess the work assigned to him/her, • can recognize possible hazards, • can take the necessary measures to eliminate risks, • has the required knowledge with regard to repairs and assembly. Environmental protection also plays an important role, especially for maintenance personnel. For example, oil-soaked cloths and paper must be properly disposed of. In the project order the trainee is to work out commissioning of a hydraulic control and the procedure for component adjustments. On the basis of a practice-oriented experiment set-up, the following knowledge is to be gained in the course of the project task: • For commissioning, system-related machine documents such as circuit diagrams, parts list, function charts, system parameters and operating instructions are required. • Contamination is by far the most common cause of faults in hydraulic systems. • Improper mounting can significantly reduce the service life of hydraulic components and leads to costly downtimes.

21



• An indispensable tool for targeted fault analyses is the understanding of the function and operating principle of all hydraulic components in the system. • Target-oriented communication simplifies the analysis of faults. • Preventive maintenance and inspection reduce failures of systems and prolong the service life of components. On the basis of the complex control set up on the training stand, the trainee is to work out commissioning of an electrohydraulic control and the order of adjusting the individual components. Controlled by a 4/3 directional valve, a hydraulic cylinder is to lift a load. The lifting time is to be adjusted by means of a throttle and take approx. 5 s. A hydraulic motor (set to 1.5 l/min), which is to rotate independently of the load by using a flow control valve, is hydraulically pre-loaded by a 4/2 directional valve connected in parallel. Controlled by an electrical push-button, first the cylinder is to lift the load, and then the hydraulic motor is to rotate uniformly. Notes on detailed technical information about the project order: • The Hydraulic Trainer Volume 1/Bosch Rexroth AG Basic principles and components • Technical data sheets for all hydraulic components listed such as directional, pressure, and flow control valves • Technical data sheet RE 07100-B Hydraulic cylinders/operating instructions (exemplarily for notes on: commissioning, inspection, maintenance, repair) • General product information on hydraulic products Technical data sheet RE 07008

21



Project definition On a machine tool, a workpiece is to be machined by a tool, which is powered by a hydraulic motor. Before being machined, the workpiece is to be lifted by a lifting cylinder to the machining position. The customer wishes to obtain the required machine documents such as hydraulic and electrical circuit diagrams with parts lists, system parameters and commissioning instructions such as the order of adjustment of hydraulic components for documentation purposes. To be able to advise the electrician, which solenoids are to be switched for the individual process sequences, he requires a simple diagram showing the function sequence. In addition, he wishes to obtain notes on preventive maintenance and inspection. A flow chart is to provide information about assumed faults (hydraulic motor does not rotate).

Fig. 21.1 Practical example: Machine tool control (not project-related) Principle structure of a complex machine tool with components covering all technologies

Project tasks • Independent understanding of the task and its putting into practice using hydraulic control technology • Planning and organizing the customer requirement (core qualification) • Analyzing the required technical documents (specialist qualification) • Handling of hydraulic components in line with functional needs

21





• Planning:

Planning and organizing the customer order, among others, by dealing intensively with technical data sheets.

• Deciding:


• Executing:

Set-up of the hydraulic control on the training system. Acquisition of measured values and preparation of the technical documentation requested by the customer.

• Checking:


• Evaluating:


Notes

21



Notes

21



Hydraulic circuit diagram Item 1.0 Item 0.4 Item 2.0

Item 0.2

Item 0.3 Item 2.2

Item 2.3 Set to 1.5 l/min

Item 1.3 Item 1.1

Set to text = 5 sec

Item 2.1

Item 0.1 Item 1.2

Measuring glass

Power unit limit

Fig. 21.2 Hydraulic circuit diagram: Machine tool control

21




Stop

Control 4/3 directional valve - 4/2 directional valve Extension Retraction Lifting Lowering

Fig. 21.3 Wiring diagram for the machine control

-Single-rod cylinder-

Rotation -Hydraulic motor-

21




Qty


1.0

1

Double-acting cylinder with singlesided piston rod with load

1.1

1


DW 13E

1.2/2.3

2


DD 1.1

1.3

1


DF 1.2

2.0

3

Fixed displacement motor with external leakage oil line and two directions of rotation

DM 8N

2.1

1


DW 3E

3


DF 3

3


DZ 4.1

4


DZ 1.4

4


DZ 25.1

2.2

0.1 - 0.4

hose Table 21.1 Parts list for hydraulic circuit diagram Fig. 21.2

Type designation

VSK 1

Symbol

21



Connection block

Measuring glass


D




21


10



Warning

Caution


Execution of the order Set up the control as described below: 1. Mount the components required according to parts list Table 21.1 in a clearly arranged form on the training system according to the prepared circuit diagram.




Warning

Caution





21


11


Commissioning: Lifting cylinder 3. Activate 4/3 directional valve Item 1.1 by means of electrical push-buttons S2 (extending/lifting) and S4 (retracting/lowering) to traverse hydraulic cylinder Item 1.0. The lifting velocity of approx. 5 s is set on throttle valve Item 1.3.

Measure pressure M1, M2 and M3 during operation of the lifting cylinder and enter the values in system parameter sheet Table 21.2.

Commissioning: Hydraulic motor 4. Upon the activation of 4/2 directional valve Item 2.1 by means of electrical push-button S3 hydraulic motor Item 2.0 rotates clockwise.

While the hydraulic motor is rotating, adjust flow control valve Item 2.2 so that a flow of approx. 1.5 l/min can be measured by means of the measuring glass. After having adjusted the speed of the hydraulic motor while the latter was rotating, set pressure relief valve Item 2.3 to a hydraulic pre-load pressure of 20 bar.

Acquire pressures M1 and M4 while the hydraulic motor is rotating and enter the values in system parameter sheet Table 21.2. For system-inherent reasons, the motor only rotates clockwise!

Caution


Measured values Actuator

Lifting cylinder

Lifting cylinder

Hydraulic motor

Function

Lifting

Lowering

Rotating

Measuring point

Value in bar

M1

48

M2

0

M3

5

M1

48

M2

47

M3

30

M1

48

M4

20

Table 21.2 System parameters of machine tool control


21


12


For a simple representation of the function sequence of an electrohydraulic control, function charts as shown below are used in practice. Travel/increment or travel/time diagrams can be used additionally for representing movements of more complex controls.

Valve solenoid

Lifting cylinder

Hydraulic motor

Y1.a

Y1.b

Y2

Lifting

1

0

0

Lowering

0

1

0

Holding

0

0

0

Rotating

0

0

1

Stop

0

0

0

Table 21.3 Function sequence/machine tool control

Legend:

1 Valve spool energized 0 Valve spool not energized

21


13


Machine tool control Example of fault: Hydraulic motor/machining motor does not rotate Process sequence

• The machine operator loads the workpieces at a defined position. • The machine operator closes the door to the working range of the machine tool, with a check made by sensors to guarantee compliance with safety regulations. • After the workpiece position was checked, the operator actuates push-button S2 to lift the workpiece by means of lifting cylinder Item 1.0 to the machining position (on sight). Lifting time text in 5 s. • Machining of the workpiece is accomplished with hydraulic motor Item 2.0 (rotating clockwise). To this end, the machine operator actuates push-button S3 (on sight).

Constant, load-independent rotating of the hydraulic motor by means of flow control valve Item 2.2 which is set to qV = 1.5 l/min and pre-loading valve Item 2.3 set to 20 bar.

• After completion of the machining process, the machine operator stops the hydraulic motor by actuating push-button S5 and then moves the workpiece to the basic position for the hydraulic cylinder by operating push-button S4. • Chips produced during machining are transported from the operating range of the machine tool by a chip conveyor.

Sequence chart for troubleshooting

Workpiece correctly put down? ↓ ↓

yes

no →→→

→→→

System pressure available?

Check loading

Are faults/fault messages present such as: filter, oil level, temperature? no →→→

Is the pump running?

no →→→

Check motor

no →→→

Check pump controller

→→→

Check by activating emergency stop

↓ yes ↓ ↓ ↓

Lifting cylinder Item 1.0 at end position? ↓ ↓

no →→→

Check and, if required, correct position

no →→→

Is the valve spool jammed?

no →→→

Check settings

yes Valve Y2 activated

↓ ↓

Pump pressure available?

yes

yes

yes

Flow control valve Item 2.2 open?

↓ yes ↓

Note: Possibly mechanical fault of the hydraulic motor? ↑ ↑

Load pressure too high?

yes →→→

Check DB valve Item 2.3/20 bar

21


14


Questions Question 1: Name the systematic working steps during commissioning and for adjusting the electrohydraulic control. • Check the electrical control for function • Check the set-up of the hydraulic control • Set the pressure relief valves to minimum pressure/spring unloaded • Adjust flow control valves to adequate flow • Switch the hydraulic pump on/Leakages?/Direction of motor rotation OK?/No excessive pressures in the system? • Set the system pressure to 50 bar plus one turn/DB valve Item 1.2 • Check the LIFTING/LOWERING function of the lifting cylinder/push-buttons S4 - S2 • Adjust the lifting time to 5 s/throttle Item 1.3 • Measure the operating pressures and enter them in the system parameter table • Check the rotating function of the hydraulic motor. • Adjust the rotary speed/close flow control valve/measure the flow by means of the measuring glass/1.5 l/min. • Set the pre-loading valve/DB valve Item 2.2 to 20 bar. • Enter the machining pressure of the hydraulic motor in the system parameter table Question 2: Which 6 machine documents are indispensable for electrohydraulic systems? • Hydraulic circuit diagram/with parts list • Wiring diagram • Function chart • Operating instructions • Machine key data/system parameters • Measurement report of initial commissioning Question 3: Why should a hydraulic system be flushed prior to initial commissioning? • The flushing process removes dirt particles from the individual components such as pipes. It must be ensured that the permissible maximum cleanliness class to ISO 4406 KL. 21/18/15 is not exceeded for the entire system. Question 4: How should the hydraulic fluid be disposed of? • The fluids must be disposed off in accordance with environmental regulations, i.e. the contaminated fluid must be made available to approved recycling companies in suitable containers for disposal. The notes on waste disposal given in the safety data sheet of the hydraulic fluid must be observed. Question 5: Into which areas is maintenance subdivided? • DIN 31051 classifies maintenance in the following areas: Maintenance - Inspection - Repair Question 6: Which work (measures) must be carried out during an inspection? • Check of set operating values • Visual inspection of the complete system for external leakage, wear, damage, ... • Check of hydraulic fluid for fluid level and appearance

21


15


Question 7: Which work (measures) are to be carried out during maintenance? • Changing the filter inserts • Checking or changing the hydraulic fluid • Cleaning the inside of the tank, if required • Replacing hydraulic hoses at given intervals Question 8: Which of the following faults are causes for malfunction that can be traced back to improper installation and which faults occur on running systems? • Incorrect directional valve installed • Electric motor incorrectly connected • Contaminated hydraulic fluid • Hydraulic hose improperly connected • Wear of hydraulic seals • Filter clogged • Cable break at the connection of the solenoid • Pressure switch does not switch • Hydraulic component does not operate due to a broken spring • Throttle bore clogged on the pilot part

Improper installation during initial commissioning: • Incorrect directional valve installed • Electric motor incorrectly connected • Hydraulic hose improperly connected • Pressure switch not set to the correct value

Faults on running systems: • Contaminated hydraulic fluid • Wear of seals • Filter clogged • Solenoid cable break • Limit switch does not switch, loose • Spring broken in hydraulic element, does not work • Throttle bore clogged

Question 9: Name a systematic order for the localization and elimination of faults. • Recognizing faults on the system and their effect • Analyzing the cause of fault • Planning of how to eliminate the fault • Proper elimination of the fault • Re-commissioning the system • Documenting the fault and its elimination

21


16


Evaluating the work results with regard to the customer requirement • For correct commissioning, system-related machine documents are required such as circuit diagrams, parts list, function charts, system parameters and operating instructions. • Contamination is the most common cause of faults in hydraulic systems. • Improper installation can shorten the service life of hydraulic components. • Preventive maintenance and repair reduce system failures and prolong the service life of components. • An important precondition for target-oriented troubleshooting is the knowledge of the function and the operating principle of all hydraulic components.

21


17


Notes

21

General product information on hydraulic products

DE EN FR IT FI ES NL SV PT DA EL

RE 07008/02.05

Ihre Sprache? – Siehe Rückseite! Your language? – See back page! Votre langue ? – Voir au dos ! La vostra lingua? – Vedi retro! Kohdekielet? – Katso takankatta! ¿Su idioma? – ¡Vea al dorso! Uw taal? – Zie achterzijde! Ditt sprak? – Se omslagets baksida! O seu idioma? – Consulte a contracapa! Dit sprog? – Se bagside! Η γλώσσα σα; – Βλέπε πίσω πλευρά!

1/32

2/32

Bosch Rexroth AG

Hydraulics

Contents 1

2

3

4

5

6

General product information

Page

Important basic information

4

1.1

Conventions used in this product information

4

1.2

What you need to know about this product information

4

1.3

The contents of this product information

4

Scope of delivery and responsibilities

5

2.1

Scope of delivery and responsibilities of Bosch Rexroth

5

2.2

Responsibilities of the plant operator

5

2.3

Liability, guarantee, warranty

6

2.4

Copyright

6

Important basic safety instructions

7

3.1

What to do in an emergency

7

3.2

Safety labelling on the hydraulic product

7

3.3

Proper use

7

3.4

Requirements for personnel, duty of care

8

3.5

General ancillary dangers and protective measures when operating hydraulic products

9

Technical data and ambient conditions

11

4.1

Information about pressure fluids

11

4.2

Ambient conditions

11

What you need to know about pressure fluids

13

5.1

How to handle pressure fluids safely

13

5.2

Functions and effectiveness

13

5.3

Viscosity

13

5.4

Leakage fluid

14

5.5

Topping up/refilling

14

Construction and mode of operation of a hydraulic system

15

6.1

Definitions of terms

15

6.2

Schematic

15

6.3

Safety concept

15

7

Moving hydraulic units/components

16

8

Storage and longer standstills

16

8.1

Hydraulic systems - subsequent bringing into use after storage

16

8.2

Seals, hoses and hose lines

17

RE 07008

RE 07008


Hydraulics

Bosch Rexroth AG

Contents 9

3/32

Page

Assembly and bringing into first use

18

9.1

Safety advice for assembly and bringing into first use

18

9.2

Before bringing into first use

18

9.3

Bringing into first use, subsequent bringing into use

19

10

Operation

22

11

Trouble-shooting

22

11.1

What to do in the event of a fault

22

11.2

The basic approach to trouble-shooting

22

11.3

Trouble-shooting tables

23

12

13

14

Maintenance

24

12.1


24

12.2

Safety during maintenance tasks

24

12.3

Inspection and servicing

25

12.4

Service and storage lives of hose lines

28

12.5

Topping up the pressure fluid

29

12.6

Servicing pressure accumulators

29

12.7

Repair

29

General information about hydraulic pressure accumulators

30

13.1

General

30

13.2

Safety devices relating to hydraulic pressure accumulators

30

Hydraulic systems

31

14.1

31

Effects of leaks in the hydraulic system on the machine

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1 1.1

Bosch Rexroth AG

Hydraulics

Important basic information Conventions used in this product information

Cross-references are printed in italics.

DANGER This symbol indicates a threat of danger which will result directly in death or very serious injury if not avoided.

WARNING This symbol indicates a threat of danger which may result in death or very serious injury if not avoided.

CAUTION This symbol indicates possible danger which may lead to minor or serious injury and/or to material damage.

IMPORTANT


Observing the product information and Operating Instructions Ø

reduces downtimes and maintenance costs

Ø

increases the service life of your hydraulic products.

The Operating Instructions must be directly accessible to one of the personnel at the hydraulic product and kept readily available at all times in a place known to the personnel. The Operating Instructions must be read and understood and all its provisions observed by those responsible and by the operative personnel. We recommend that a record is made in writing of the employees’ familiarisation with all the relevant parts. The cross-references to directives, standards and regulations contained in this product information refer to the versions current at the time of writing of this product information, which can be obtained from the title page of this product information.

1.3

What you need to know about this product information

This product information applies to the following types of hydraulic products: Ø

Hydraulic components

Ø

Hydraulic power units

Ø

Hydraulic systems.

The contents of this product information

In addition to this document, product information for Rexroth hydraulic products normally includes Operating Instructions consisting of three parts: Ø

Part I, the general Operating Instructions for the relevant class of products

Ø

Part II, the Technical Datasheet

Ø

Part III, the Product- and Application-specific Operating Instructions.

This symbol indicates additional information.

1.2

RE 07008

If you do not have all three parts, please request the missing part from Bosch Rexroth. Only if all the information contained in all parts of the three-part Operating Instructions is observed can safe operation of Rexroth hydraulic products be ensured. Specific cross-references are used to draw your attention to information that you can find in the Operating Instructions. The Operating Instructions contain detailed information about the product, including Ø

Information about the scope of delivery

Ø

Safety instructions

This product information applies exclusively to hydraulic products that are operated with mineral-oil-based pressure fluids, if the Operating Instructions do not expressly permit the use of other pressure fluids.

Ø

Technical data and operating limits

Ø

Information about bringing into (first) use and maintenance

Ø

Information about the mode of operation

IMPORTANT

Ø

Layouts, drawings

As this product information for Rexroth hydraulic products applies in a general sense, some of the content may not necessarily apply to the hydraulic product you have purchased.

Ø

Parts lists if appropriate

Ø

Information about replacement parts and accessories.

However, only by strictly observing this product information and the Operating Instructions can accidents be prevented and problem-free operation of your Rexroth hydraulic product be guaranteed.

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Hydraulics

Bosch Rexroth AG

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2

Scope of delivery and responsibilities

Installation of Rexroth hydraulic products in a machine or system may increase this value, and if so, the manufacturer of the machine/system must document this.

2.1

Scope of delivery and responsibilities of Bosch Rexroth

At or above 85 dB(A), the plant operator must make suitable hearing protection available to the personnel.

Rexroth hydraulic products fulfil all safety requirements applicable to fluid power systems and their components.

IMPORTANT For the scope of delivery and the responsibilities of Bosch Rexroth with respect to the product, please refer to the Product-specific Operating Instructions.

2.2

Responsibilities of the plant operator

CAUTION If Rexroth hydraulic products are positioned in the vicinity of sources of ignition or strong radiators of heat, protection must be put in place that would prevent any escaping pressure fluid from igniting and the hose lines from aging prematurely. Mineral-oil-based pressure fluid is hazardous to water and flammable. It may only be used if the relevant safety datasheet from the manufacturer is available and all the measures stipulated therein have been implemented. If there is a risk of fluid leaking from the hydraulic product and contaminating water or the ground, the hydraulic product in question must be placed in a suitable collecting trough. In connection with this, the applicable statutory regulations must be observed. You must also observe the EU directives for the use of work equipment (Directive 89/391/EC) and the associated individual directives, especially Directive 1999/92/EC for the protection from the danger arising from potentially explosive atmospheres and their implementations in national legislation. The legislation contains minimum requirements with respect to the making available by the employer of work equipment and for the use of work equipment by employees at work, including the regulations for operating equipment requiring supervision and the obligation to produce explosion protection documentation. This involves, for example, dividing areas endangered by potentially explosive atmospheres into zones and specifying suitable work equipment and procedures for these areas.

2.2.1 Noise protection The A-weighted equivalent continuous sound power level of Rexroth hydraulic products can be obtained from the relevant Operating Instructions. If no values are documented then it can be taken that the value is less than 70 dB(A).

2.2.2 Special points concerning the installation of certain products A Rexroth hydraulic product is intended above all for installation in machines, systems and power units as a part machine or a component for installation into another machine or system and is not a complete machine in the sense of the EU directive. In addition to the Machinery Directive, still further directives may apply, such as the Pressure Equipment Directive or the Explosion Protection Directive. A wide range of dangers can arise from the combined actions of the hydraulic product and the machine or system in which the hydraulic product is installed. Therefore you must always make sure that the hydraulic product is also suitable without restriction for the proposed application at the installation location. The interfaces with the overall machine and the operating conditions are also of the greatest importance. We recommend that the results of the hazard analysis (risk assessment) of the overall machine are taken into account in the design of the hydraulic product. The functioning of the hydraulic product is also influenced by the machine or system in which it is installed. For this reason, you must also always observe the Operating Instructions of the overall system in which your hydraulic product is installed. It is most important for you to also consider the possible use of the hydraulic product in a potentially explosive atmosphere (see 94/9/EC).

IMPORTANT Bosch Rexroth points out that, at the time of their first introduction on to the market, hydraulic products comply with the requirements of all relevant EU directives and/or their implementation into national legislation in Germany. If the scope of delivery is intended to be installed in a machine or system, then the Machinery Directive applies as appropriate – including the then currently applicable amendments – in that the scope of delivery does not necessarily comply with the requirements of the Machinery Directive because the scope of delivery is intended for installation in a machine or because the scope of delivery is intended for combination with other machines into a machine or a hydraulic system. The bringing into use of the scope of delivery shall therefore not be permitted until the machine or system in which the scope of delivery is to be installed or of which it represents a component complies with the requirements of all relevant EU directives. Details of further responsibilities can be found in 3 Important basic safety instructions and in the Operating Instructions.

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2.3

Bosch Rexroth AG

Hydraulics

Liability, guarantee, warranty

Bosch Rexroth shall not be liable for damages that result from non-compliance with or disregard of these and other parts of the Operating Instructions. Unauthorised tampering shall render the warranty null and void. Bosch Rexroth shall only be liable if the scope of delivery was shown to be defective. Bosch Rexroth shall not be liable if a deficiency occurs that involves parts having been replaced by the customer with equivalent but not identical parts as specified by the manufacturer. Please refer to our general terms of supply or your contract for details of the guarantee and manufacturer’s warranty.

2.4

Copyright

This product information may only be reproduced – electronically or mechanically, in whole or in part – with the express written permission of Bosch Rexroth. It may likewise not be distributed, amended, transmitted, translated into another language or employed or copied for other purposes or by other parties without such consent.


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3 3.1


Hydraulics

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Important basic safety instructions

IMPORTANT

What to do in an emergency

The hydraulic product shall be operated exclusively with pressure fluids complying with DIN 51524. Where other pressure fluids are permitted, for example brake fluids for brake valves, this is specially mentioned in the Operating Instructions.

In the event of an emergency, fault or other abnormal occurrences: 1.

Switch off the hydraulic system.

2.

Secure the main switch against being unintentionally switched on again.

3.

Secure the danger area so that no one can enter the danger area unknowingly or uncontrolled.

4.

Notify the relevant specialist personnel immediately.

5.

In the event of fire, observe the provisions of the safety datasheets issued by the manufacturer of the pressure fluid and the fire precautions specifically applicable to your place of work, which must be documented in the plant operator’s operating manual.

For details on proper use see 4 Technical data and ambient conditions. The following information can be found in the Operating Instructions: Ø

the proper use, specific to the hydraulic product

Ø

where applicable, the safety category in accordance with EN 954-1

Ø

non-permitted and improper use.

3.3.1 Proper use, requirements before operation Ø

WARNING Fighting fires with materials other than those permitted can lead to explosions and/or more rapid spread of the fire! Danger to life from smoke inhalation!

3.2

Bosch Rexroth AG

Safety labelling on the hydraulic product

Rexroth hydraulic products may only be operated if they are in perfect technical condition. •

In the event of disturbances in the power supply and/ or damage to the electrical equipment, switch off immediately and secure the main switch against being switched on again without authorisation.

•

Report and rectify all faults and damage indicated by the system or discovered by other means.

Ø

The connections, operating conditions and performance data specified in the Operating Instructions must be observed and never changed.

Ø

Rexroth hydraulic products shall not be converted or otherwise modified without prior consultation with Bosch Rexroth.

IMPORTANT Ø

The meanings of the safety labelling on the Rexroth product are explained in the Operating Instructions.

Ø

The plant operator shall not modify the program code of programmable control systems.

Ø

For a diagram of the nameplate and an explanation of the information on it please refer to the Operating Instructions.

Ø

Dependencies and time factors shall not be modified without prior consultation.

Ø

Rexroth hydraulic products are designed and constructed for the provision, transmission, control or regulation of energy and signals using the flow of oil.

The safety devices fitted by Rexroth must be present, properly installed and in full working order – except when this is impractical during setting up or maintenance work. They shall not be relocated, bypassed or rendered ineffective.

Ø

Unless otherwise agreed, the Rexroth hydraulic product satisfies at least safety category B in accordance with EN 954-1.

Safety components such as limit switches, valves and other control components shall not be rendered inoperative.

Ø

If the hazard analysis/risk assessment of the overall machine in which the Rexroth hydraulic product is to be installed indicates that a safety category higher than category B in accordance with EN 954-1 is required for the Rexroth hydraulic product, then a correspondingly higher rated hydraulic product can be supplied and installed only after special agreement with Bosch Rexroth.

Tamperproof lead seals installed by the manufacturer shall not be removed or damaged except when this is necessary in the course of maintenance tasks defined in the Operating Instructions.

Ø

The specified maintenance tasks in the Operating Instructions shall be carried out at the intervals stated in the Operating Instructions.

3.3

Proper use

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Ø

Ø

3.4

Bosch Rexroth AG

Hydraulics


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Uncontrolled access by persons unfamiliar with the system to the immediate operating zone of Rexroth hydraulic products is prohibited (even if the product in question has been shut down).

Servicing personnel (who carry out filter and oil changes, for example) shall fulfil the following requirements: Ø

They have been instructed in the relevant activity.

Rexroth hydraulic products must never be assembled, operated or maintained by persons under the influence of alcohol, drugs or other medication which affect one’s ability to react.

Ø

Specialist knowledge of hydraulics is not required to carry out servicing work.

Requirements for personnel, duty of care

3.4.1 Qualifications of specialist personnel A specialist person is someone who, using his specialist training, knowledge and experience as well as familiarity with the relevant conditions, can Ø

safely carry out the tasks allocated to him and correctly assess the scope and implications of his work

Ø

recognise possible dangers

Ø

undertake the necessary measures to eliminate possible accidents.

3.4.2 Requirements for hydraulics maintenance personnel In accordance with DIN 31051, maintenance comprises the individual activities of inspection, servicing and repair. All personnel involved in maintenance shall be familiar with and observe all parts of the Operating Instructions and this product information. Inspection personnel shall fulfil the following requirements:

Repair personnel shall fulfil the following requirements: Ø

The personnel must be hydraulics experts, who have been instructed and meet the definition given above,

Ø

Repair personnel must be familiar with the function of the hydraulic system as a whole, from subsystems to their interaction with the function of the entire machine.

Ø

Repair personnel must be able to read hydraulic circuit diagrams, interpret individual functions from their symbols and understand function diagrams.

Ø

Repair personnel must possess knowledge of the function and construction of hydraulic elements.

3.4.3 Requirements for electrical maintenance personnel All work on electrical equipment shall only be carried out by an authorised, qualified electrician, or by instructed persons under the guidance and supervision of a qualified electrician, in accordance with the rules applicable to electrotechnical products.

3.4.4 Minimum age Persons under the age of 18 who are currently receiving instruction or training or are working under supervision may not work on Rexroth hydraulic products.

Ø

They have been instructed in the relevant activity.

This does not apply to young persons of 16 or over if

Ø

Specialist knowledge of hydraulics is not required for purely inspection activities but the personnel must be aware of the particular dangers associated with hydraulic products.

Ø

working on Rexroth hydraulic products is necessary in order for them to accomplish a training objective

Ø

their protection is guaranteed by the supervision of an experienced, competent person

Ø

they are allowed to use only tools, work implements and protective gear that preclude the risk of injury.

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3.4.5 Training

Hydraulics

Observation and use of the Operating Instructions and legal requirements

Ø

Proper operation of the Rexroth hydraulic product

Ø

Observation of the instructions of safety officers and the plant operator’s operating manual

Ø

What to do in an emergency.

IMPORTANT Bosch Rexroth can provide you with training support in specialist areas.

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3.5.1 Dangers from pressure fluid

The plant operator using Bosch Rexroth hydraulic products shall train his personnel regularly in the following subjects: Ø

Bosch Rexroth AG

CAUTION Handling pressure fluid without protection is hazardous to health. Please observe the manufacturer’s safety instructions and the safety datasheets for the pressure fluid that you are using.

DANGER Serious damage to health or death may result if pressure fluid enters the blood stream or is swallowed. If this occurs, contact a doctor immediately!

An overview of the training can be found on the Internet at http://www.boschrexroth.de/didactic.

3.5.2 Malfunctions due to contamination of pressure fluid

3.5

General ancillary dangers and protective measures when operating hydraulic products

Contamination of the pressure fluid can be caused by: Ø

Wear during operation of the machine/system (metallic and non-metallic abrasion)

Ø

Leaks of the hydraulic product

Ø

Contaminants introduced during servicing/repair

In the interests of your safety, all safety instructions shall be carefully observed, especially those in the Operating Instructions.

Ø

The use of dirty (unfiltered) pressure fluid when the pressure fluid is changed.

In spite of the high intrinsic safety of Rexroth hydraulic products, the risk of personal injury or damage to the environment cannot be excluded, even when the equipment is properly used.

Contaminants lead to malfunctions, increased wear and shorter service life of the hydraulic product. This can have negative effects on the safety and reliability of the hydraulic product.

DANGER

New, additional dangers may arise if the hydraulic product is installed in another machine or installed with other machines in a system. This shall apply in particular to mechanical movements generated by the hydraulic product. Information on these additional dangers can be found in the overall operating manual of the supplier of the overall system in which the hydraulic product is installed.

Therefore the maintenance tasks specified in the Operating Instructions shall be carried out at regular intervals and the utmost cleanliness is required during work on the hydraulic product.

CAUTION When changing the pressure fluid, always use factory-fresh pressure fluid and filter it before filling to remove any contaminants in the pressure fluid that it often contains from the packaging container (drum). Flush out lines and hoses before installation. The cleanliness class of a pressure fluid is specified in accordance with ISO 4406. Detailed information can be obtained from the relevant datasheet or the Operating Instructions.

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Bosch Rexroth AG

Hydraulics

In older datasheets, the cleanliness class is sometimes specified in accordance with NAS 1638. The following table can be used to convert this to an equivalent ISO 4406 cleanliness class: Comparison table for cleanliness classes Earlier class to Current class to NAS 1638 ISO 4406 (c) Class 7 Class 18/16/13 Class 9 Class 20/18/15

3.5.3 Electrical dangers


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3.5.4 Product-specific ancillary dangers All product-specific ancillary dangers and precautions can be found in the relevant Operating Instructions.

3.5.5 Disposal Ø

Take metal, cable and plastic ducts to a recycling materials collection centre.

Ø

Dispose of electronic components as electronic waste.

Ø

Dispose of back-up batteries as special waste.

Ø

Cleaning agents, operating fluids and other materials:

When working on electrical systems: •

De-energise the hydraulic system before beginning any maintenance work.

•

Cordon off the working area with red-white safety chain and warning signs.

•

Lock the main switch, remove the key and keep it in a safe place until the work is completed.

•

Attach a warning sign to the main switch.

•

Check that there is no voltage using a two-pole voltage detector.

•

Earth and short-circuit the point where you are working.

•

Cover neighbouring live parts.

•

Clear your workplace to prevent contact with live parts as a result of tripping or slipping. Wear safety footwear.

•

Always use electrically insulated tools.

•

Disconnect plugs at sensors and valves – even those with low voltages – after the system has been de-energised.

DANGER Even after disconnection of the electrical supply (main switch OFF) the following supply systems/danger areas can still give rise to life-threatening voltages: Ø

Electrics, electronics, hydraulics (e.g. accumulators, rechargeable batteries)

Ø

Main switch

Ø

Power supply cables

Ø

Points identified with an electric shock warning sign.

CAUTION Please observe the disposal regulations specified in the appropriate Safety Datasheets.

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4


Technical data and ambient conditions

IMPORTANT The product-specific technical data, operating limits and ambient conditions for the operation of your Rexroth hydraulic product can be found in the Operating Instructions. This includes the following information: Ø

Minimum flow rate for adequate cooling

Ø

Permissible maximum temperature of the coolant

Ø

Performance data

Ø

Type of control and regulation functions

Ø

Permissible pressures, flow rates

Ø

Connections.

4.1

Information about pressure fluids

Unless otherwise indicated in the Operating Instructions, the following specification applies to the pressure fluid to be used: Ø Ø

Mineral-oil-based pressure fluid complying with the requirements of DIN 51524. Operating temperature range 0 °C…+80 °C (in tank < 72 °C).

Any deviations from this can be found in the Operating Instructions.

IMPORTANT Bosch Rexroth recommends a maximum operating temperature of 55 °C, because the rate of ageing of the pressure fluid increases and the service life of the seals and hoses is reduced at higher temperatures. Ø

Viscosity ranges: see RE 07075 and RE 90220

Ø

Max. permissible contamination class of the pressure fluid in accordance with ISO 4406: see 3.5.2 Malfunctions due to contamination of pressure fluid.

The maximum permissible cleanliness class can be found in the Operating Instructions. The following types of pressure fluids shall be used.

IMPORTANT Rexroth hydraulic components are tested with test oil MZ45 manufactured by ESSO (class ISO VG 46 at 40 °C), (Viscosity η = approx. 46 mm2/s).

Hydraulics

4.2

Bosch Rexroth AG

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Ambient conditions

4.2.1 Use in potentially explosive atmospheres

DANGER Rexroth hydraulic products shall be used in potentially explosive atmospheres only if they are designed for this purpose and this is expressly stated in the Operating Instructions.

IMPORTANT Directive 1999/92/EC of the European Parliament and Council dated 16 December 1999 concerning the minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres governs protection from danger from potentially explosive atmospheres. Observe the requirements contained in the regulations for operating equipment requiring supervision and the obligation to produce explosion protection documentation. This involves, for example, dividing areas endangered by potentially explosive atmospheres into zones and specifying suitable work equipment and procedures for these areas. Observe the requirements of Directive 94/9/EC of the European Parliament and Council dated 23 March 1994 on the approximation of laws of the member states concerning equipment and protective systems intended for use in potentially explosive atmospheres (ATEX Product Directive) and/or the corresponding national legislation by means of which the Directive was implemented in law in the EU member states. The directive contains requirements for the use of equipment and protective systems in potentially explosive atmospheres.

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Bosch Rexroth AG

Hydraulics

4.2.2 Climatic operating conditions Unless otherwise indicated in the Operating Instructions, the permissible ambient temperature Ø

for control units: 0 °C…+50 °C

Ø

for drive units with electric motors without heat exchangers, surface-cooled by free air circulation: 0 °C…+30 °C

Ø

for drive units with heat exchangers: < +40 °C.

Unless otherwise specified, Rexroth hydraulic products are designed for use in temperate climate zones and in covered areas (not in the open air) at relative air humidities of < 70 % and at room temperatures of 22 °C.

IMPORTANT For systems with oil-air heat exchangers: Observe the information given in the circuit diagram in the Operating Instructions.

In relation to the electronic equipment, the permissible ambient conditions apply to installed and protected electrical connections of class IP 55. Ø

Ambient temperature +5 °C…+40 °C assuming that the average air temperature over a 24 hour period does not exceed +35 °C.

Ø

Relative air humidity: 23…95 %, non-condensing.

Ø

Altitude: up to 1000 m above national datum.

DANGER Rexroth hydraulic products shall not be used in aeronautical equipment, except where they have been specially approved and appropriately labelled to this effect.


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5

5.1


What you need to know about pressure fluids

Hydraulics

Bosch Rexroth AG

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IMPORTANT Observe the following rules of thumb: At pressure fluid temperatures >70 °C, the rate of ageing doubles for each 10 °C.

How to handle pressure fluids safely 5.3

Viscosity

DANGER Mineral-oil-based pressure fluid is hazardous to water and flammable. It may only be used if the relevant safety datasheet from the manufacturer is present and all the measures stipulated therein have been implemented.

5.3.1 Viscosity grades The most important characteristic of a pressure fluid is its viscosity, i.e. stickiness. Viscosity range always plays a priority role in the selection of a pressure fluid. Viscosity is measured in the SI unit [mm2/s]. Many manufacturers still provide their information in centiStoke [cSt], the equivalent of [mm2/s].

5.2

Functions and effectiveness

Due to the many tasks of pressure fluid, its selection, inspection and maintenance are of vital importance for: Ø

proper functioning

Ø

operating safety

Ø

service life

Ø

and the cost effectiveness of the hydraulic product.

The tasks of pressure fluid: Ø

to transmit hydraulic energy from the pump to the hydraulic cylinder/motor

Ø

to lubricate parts moving against one another

Ø

corrosion protection

Ø

to remove contaminants

Ø

to remove locally accumulated heat.

5.2.1 Reduced function due to ageing The effectiveness of pressure fluid diminishes as it ages (undergoes chemical changes). Acids and resinous residues form, which may cause valve spools to stick. The following factors accelerate the ageing process: Ø

high temperatures

Ø

oxygen in the pressure fluid

Ø

air humidity

Ø

water

Ø

metallic catalysers

Ø

operating pressure

Ø

contaminants.

The viscosity grades (VG = viscosity grade) in accordance with ISO 3448 relate to the viscosity at 40 °C. The viscosity grade is appended to the type designation or the commercial name of the pressure fluid. Example: A pressure fluid with a viscosity grade of ISO VG 46 has a viscosity of 46 mm2/s at 40 °C. The relationship between medium temperature and viscosity for hydraulic oil (example) Medium temperature 3 °C 8 °C 25 °C 60 °C 77 °C

Viscosity 800 mm2/s 500 mm2/s 100 mm2/s 20 mm2/s 12 mm2/s

Too high a viscosity leads to the formation of air and vapour bubbles as a result of low pressure (cavitation). Too low a viscosity leads to increased leakage losses. Increased leakage losses cause the pressure fluid to heat up more, leading in turn to a further reduction in viscosity. The pressure fluid then loses its ability to lubricate. Valves, pumps and hydraulic motors, in particular, require exact compliance with the defined viscosity ranges. For certain ambient and operating temperatures, not all the requirements can always be covered with the available ranges of the viscosity grades. In order to comply with all the requirements, high viscosity pressure fluids with viscosity index improvers or a pressure fluid cooler/heater may be used.

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5.4

Bosch Rexroth AG

Hydraulics

Leakage fluid

Clearances and play mean that some leakage fluid escapes from all hydraulic products. Leakage fluid can be lead away internally or externally, depending on the component. It can be fed back into the tank or must be disposed of.

CAUTION Make sure that the leakage fluid is fed back into the tank in a proper manner. Dispose of leakage fluid that is not fed back into the tank properly, in compliance with the applicable environmental protection regulations.

5.5

Topping up/refilling

CAUTION When topping up/refilling your hydraulic system, make sure that you use pressure fluid of the same sort and type and from the same manufacturer. If the fluid is heavily contaminated or prematurely aged, then the system, including the tank must be cleaned and flushed before refilling. New pressure fluid must always be filtered in accordance with the required cleanliness class, as it does not normally meet the required cleanliness class in the as-supplied state.


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6

6.1


Bosch Rexroth AG

Hydraulics

Construction and mode of operation of a hydraulic system

9


8

Hydraulics (fluid technology)

7

Transmission, control and distribution of energy and signals using a pressurised fluid medium.

6

Hydraulic system

5

Arrangement of interconnected components for transferring and controlling hydraulic energy.

4 3

Component A single unit (e.g. a valve, filter, cylinder, motor) that consists of one or more parts and which is a functional constituent of a hydraulic system.

Drive A component that converts the energy of the hydraulic fluid into mechanical energy (e.g. motor, cylinder).

6.2

Schematic

In a system operated with hydraulic oil, first of all mechanical energy is converted into hydraulic energy, transported and controlled in this form, to finally be converted once more into mechanical work. The hydraulic elements are arranged in accordance with these functions. The following diagram shows a schematic representation of the elements of a complete hydraulic system. To demonstrate their operating principle, standardised symbols (ISO 1219) are used instead of sectional diagrams of the various devices. Line connections are represented by simple lines, as can be seen in the example.

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2 1 1

Tank

2

Filter

3

Pump

4

Pressure limiting valve

5

Directional valve

6

Check valve

7

Throttle valve

8

Hydraulic cylinder

9

Hydraulic motor

6.3

Oil preparation Energy conversion

Energy control

Energy conversion

Safety concept

Hydraulic products contain sensors and actuators, the interaction of which is particularly important with regard to the fulfilment of technical safety functions. Individual hydraulic products form part of an overall safety concept. Applications required to perform safety functions are designed using special hydraulic components that satisfy the requirements of the relevant directives, such as the Pressure Equipment Directive and other standards. The manufacturer of the overall machine or system defines and bears responsibility for the safety category to EN 954-1 to be fulfilled.

IMPORTANT A more detailed description of the safety concept and the specific safety components installed can be found in the Operating Instructions and the Operating Instructions of the supplier of the overall system in which the hydraulic product is installed.

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7

Bosch Rexroth AG

Hydraulics

Moving hydraulic units/components

Hydraulic units or components may be moved by a fork-lift truck or a hoist, depending on their size and the local conditions.

IMPORTANT For details see the Operating Instructions.


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IMPORTANT The factory-applied corrosion protection is adequate provided that Ø

no condensation or leakage water can enter the system

Ø

long standstills are avoided.

Contact Bosch Rexroth if you are not clear about the consequences of long standstills on the state of the hydraulic product.

CAUTION Always ensure hydraulic products are empty of pressure fluid for transportation. Rexroth hydraulic products are delivered empty of pressure fluid. However, products may contain oil residues left over from the final inspection at our factory.

8

Storage and longer standstills

8.1

Hydraulic systems - subsequent bringing into use after storage

Corrosion, especially oxidation, can cause metal surfaces to lose the standard of surface finish required for the hydraulic system to function properly. Rust and other metallic and non-metallic particles lead to abrasive wear (erosion), which detrimentally affects the functioning of the hydraulic system.

CAUTION If a hydraulic system is to be brought into use again following a long standstill, it must first be flushed clean.

8.1.1

Factory-applied corrosion protection

Rexroth hydraulic products are tested in accordance with Class III using a hydraulic oil that has additional anti-corrosive properties. The film of oil that remains in the product after the test provides sufficient internal corrosion protection. This factory lubrication ensures that valves do not stick during subsequent use of the hydraulic product, and guarantees compatibility with seals and the pressure fluid to be used.

8.1.2 Storage times in relation to the ambient conditions Delays in bringing into use, long shipping and storage times or long periods of non-use can lead to rust formation in Rexroth hydraulic products. Additional corrosion protection measures must be implemented to prevent this.

IMPORTANT If all the openings on the hydraulic products are not sealed so as to be air-tight, this will reduce the storage life of the hydraulic product by nine months. After the specified storage time has expired, in any event not longer than 24 months, the corrosion protection must be checked and further conservation measures applied if necessary.

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8.2


Seals, hoses and hose lines

CAUTION Seals: Observe the requirements of ISO 2230 and/or DIN 7716 and the specific manufacturer’s data on seals. Hoses and hose lines: In the Federal Republic of Germany, please observe the requirements of DIN 20066, ZH 1/74 Safety rules for hydraulic hose lines and the specific manufacturer’s data on hoses and hose lines. In addition, the following conditions shall be observed: Ø

Seals, hoses and hose lines are stored in cool, dry and dust-free conditions.

The hoses and hose lines can be enclosed in plastic foil to ensure low-dust storage conditions. Ideal storage conditions for hoses and hose lines are temperatures from +15 °C to +25 °C and a relative humidity of below 65 %. Ø

Do not store elastomers below –10 °C. The ideal storage conditions for seals are temperatures from +10 °C to +20 °C and a relative humidity of between 65 % and 75 %.

Ø

Store hoses and hose lines in the original packaging if possible. Prevent the entry of air.

Ø

Avoid direct sunlight and UV radiation and shield from nearby sources of heat.

Ø

Darkened storage locations are preferred.

Ø

Do not use ozone-forming light sources or equipment (e.g. fluorescent lamps, mercury-vapour lamps, copiers, laser printers) or electrical spark-forming devices in the vicinity of hoses and hose lines.

Ø

Seals, hoses and hose lines must not come into contact in particular with materials or vapours that could damage them (e.g. acids, alkalis, solvents).

Ø

Store seals, hoses and hose lines lying down and free from tension. If the hoses and hose lines are coiled, take care not to bend them to less than the smallest bending radius specified by the manufacturer.

Maximum storage times Ø

NBR seals: 4 years

Ø

FKM seals: 10 years

Ø

Hoses: 4 years

Ø

Hose lines: 2 years

For reasons of safety, seals, hoses/hose lines shall not be used once these permissible storage times are reached or exceeded. Permissible storage times could be considerably reduced if the permissible storage conditions are not maintained. If you are not clear about the storage times and/or storage conditions then you should not use the product.

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9

Bosch Rexroth AG

Hydraulics

Assembly and bringing into first use

IMPORTANT


RE 07008

Bringing into (first) use shall only be done by an instructed, authorised hydraulics expert who has the required specialist knowledge.

Only the permissible pressure fluids given in the Operating Instructions are to be used. Information on other pressure fluids can be found in the Operating Instructions or are available on request.

Specialist hydraulics knowledge means, among other things, that the person can read and fully understand hydraulics drawings. In particular, he must fully comprehend the range of functions of the integrated safety components as part of the overall safety concept.

Filling the pressure fluid tank must always take place through a suitable filter unit. Experience has shown that even new pressure fluid can often have more than the maximum permissible level of contamination.

9.2

All information specific to assembly and bringing into first use can be found in the Operating Instructions.

1.

Check the scope of delivery for transport damage.

Pay attention to cleanliness:

2.

Check that the Operating Instructions for the Rexroth hydraulic product are present and complete. Contact us if the Operating Instructions are not there or are incomplete.

3.

Assemble the hydraulic product.

Ø

Do not use cleaning wool or cloths containing fibres for cleaning. Depending on the condition of the system or machine, cleaning with fibre-free cloths may be sufficient. Use suitable liquid cleaning agents to remove lubricants and other stronger contaminants. Make sure that cleaning agent does not get into the hydraulic system.

Ø

•

Observe the Operating Instructions and this product information.

•

Assemble the hydraulic components, so that they are mounted strain-free on even surfaces.

•

Tighten the fastening bolts evenly using the specified tightening torque.

Never use hemp and putty as sealants.

The functional or failure behaviour of identical hydraulic products may vary due to conditions specific to the machine or system in which the hydraulic product is installed (mass, speed, electrical triggering at setpoint values, etc.), see also Section 11 Trouble-shooting.

9.1

Before bringing into first use

4.

Ensure that the interfaces of the system/machine and the installation conditions provide for safe operation of the hydraulic product. If in doubt, consult the people responsible for the overall system/functional machine.

5.

Check the construction of the hydraulic product against the circuit diagrams, lists of equipment and assembly drawings. If there are any differences, draw this to the attention of the people responsible. If important documents are missing, they can be requested from Bosch Rexroth. Only documents issued by the bodies authorised to do so shall be used.

6.

Based on the Operating Instructions for the system or machine in which the hydraulic product is installed, check whether bringing the hydraulic system into use could lead to uncontrolled, dangerous movements. Where appropriate, take into account the hazard analysis/risk assessment for the system or machine.

7.

Take the precautions appropriate to the anticipated dangers, e.g.

Safety advice for assembly and bringing into first use

DANGER Hydraulic products are generally intended for installation in machines/systems or devices. The function of the hydraulic product must therefore always be seen in relation to the function of this machine – i.e. seemingly identical hydraulic products may demonstrate different functional behaviours as a result of the function of the machine in which they are installed. For this reason, a hydraulic drive must not be brought into use until it has been determined that the machine in which it is installed conforms to EU standards. Do not bring hydraulic drives into use until you have familiarised yourself completely, firstly with the function of the hydraulic product and hydraulic equipment and secondly with the hydraulically powered machine functions, and have clarified and dealt with any possible dangers.

•

Ensure that the cylinder piston rod can move out without danger.

•

Use a hoist or other lifting device to additionally secure lifted loads.

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8.


As part of bringing into (first) use, check whether the electric motors and valve solenoids can be switched manually using the electrical controls of the system/machine. If they cannot be switched manually – or can but with difficulty – you must provide a remote control (e.g. test boxes for Rexroth proportional valves) for the internal function test of the hydraulic system.

IMPORTANT Starting up the hydraulics solely by means of emergency manual operation is not recommended, as several valves at once cannot be switched as required in the correct sequence. 9.

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Bringing into first use, subsequent bringing into use

DANGER Before bringing into (first) use, have all pressure accumulators and safety systems checked by an expert or specialist in accordance with national regulations. 1.

Clean the lock on the transport and storage container before opening.

Draw up a sequential program for bringing into (first) use and store it with the technical documentation as an appendix to the Operating Instructions. For this you should consider the following: Hydraulic drives basically consist of the following functional groups

2.

Clean the hydraulic unit and all other component groups, so that no dirt can get into the hydraulic system during bringing into (first) use.

3.

Check the paint on the tank for integrity.

4.

Flush the connection lines to remove dirt, scale, chips etc.

Ø

Pump circuit (generation of pressurised oil flow); pump, electric motor, oil tank, filters, monitoring devices, etc.

5.

Pickle and flush welded pipes.

Ø

Control system for at least one hydraulic consumer (cylinder, motor); directional control valves, pressure and flow control valves, check valves

Ø

Hydraulic consumers (cylinders, motors) with specially assigned valves, e.g. braking valve.

CAUTION Remove all residues of water and cleaning agents before performing further work.

6.

10. Divide the functional circuit diagram into separate mini-circuits that can each be started up in succession.

Clean the interior of the hydraulic components to get rid of contaminants: •

Clean the filler plug of the pressure fluid tank.

11. Read the functional circuit diagram and seek clarification of any unclear text or diagrams. More information about the functioning of components, e.g. a pump regulator, is available in the Technical Datasheet.

•

Remove dust and chips using an industrial vacuum cleaner, by rinsing parts or similar cleaning method.

•

Completely remove any oil residues left over from the factory test.

12. Establish into which position valves are to be switched, or how valves are to be set.

•

Remove any gummed oil which may have formed due to incorrect storage.

13. Put up any necessary directional, prohibitive or informative signs and check whether the meaning of these signs are explained in the Operating Instructions.

7.

IMPORTANT

14. Follow this sequence for bringing into (first) use Ø

Pump circuit

Ø

Parts of control system: e.g. pressure cut-off and switchover, open centre, pressure reduction etc.

Ø

Cylinder and motor circuits: First move, fill and bleed, then finally optimise all settings.

Connect up all connection lines.

Observe the installation instructions from the manufacturer of the connection components.

DANGER Make sure that pipes and hoses are connected at all ports or that the ports are sealed with screw plugs. 8.

Carry out a special check to make sure that the union nuts and flanges are correctly tightened at the pipe connections and flanges.

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Hydraulics


IMPORTANT

CAUTION

Mark all the checked connections, e.g. with paint. Make sure that all pipes and hoses and every combination of connection pieces, couplings or connection points with hoses or pipes are checked for their operational safety by someone who has the appropriate knowledge and experience. 9.

Connect the hydraulic consumers. Dimension the connection lines in accordance with the performance data in the Circuit Diagram and the Operating Instructions.

10. Install the electrical system for the drive and control system: •

Check the connected loads.

•

Connect coolant water if necessary.

•

Check the direction of rotation of the pumps (e.g. as indicated by attached arrow markings).

11. Check the pressure fluid to ensure that no water has entered it. 12. Before filling the pressure fluid tank, please observe the following requirements: Ø

The pressure fluid must conform to the specification in the Operating Instructions.

Use oil filler units (filter units) suitable for pressure fluids. •

Do not remove the filter strainers from filler necks or the filter element from filters before filling the pressure fluid tank.

13. Fill the pressure fluid tank up to the upper mark on the inspection window. Observe the maximum fluid level, taking into consideration the volume in the connection lines and hydraulic consumers. 14. Set the pressure and flow control valves, pump regulator, signalling elements such as pressure switches, limit switches and temperature regulators to the settings and values defined in the sequential program (see 9.2 Before bringing into first use).

DANGER Do not change the settings of valves with a safety function, valves with a position switch or valves with preset electronics. •

Set operating-pressure valves and flow control valves to the lowest possible values.

•

Set directional control valves to their basic setting.

•

Reduce the setpoint values of proportional valves to minimum values.

•

Do not remove the tamperproof lead seals. Damaged or removed tamperproof lead seals indicate improper use of the hydraulic product.

CAUTION Never fill new hydraulic products with used pressure fluid. Ø

The drums of pressure fluid must be sealed and clean on the outside.

IMPORTANT

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15. If applicable: Fill the pressure accumulator to the specified gas precharge pressure and then check the pressure, see Operating Instructions.

If the pressure fluid has a high level of initial contamination (see 4 Technical data and ambient conditions):

16. Fill the pump body: Use the leakage oil port to fill pump bodies that have this feature, see Operating Instructions.

Use a filter unit to fill the pressure fluid tank. Ensure that the filter element is clean.

17. If applicable: Open the cocks in the suction line.

IMPORTANT

18. Start the drive motors:

The fineness of the filter shall correspond to the cleanliness class required by the overall system and if possible be even finer. The filter unit used shall fulfil the requirements for functional safety and service life. •

If possible, fill the pressure fluid tank via a filling coupling, using a return filter if possible.

•

With electric motor in jogging mode, allow to start briefly

•

Combustion engines in idle

•

Pay attention to the direction of rotation.

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19. Bleed the hydraulics (valve, pump, motor, line, cylinder).

IMPORTANT Details on bleeding can be found in the Operating Instructions. •

Operate the hydraulic product at low pressure until it is fully bled.

•

Bleed the hydraulics lines to consumers or measuring points at the highest point, if possible.

•

Operate the directional valves in jogging mode.

•

Next, advance and retract all hydraulic consumers several times.

•

Increase the load slowly. Check the pressure fluid level in the pressure fluid tank. If necessary, top it up with pressure fluid.

Bleeding has been accomplished fully and correctly if the pressure fluid in the tank does not foam, if the hydraulic consumers do not make any jerky movements and if no abnormal noises can be heard. 20. Set the valves and sensors and start up the machine: •

•

Set the switching operations of valves with a switching time adjustment/ramp in accordance with the dynamic conditions, see Operating Instructions. Finely adjust and optimise the setting of proportional valves without on-board electronics (OBE).

Manufacturing tolerances mean that valves and amplifiers have to be adjusted in line with one another. Valves with in-built electronics (OBE, On Board Electronics) have the valve and amplifiers adjusted in line with one another at the factory. Amplifiers for valves without OBE are supplied from the factory with a basic setting. Depending on the type of valve and amplifier, you may have to fine-tune the null point and sensitivity before bringing the valve into use.

IMPORTANT Details on fine-tuning can be found in the Operating Instructions. 21. Check the operating temperature after the machine has been running continuously for several hours. Too high an operating temperature indicates that there are faults that need to be analysed and rectified. 22. Rectify any leakages, e.g. by relieving couplings from pressure and then retightening.

IMPORTANT Apart from moisture, which should not be sufficient to form one drop, no measurable, unintentional leakage shall be found.

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23. After bringing the machine into first use, have a sample of the pressure fluid analysed to ensure that it achieves the required cleanliness class. Change the pressure fluid if the required cleanliness class is not achieved. If the pressure fluid is not tested in the laboratory after bringing the machine into first use: Change the pressure fluid. 24. Replace the pressure fluid filter. 25. Document and file all set values.

DANGER 26. To ensure the safety of persons and the system, after bringing the machine into first use, perform the following tests using the defined maximum values: •

Function test

•

Pressure test.

Prepare a record of the bringing into (first) use or acceptance and have it signed by the plant operator. This record is an important document and requires to be filed.

IMPORTANT Information on how to perform the function test and pressure test can be found in the Operating Instructions.

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Hydraulics

Operation


Ø

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Is there a machine record book that may document similar malfunctions in the past?

IMPORTANT Please refer to the Operating Instructions for all information on how to operate the Rexroth hydraulic product.

11

Trouble-shooting

11.1 What to do in the event of a fault

11.2.2 Recommended way of working when trouble-shooting Successful trouble-shooting for a hydraulic product requires precise knowledge about the structure and method of operation of the individual components. Where hydraulics are combined with electrics/electronics, in particular, trouble-shooting is rendered more difficult and cooperation between electricians and hydraulic specialists is required. •

Even if you are under time pressure, proceed systematically and methodically. Indiscriminate, hasty dismantling and readjustments may, in the worst case, result in the original cause of failure being impossible to determine.

•

Make sure that you gain an overview of the function of the hydraulics in respect of the overall system in which the hydraulics are installed.

•

Try to find out whether the hydraulics performed the required function in the overall system prior to the occurrence of the fault.

•

Try to determine any modifications to the overall system in which the hydraulics are installed:

DANGER In the event of abnormal occurrences or malfunctions, stop all work on the Rexroth hydraulic product immediately and inform the responsible personnel.

IMPORTANT A table for product-specific trouble-shooting can be found in the Operating Instructions. If the responsible personnel are unable to rectify the problem immediately: •

Switch off the main switch. If applicable, turn off any combustion engines used as drive motors.

•


•

Inform the machine manufacturer.

11.2 The basic approach to trouble-shooting The information in this section is intended to help you create the ideal conditions for carrying out trouble-shooting as efficiently as possible.

11.2.1 General conditions

Ø

Have the operating conditions or operating range of the hydraulics been changed?

Ø

Have modifications (e.g. retrofitted equipment) or repairs been carried out on the overall system (machine/system, electrics, control system) or on the hydraulics? If yes: What were they?

Ø

Have the set values of the hydraulics been changed?

Ø

Have the hydraulics recently undergone maintenance?

Ø

Has the hydraulic product/machine been operated improperly?

Ø

How does the malfunction manifest itself?

•

Form a clear picture of the cause of the fault. Ask the machine operators directly, if necessary.

Ø

Is all the necessary technical documentation to hand?

•

Document any work undertaken, changed set values, etc.

Ø

If no hydraulic circuit diagram is available: Can a hydraulic circuit diagram be drawn using the structure, signs and labelling of the equipment?

•

Document any amendments/additional information that should be included in the Operating Instructions.

Ø

Are there enough measuring points?

Ø

Has the customer provided useful information about how the malfunction manifests itself and about the functional behaviour of the system/component prior to the malfunction?

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11.2.3 Systematic trouble-shooting procedure Ø

Ø

Is there an inspection and maintenance book which might provide information about the trend of test parameters (e.g. temperature of hydraulic fluid, replacement intervals of filter elements, noises)? Have there been any identical or similar failures in the past? •

Make a note of causes of failures with a low probability. Only investigate the failure causes you have noted down if all failure causes with a high probability have been proven to be inapplicable.

•

Draw up a list of priorities of the most probable failure causes.

•

Verify these listed failure causes one after the other (by means of theoretical conclusions, disassembly, measurements or tests).

•

Document the causes of failure you have discovered, and note down how you discovered them.

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11.3 Trouble-shooting tables

IMPORTANT The causes of failure in hydraulic systems can be extremely complex. Therefore, general rules for trouble-shooting can only be laid down to a limited degree. Please refer to the relevant Operating Instructions for product specific information about trouble-shooting the Rexroth hydraulic product.

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12

Bosch Rexroth AG

Hydraulics

Maintenance


RE 07008

Before undertaking any manual intervention in the Rexroth hydraulic product:

12.1 Definitions of terms

DANGER

The term Maintenance as defined in DIN 31051 encompasses all measures to maintain and restore the desired conditions and to determine and assess the actual condition of the technical devices of a system .

Please refer to the Operating Instructions for all the necessary information on depressurisation and on those parts of the Rexroth hydraulic product that are not depressurised automatically.

These measures are divided into the following categories:

•

Advance all cylinders to their safe end position.

Ø

Inspection (determining the actual condition)

•

Lower all loads.

Ø

Servicing (maintaining the desired condition)

•

Switch off all pumps.

Ø

Repair (restoring the desired condition).

•

Mechanically support vertical cylinders so that they cannot drop. Never perform any maintenance work on raised units without external support.

•

Relieve any accumulators of pressure in the proper manner.

•

Switch off the pressure supply and secure the hydraulic product against being inadvertently switched on again.

•

Ensure that only authorised personnel remain in the work zone.

•

Wear safety glasses, gloves and boots.

•

Allow pressure lines and sections of the system which have to be opened to cool down before commencing maintenance work.

•

Open with care any segments that have to remain under pressure.

The above measures include: Ø

Adapting maintenance objectives to suit company objectives

Ø

Determining appropriate maintenance strategies.

12.2 Safety during maintenance tasks

DANGER In the interests of safety, please observe all the following safety instructions carefully and at all times. •

Check safety devices regularly to see that they are working properly.

•

Perform all maintenance work properly, completely and within the stipulated periods and make a record of the work.

•

Inform all personnel before commencing maintenance work.

•

Generously cordon off the maintenance zone before commencing work.

•

Inform all persons of ongoing maintenance work by means of the appropriate signs. In particular, attach warning signs to the control cabinet, main switch, actuators and points of access.

If you have to switch off the hydraulic product, secure it against being unintentionally switched on again as follows: •

Switch off all drives, disconnect the hydraulics from the mains at the main switch.

•

Depressurise the hydraulic product (relieve any pressure accumulators of pressure).

•


Since check valves are located in the pressure lines above the pumps, the hydraulic system may still be under pressure even after it has been disconnected from the actual pressure supply. Certain segments, such as servo cylinders, also continue to remain under pressure because the proportional valves remain in the closed position (all valves are illustrated in their basic position in the hydraulics diagram). Observe the following: Ø

Only new, interchangeable and tested components, replacement parts and lubricants in original-equipment quality are approved for use/replacement.

Ø

For reasons of safety, the installation of used and/or untested components is strictly prohibited and leads to loss of EU Conformity.

Exercise extreme vigilance when operating the hydraulic product in maintenance mode, which may in certain circumstances necessitate the temporary removal of certain safety devices.

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Make sure that all safety devices are properly installed and have undergone a function test before bringing the system (back) into use. •

Perform welding, burning or grinding work on the hydraulic unit or its attachments only with the approval of local safety authorities/fire brigade and with suitable protective covering to prevent ingress of contaminants.

•

When performing assembly work above your height, use the steps and platforms provided by the plant operator. Do not climb on any parts of the system.

•

Remove all tools and materials needed for maintenance from the hydraulic product.

•

Always rectify any leakage from the hydraulic product immediately.

•

Always inform personnel before (re)starting the hydraulic product.

12.3 Inspection and servicing The objective of inspection and servicing is Ø

To maintain all system functions along with the initial parameters of the system

Ø

To ensure continual availability of the system

Ø

To detect weak points

Ø

To ensure that the system attains the required service life.

IMPORTANT The following general specifications are based on use of the hydraulic product in central Europe and under the usual operating conditions of commercial and industrial plants. We strongly recommend the use of an inspection and servicing book, in which all work specific to that site, and all inspection and servicing intervals should be defined and documented. An inspection and servicing book is also helpful in that Ø

It provides comparison values to aid with early detection of malfunctions

Ø

It allows warranty claims to be dealt with more easily.

CAUTION Ensure cleanliness during all work. •

Please observe the requirements for pressure fluids mentioned in Section 9 Assembly and bringing into first use.

•

Clean the external environment of couplings/joints and devices before disassembly. Do not use cleaning wool or cloths containing fibres for cleaning.

•

Seal all openings using protective caps.

•

Bleed the hydraulic product after each item of servicing work.

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•

Document and file details of any work undertaken, changed set values, etc.

•

Document and file details of any amendments/additional information that should be included in the Operating Instructions.

•

Modifications and additions could affect the validity of the EU Conformity Declaration/Manufacturer’s Declaration. Always consult Bosch Rexroth about any proposed modifications or additions.

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Hydraulics

12.3.1 Inspection procedures and test equipment, general The following are some of the typical inspection and testing procedures that are regularly used in connection with hydraulic systems and components.

IMPORTANT


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12.3.2 Location of testing and measuring points

IMPORTANT Please refer to the Operating Instructions for the installation location of filling level indicators, filling points, drainage points, filters, testing points, strainers, solenoids, etc. that require regular inspection and servicing.

Keep the indicated typical test equipment ready for this type of work. Type of test

Typical test equipment

Typical testing activities

Pressure measurement

Pressure gauge or sensor with suitable measuring range and connection pipe and connection coupling

Checking of

Visual inspection

–

•

specified pressure

•

opening pressure

•

pressure difference before and after the object under test

Temperature inspection

Acoustic inspection

–

•

all components securely seated

•

damage

•

wear

•

leakage (formation of oil droplets)

–

presence of all warning and informative signs

Checks for •

Temperature measuring instrument

The graph illustrates the concept of wear/wear margin. The wear margin is a characteristic feature used to describe the condition of the system for the purpose of maintenance. 5 ��

��

Checks for

•

Touch inspection

12.3.3 Inspection and servicing plan, hydraulic products, general

unusual local vibrations

Checks for •

unusual local temperature zones

Checks for •

changes in running noise of the unit

•

changes in flow noise

•

changes in operating noise in the unit and valve control.

1 4

�

�� 2

1 2

6 �� 3

Wear margin Z0 Time t

3

Repair (corrective maintenance) time (ti2 – ti1)

4

Damage threshold (damage time tS)

5 6

��

Desired condition after corrective maintenance Failure

The reduction in the wear margin reflects wear. The curve represents one possible form of the wear profile during the period of use. It is determined during inspection and varies depending, firstly, on the system itself (e.g. material selection, surface treatment, quality) and secondly on external influences or boundary conditions such as servicing levels, corrosive circulating air and dust. Thirdly, it depends on how the system is operated; whether with partial load or partially with excess load, whether it is subject to surge loads or steady load, etc. Where hydraulic systems are concerned, the curve is also influenced by the cleanliness class and degree of fouling of the pressure fluid, the number of cycles and the ambient conditions.

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All the factors mentioned above can exert an influence on the curve but this need not necessarily adversely affect the quality of its information, as wear always signifies the reduction in the wear margin, which is understood to be the primary initial variable before wear commences.

12.3.5 Inspection and servicing plan: electrics and control system

Consequently, this means that a sudden change in the wear margin must also count as wear, and that the element of time on its own is not of decisive importance for wear, but is of considerable interest in the assessment and evaluation of such wear.

The product-specific inspection and servicing plan for electrics and control systems can be found in the Operating Instructions.

An increase in the wear margin to over 100 % above its baseline may be achieved through corrective maintenance, if such measures entail an improvement and this increase is established as the new desired condition for future corrective maintenance. Certain system parts may be subject to a wear margin which diminishes in such a way that the time available for use is insufficient for the requirements of the plant or operation. In this case, investigations must be carried out to ascertain whether the introduction of suitable technical measures might counter this reduction in the wear margin to a satisfactory extent. The time and expenditure required for such measures must naturally be kept in reasonable proportion to the expected degree of success.

IMPORTANT

12.3.6 Lubrication points, lubricants, intervals

IMPORTANT The details of the specified lubricants, lubrication points and associated lubrication cycles can be found in the Operating Instructions.

12.3.7 Set values of valves, regulators and signalling elements

If such conditions arise, we refer to these parts as weak points. Since their elimination may provide economic and safety advantages, weak points require to be rectified immediately.

Pressure and flow control valves, pump regulators and signalling elements such as pressure sensors, pressure switches, limit switches and temperature regulators are given their optimum setting when the system is brought into first use.

IMPORTANT

Check regularly whether all values are correctly set with the aid of the hydraulics diagram and the documented values.

The inspection and servicing plan for your particular product can be found in the Operating Instructions.

12.3.4 Inspection and servicing plan, electrohydraulic systems Electrohydraulic systems with proportional valves must be serviced in accordance with hydraulic requirements and strategies. However, technical control components must also be incorporated in these servicing cycles. On this basis, an overall strategy for system servicing must be developed and documented.

IMPORTANT The appropriate component characteristics relevant to servicing can be found in the Operating Instructions.

DANGER The set values of valves with position switches shall only be calibrated or readjusted at the factory. The set values of safety valves shall not be altered by the user. Any readjustment shall be performed by authorised testing bodies only. Too low a pressure difference between the operating pressure and the opening pressure can lead to frequent opening of safety valves. This leads to increased power losses and an unacceptable increase in temperature of the pressure fluid. In this event, select a lower operating pressure.

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Hydraulics


12.3.8 Replacement of pressure fluid filters and ventilation filters

CAUTION Unfiltered pressure fluid filters lead to increased wear of all the system’s hydraulic products and can cause functional failures with dangerous effects. Therefore, always replace contaminated oil filters immediately. Clogged ventilation filters result in inadequate cooling and can therefore cause excessive heating up and malfunctions of the hydraulic system. Therefore, always replace contaminated ventilation filters immediately. •

Clogged filters must always be replaced immediately. Do not clean clogged filters.

•

Allow the contents of the replaced oil filter to drip and fully drain.

•

Dispose of the filter in accordance with the applicable regulations.

Exact instructions on how to replace a filter can be found in the Filter manufacturer’s instructions for use.

12.3.9 Checking filters with a contamination indicator Filters with contamination indicators continuously measure the degree of fouling. The dirt-retention capacity of the filter is utilized to the full.

IMPORTANT Check the contamination indicator when the pressure fluid is warm (during or immediately after operation). If the ambient temperature is low or the pressure fluid is cold, its high viscosity may cause clogging to be indicated, although the pressure fluid is in fact clean. Procedure: 1.

Wait until the hydraulic product has reached operating temperature.

2.

Press the indicator button (check function): If the indicator button pops out again immediately, the filter must be replaced by the end of the shift at the latest.

Due to the progressive loss in pressure as the filter becomes increasingly contaminated, the indicator point has a certain reserve capacity, i.e. generally sufficient for a work shift of 8 h. If the filter is not replaced after 8 h, dirt may penetrate the system, resulting in contamination of the hydraulic product.

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CAUTION In certain circumstances the contamination indicator does not show a required filter replacement. If the check function never indicates filter replacement and the contamination indicator is functioning correctly, this may have the following causes: Ø

Faulty filter

Ø

A bypass valve may have been installed and is not closing correctly, e.g. due to the entry of dirt particles.

12.4 Service and storage lives of hose lines

IMPORTANT In terms of the service life of hydraulic hose lines in these Operating Instructions, replacement and storage lives are measured from the date of manufacture of the hose line. Even when properly stored and subjected to permissible loads, seals, hoses and hose lines undergo a natural ageing process. The replacement and storage lives of seals, hoses and hose lines are therefore limited (see 8.2 Seals, hoses and hose lines).

DANGER Hose lines must be replaced in accordance with the provisions of the servicing plan, even if there are no detectable technical defects in the hose line. Hoses that have already been used as part of a hose line shall not be reused in a hose line. The first use may have changed the properties of the hose material to such an extent that reuse of the hose represents a very high risk.

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12.5 Topping up the pressure fluid

12.7 Repair

IMPORTANT

IMPORTANT

Only pressure fluids specified in the Operating Instructions are to be used.

Repair (corrective maintenance) is the restoring of the desired condition.

When changing or topping up the pressure fluid, fill the pressure fluid tank on the hydraulic product as follows:

In addition, observe the special safety instructions in 12 Maintenance and the safety instructions in the Operating Instructions.

1.

Fill the pressure fluid tank using a special filling unit with an integral filter (min. 10 µm).

2.

Drop the system pressure right down by resetting the pump. Set the pressure setting value on the pump pressure control to minimum or zero pressure.

3.

Fill and bleed the line system of the hydraulic product from the unit to the cylinder. To do this actuate the cylinder in both directions, see Operating Instructions.

4.

Top up the pressure fluid volume to the specified quantity.

5.

Raise the pump pressure to the system pressure.

The hydraulic product is ready for operation. 6.

Carry out a test run.

7.

Check the level of the fluid after the hydraulic product has warmed up to the operating temperature and adjust if necessary.

IMPORTANT Check the contamination indicator when the pressure fluid is warm (during or immediately after operation). If the ambient temperature is low or the pressure fluid is cold, its high viscosity may cause clogging to be apparently indicated.

12.6 Servicing pressure accumulators

DANGER Pressure accumulators are subject to the national legislation on safety requirements for pressure vessels applicable in the place of installation. Observe the Pressure Equipment Directive 97/23/EC.

IMPORTANT The gas precharge pressure is measured with a testing and filling device. Details of the procedure can be found in the Operating Instructions. Inspection and servicing •

Carry out the tests required by law.

•

Test and monitor the gas precharge pressure regularly.

DANGER Ensure cleanliness during all work. •

Clean the external environment of couplings/joints and devices before disassembly. Do not use cleaning wool or cloths containing fibres for cleaning.

•

Seal all openings using protective caps.

•

Bleed the hydraulic product after each item of repair work.

•

If appropriate, follow the procedure for bringing into first use, see 9.3 Bringing into first use, subsequent bringing into use.

•

Document any amendments/additional information that should be included in the Operating Instructions.

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12.7.1 General safety instructions for repair work

DANGER Repair work shall only be done by an authorised hydraulics expert who has the required specialist hydraulics knowledge. Specialist hydraulics knowledge means, among other things, that the person can read and fully understand hydraulics drawings. In particular, he must fully comprehend the range of functions of the integrated safety components. Components may only be dismantled for the purpose of repair to the extent described in the Operating Instructions. Never repair a defective safety valve. It must be completely replaced. Faulty parts may only be replaced by new, interchangeable, tested components in original-equipment quality. Any deviations from this can be found in the Operating Instructions. Before each subsequent bringing into use after repair work, the hydraulic product shall be accepted by a hydraulics expert. The operator of the hydraulic product is required to check by means of a servicing record that the inspection and servicing plan as been complied with. Pressure vessels have to be pressure tested every 10 years and the information recorded in accordance with the Pressure Equipment Directive 97/23/EC or its implementation in national legislation.

13

General information about hydraulic pressure accumulators

13.1 General The regulations applicable at the place of installation concerning hydraulic pressure accumulators (hydrostatic accumulators) must be observed before bringing into use and during operation. The plant operator bears sole responsibility for compliance with the existing regulations. Hydrostatic accumulators are subject to the national implementation of the EU Pressure Equipment Directive 97/23/EC. Documents supplied with accumulators must be preserved with care; they will be required during recurring inspections by specialists. The bringing into use of hydrostatic accumulators shall be carried out by trained expert personnel only.

RE 07008

WARNING Do not perform any welding, soldering or mechanical work on accumulator vessels. Welding and soldering carry a risk of explosion! Mechanical tampering may cause the vessel to burst and the operating permit will be withdrawn. Do not charge hydrostatic accumulators with oxygen or air. Risk of explosion! Depressurise the system before working on hydraulic installations. Improper installation can lead to serious damage to persons and property.

13.2 Safety devices relating to hydraulic pressure accumulators The equipping, installation and operation of hydrostatic accumulators is regulated by the national implementation of the EU Pressure Equipment Directive 97/23/EC and additionally in the Federal Republic of Germany by the Technical Regulations for Pressure Vessels (TRB). This legislation requires the following safety equipment: Ø

Device to protect against excessive pressure (prototype-tested)

Ø

Pressure relief device

Ø

Pressure measuring device

Ø

Test gauge connection

Ø

Shut-off device

Ø

Optional: electromagnetically operated pressure relief device

Ø

Safety device to protect against overheating.

IMPORTANT See the Operating Instructions.

RE 07008

14


Hydraulic systems

Hydraulic systems are generally intended for installation in machines or systems. In addition to the basic information about the installed components, the information contained in the Operating Instructions made available for each hydraulic system by Bosch Rexroth also applies to hydraulic systems. By installing the hydraulic system in a machine or system, the interaction of the hydraulic system with the overall machine may give rise to changes in the potential dangers. In particular the effect of hydraulic and electrical control of hydraulic drives that create mechanical movement are to be considered. This information shall be included in the hazard analysis/risk assessment of the overall machine carried out by its supplier and in the Operating Instructions of the overall machine. This also applies to the specification of the interfaces between the hydraulic system and the overall machine. Hydraulic systems are subject to legislation including the Pressure Equipment Directive and other relevant EU directives that have been implemented in national legislation. Exact information can be found in the EU Conformity Declaration or Manufacturer’s Declaration that is supplied with the hydraulic system or the hydraulic product.

WARNING Before installing a hydraulic system in a machine or modifying an existing hydraulic system in a machine, satisfy yourself that Ø

the hydraulic system is suitable for its application in the machine

Ø

the ambient conditions in the machine are suitable and/or permissible for the use of the hydraulic system

Ø

other installed items on or in the machine cannot disturb or endanger the functioning or the safe operation of the hydraulic system.

If the overall machine is to be used in a potentially explosive atmosphere, then it must be ensured that the hydraulic system has been designed and is suitable for this use.

Hydraulics

Bosch Rexroth AG

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14.1 Effects of leaks in the hydraulic system on the machine If pressure fluid escapes from the hydraulic system and comes into contact with hot surfaces on the machine, this can lead to the generation of life-threatening smoke, fire and/or other dangerous operating conditions. These risks shall be determined by the machine manufacturer by means of a hazard analysis and if necessary provision made for the appropriate safety devices.

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DE

Bestellinformation für deutsche Produktinformation:

RD 07008

EN

Ordering Information for Product Information in English:

RE 07008

FR

Information de commande pour la notice française Informations générales sur les produits :

RF 07008

IT

Informazioni d’ordine per le informazioni tedesche sul prodotto:

RI 07008

ES

Información para el pedido de la información del producto en español:

RS 07008

FI

Tilaustiedot - suomenkieliset tuotetiedot:

RSF 07008

NL

Bestelinformatie voor Nederlandse productinformatie:

RNL 07008

SV

Beställningsnummer för svensk produktinformation:

RSK 07008

PT

Informação dos dados de encomenda para informação de produto alemã:

RP 07008

DA

Bestillingsinformationer vedr. dansk produktinformation:

RDK 07008

EL

Πληρφρίε παραγγελία για τι γερµανικέ πληρφρίε πρϊντ:

RGR 07008

Hydraulics


RE 07008

http://www.boschrexroth.com/bri-products → Datenblatt-Suche/Datasheet search → Suche nach Datenblatt/Search by datasheet 07008

Bosch Rexroth AG Hydraulics Zum Eisengiesser 1 97816 Lohr am Main, Germany Tel. + 49 (0) 93 52 / 18-0 Fax + 49 (0) 93 52 / 18-23 58 [email protected] www.boschrexroth.de

© All rights reserved, Bosch Rexroth AG, including applications for intellectual property rights. We reserve all power of disposal, rights of reproduction and issue. The data specified above only serve to describe the product. No statements concerning a certain condition or suitability for a certain application can be derived from our information. The given information does not release the user from the obligation of own judgement and verification. It must be remembered that our products are subject to a natural process of wear and aging.

Bosch Rexroth AG Training Systems and Teachware Maria-Theresien-Straße 23 97816 Lohr a. Main, Germany Phone +49 9352 18-1041 Fax +49 9352 18-1040 [email protected] www.boschrexroth.com

© This document, as well as the data, specifications and other information set forth in it, are the exclusive property of Bosch Rexroth AG. It may not be reproduced or given to third parties wihout its consent. Made in Germany Document number: RE 00845/04.07 Material number: R961003790

Industrial hydraulics-MANUAL.pdf

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