Basic Hydraulic System

Malaysian Spanish Institute

Assembly & Maintenance Maintenance of Pneumatic & Hydraulic System (SED 23103) Basic Automation System (SRD 23403) v5

1

Assembly & Maintenance of Pneumatic & Hydraulic System (SED 23103) - (Assessment) 1. Basi Basic c Pne Pneum umat atic ic Syst System em

2.

Basic Hy Hydraulic Sy System

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Technical Report

10%

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Technical Report

10%

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Mini Project

10%

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Mini Project

10%

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Test

10%

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Test

10%

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Exam Practical

20%

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Exam Practical

20%

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Total Marks (SED 23103) –

Technical Report

20%

–

Mini Project

20%

–

Test

20%

–

Exam Practical

40%

100%

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2.


–

Technical Report

10%

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Technical Report

10%

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Mini Project

10%

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Mini Project

10%

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Test

10%

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Test

10%

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Exam Practical

20%

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Exam Practical

20%

•

Total Marks (SED 23103) –

Technical Report

20%

–

Mini Project

20%

–

Test

20%

–

Exam Practical

40%

100%

2


2.


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Pneumatic Power

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Hydraulic Power

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Pneumatic Control

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Hydraulic Control

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Pneumatic Actuator

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Hydraulic Actuator

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End of Course –

Comparison of Power System

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Selection of Power System

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Assembly & Maintenance of Pneumatic & Hydraulic System (SED 23103) (Study 1. Basic Pneumatic System

2.

Planning) Basic Hydraulic System

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Week 1 – 6 (Study week)

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Week 8 – 13 (Study Week)

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Week 7 (Practical Test)

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Extra Assessment Attitude marks 1. 2. 3. 4.

Attendant (per/minute = 0.019%) Cheating (per/cheat = 1%) Attire (per/day = 5%) Behavior (per/hour = 5%)

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Basic Automation System (SRD 23403) - (Assessment) 1.

2.

Basic Pneumatic System

3. Basic Electrical System

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Technical Report

7%

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Technical Report

6%

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Mini Project

7%

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Mini Project

6%

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Test

7%

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Test

6%

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Exam Practical

14%

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Exam Practical

12%

Basic Hydraulic System –

Technical Report

7%

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Mini Project

7%

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Test

7%

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Exam Practical

14%

• Total Marks (SRD 23403) –

Technical Report

7+7+6%

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Mini Project

7+7+6%

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Test

7+7+6%

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Exam Practical

14+14+12%

100%

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Basic Automation System (SRD 23403) - (Content Summary) 1. Basic Electrical System

3. Basic Hydraulic System

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Electrical Power

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Hydraulic Power

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Electrical Control

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Hydraulic Control

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Electrical Actuator

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Hydraulic Actuator

2. Basic Pneumatic System –

Pneumatic Power

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Pneumatic Control

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Pneumatic Actuator

• End of Course –

Comparison of Power System

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Selection of Power System

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Basic Automation System (SRD 23403) (Study Planning) 1. Basic Pneumatic System

3. Basic Electrical System

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Week 11 – 13 (Study Week)

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2. Basic Hydraulic System –


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• Extra Assessment – Attitude marks • Attendant (per/minute = 0.019%) • Cheating (per/cheat = 1%) • Attire (per/day = 5%) • Behavior (per/hour = 5%)

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Basic Hydraulic System

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Introduction to Didactic Unit • Objective of Module Why hydraulic system? Because: hydraulic system is amazing in its s t r e n g t h and agility . It is uses in medium and heavy application. It is a b a s i c c o n t r o l s y s t e m . Uses l i q u i d as its medium. Uses in m e d i u m and h e a v y application.

Why learn hydraulic system? Its a basic control system.

Why learn maintenance of hydraulic system? To describe the methodology of p r e v e n t i v e and c o r r e c t i v e maintenance technique of Hydraulic System. 9

•Basic Control System

signal input

pushbutton

signal processing

valve

output

cylinder

10

•Control & Maintenance

Assembly / Maintenance / Troubleshoot

signal input

signal processing

output

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Content of Module •

CHAPTER X INTRODUCTION TO DIDACTIC UNIT

•

CHAPTER 0 SAFETY IN HYDRAULIC SYSTEM

•

CHAPTER 1 INTRODUCTION TO HYDRAULIC SYSTEM

•

CHAPTER 2 FUNDAMENTAL IN HYDRAULIC SYSTEM

•

CHAPTER 3 TANK PIPING AND COUPLINGS

•

CHAPTER 4 HYDRAULIC PUMPS

•

CHAPTER 5 HYDRAULIC ACTUATOR

•

CHAPTER 6 DISTRIBUTOR VALVES

•

CHAPTER 7 PRESSURE VALVES

•

CHAPTER 8 FLOW VALVES

•

CHAPTER 9 BLOCK VALVES

•

CHAPTER 10 ELECTRO – HYDRAULIC SYSTEM

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Safety In Hydraulic System chapter 0

General safety High pressures, temperatures and forces occur in Hydraulic System. Energy is also stored, sometimes in large quantities. A whole series of safety measures is necessary to rule out the possibility of danger to personnel and equipment during the operation of hydraulic systems. In particular, the valid safety regulations for hydraulic systems are to be OBSERVED.

13

Regulations and standards The following safety regulations apply for the field of hydraulics: 1.

Accident prevention regulations, directives, safety rules and the testing guidelines,

2.

Regulations on pressure vessels, pressurized gas vessels and filling systems (pressure vessel regulations),

3.

DIN standards, VDI directives, VDMA standard sheets and technical rules for pressure vessels, containing in particular, notes and regulations on dimensions, design, calculations, materials and permissible loads as well as conditions on functions and requirements.

4.

Electro-hydraulic systems must comply not only with the regulations on hydraulic systems but also with the regulations on electrical systems and components (e.g. DIN VDE 0100).

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Safety Recommendations •

Install the EMERGENCY STOP push-button in a place where it can be easily reached.

•

Use standardized parts only.

•

Enter all alterations in the circuit diagram immediately.

•

The rated pressure must be clearly visible.

•

Check whether the installed equipment can be used at the maximum operating pressure.

•

The design of suction lines should ensure that no air can be drawn in.

•

Check the oil temperature in the suction line to the pump. It must not exceed 60 °C.

•

The piston rods of the cylinders must not be subjected to bending loads or lateral forces. Protect piston rods from dirt and damage.

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Start-up of Hydraulic System •

Do not operate not operate systems or actuate switches if you are not totally not totally sure what sure what function they perform.

•

All setting values must be known.

•

Do not switch on the power supply until all lines are connected.

•

Important: Important: check that all return lines (leakage lines (leakage lines) lead to the tank.

•

When starting up the up the system for the first time, open the system pressure relief valve almost completely and gradually set the set the system to the operating pressure. pressure. Pressure relief valves must be installed in such a way that they cannot become ineffective.

•

Carefully clean the system prior to start-up, then change the filter cartridge.

Vent system and cylinders. •

In particular, the hydraulic hydraulic lines to the reservoir are to be carefully vented. It is generally possible to effect venting at the safety and shut-off block of the reservoir.

•

Special care is needed when handling hydraulic reservoirs. reservoirs.

•

Before the reservoirs are started up, the regulations determined by the manufacturer are to be studied carefully.

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Repair and Maintenance • Repair work may not be effected on hydraulic systems until the fluid pressure of the reservoir has been release. release. If possible, separate the reservoir from the system (using a valve). Never drain the reservoir unthrottled. • When repairs are completed effect a new start-up in line with the safety regulations listed above. • All hydraulic reservoirs are subject to the provisions of the pressure vessel regulations and must be inspected at regular intervals.

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General Lab rules 1.

You are prohibited from entering Hydraulic Lab without SAFETY BOOT (all BOOT (all time), DUST COAT (practical uses)

2.

Do not be afraid to ask questions. questions. We are here to assist you.

3.

Do not step on step on any signal or actuator controller cable.

4.

Never use your finger to align boltalign boltholes.

5.

You must keep must keep your work area clean and clean and free of rubbish. rubbish.

6.

Never place any part of your body in in an area that is considered a crush point.

7.

If you break or break or notice any notice any defects in the equipment you are using, immediately inform the TTO. TTO. This ensures that you will not be held responsible for repairing the equipment.

8.

Do not leave tools on load frames or specimens, and at the end of the day put all tools back where they belong.

9.

Work methodically and methodically and at a steady pace, and do not be afraid to ask your fellow students or Mr. FATHU FATHUL L to assist you.

10.

USE COMMON SENSE.

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Introduction to Hydraulic System chapter1

Hydraulic means the generation of forces and motion using hydraulic fluids. Hydraulic fluids represent the medium for power transmission. Advantage of hydraulic system

Disadvantage of hydraulic system

•Great power intensity

•Pollution

•Precise positioning

•Sensitivity to dirt

•Start-up under heavy load

•Danger resulting from excessive pressures

•Independent of load

•Temperature dependence

•Smooth operation and reversal

•Unfavorable efficiency factor

•Good control and regulation •Favorable heat dissipation 19

Application Of Hydraulic System • Stationary Hydraulic (Vise, clamp, stamping machine, injection moulding machine, and etc).

• Mobile Hydraulic (bulldozers, backhoes, shovels, loaders, fork lifts, cranes and etc).

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Hydraulic System Overview

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Hydraulic System vs. Pneumatic System Drive section Control section Power section

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Schematic Diagram Of A Hydraulic System

Single Acting Cylinder

Double Acting Cylinder

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The Basic Idea The basic idea behind any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. The picture below shows the simplest possible hydraulic system:

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Working Principle

Retract position

Extend position

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Fundamental in Hydraulic System Chapter 2

1.

Pressure

7. Pressure Measurem rement

2.

Pressure Transmission

8. Type of Flow

3.

Power Tr Transmission

4.

Displacement Transmission

9. Fri Friction tion,, hea heat & pre pressure sure drop 10. 10. Ener Energy gy & Pow Power er

5.

Pressure Transfer

11. Power

6.

Flowrate

12. 12. Cavit Cavitati ations ons & Thrott Throttle le point 13. 13. Hydr Hydrau aulilic c Fluid Fluid

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1. Pressure • Pressure (symbol: Pressure (symbol: p p)) is the f o r c e per per unit area acting on a surface in a direction p e r p e n d i c u l a r to that surface. • Mathematically:

F

A

p

where:

Area of double acting cylinder = π (d/2)² 27

example

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2. Pressure Transmission •

•

If a force F1 acts at area A1 on an enclosed liquid, a pressure p is produced which extends throughout the whole of the liquid (Pascal’s Law). This will cause a same pressure acting at every point of the closed system.

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example

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3. Power Transmission • If same pressure applies at every point in a closed system, the shape of the container has no significance. significance.

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example

Therefore

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4. Displacement Transmission •

If load F2 is to be lifted to a distance s2, Piston 1 must be displace at distance s1, at a specific quantity of liquid which lifts the Piston 2 by a distance s2.

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example

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5. Pressure Transfer •

The pressure P1 exerts F1 force on area A1 which is transferred thru piston rod onto the small piston. Force F1 will acts on area A2 and produces pressure P2. Since piston area A2 is smaller than piston area A1, the pressure P2 wil l be greater than the pressure P1.

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example

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6. Flowrate • •

Flow rate is the term used to describe the volume of liquid flowing through a pipe in a specific period of time. For example, approximately one minute is required to fill a 10 liter bucket from a tap. Thus, the flow rate amounts to 10 l/min.

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6. Flowrate Other derivation

We’ll have

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7. Pressure Measurement •

To measure pressures in the lines or at the inputs and outputs of components, a pressure gauge is installed in the line at the appropriate point.

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8. Type of flow

1. Laminar flow fluid moves through the pipe in cylindrical layers order.

2. Turbulence flow when flow velocity of fluid rises above a certain point the fluid particles s t o p to move in ordered layers.

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Reynolds’ number (Re). • A method of calculating the type of flow in a smooth pipe is enabled by the Reynolds’ number (Re). This is dependent on: • the flow velocity of the liquid v (m/s)  (flowrate) • the pipe diameter d (m) • and the kinematics viscosity

(m²/s)

 (viscosity)

laminar flow: Re < 2300 turbulent flow: Re > 2300

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Reynolds’ number (Re). • The value 2300 is termed the “critical Reynolds’ number” (Recrit) for smooth round pipes. • Turbulent flow does not immediately become laminar on falling below (Recrit). The laminar range is not reached until ½ (Recrit). • To prevent turbulent flow causing considerable friction losses in hydraulic systems, (Re crit) should not be exceeded.

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Example:

3

1

1. Draw line from piping dia. to liquid flow velocity(1-2) 2. From point (2) draw a line to flowrate in the pipe, (2-3) 3. The Reynolds’ number are on point (4)

4

2

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Guideline Hydraulic flowrate

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9. Friction, Heat & Pressure droop • • •

•

Friction occurs in all devices and lines in a hydraulic system. Mainly at the line walls (external friction and between the layers of liquid (internal friction). The friction causes heat. As heat generation, the pressure in the system drops and reduces the actual pressure at the drive section. The size of the pressure drop is based on the internal resistances in a hydraulic system. These are dependent on: – Flow velocity (cross-sectional area, flow rate), – Type of flow (laminar, turbulent), – Type and number of cross-sectional reductions in the system of lines (throttles, orifices), – Viscosity of the oil (temperature, pressure), – Line length and flow diversion, – Surface finish, – Line arrangement.

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10.Energy & Power • The energy of a hydraulic system is made up of several forms of energy. – Static • Potential energy • Pressure energy

– Dynamic • Motion energy • Thermal energy

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Type of Energy •

Static – Potential energy: energy which a body (or a liquid) has when it is lifted by a height h. – Pressure energy: pressurized volume

•

Dynamic – Motion energy: when a force F acting on the body that moves at a certain speed. (also known as kinetic energy) – Thermal energy: is the energy required to heat a body (or a liquid) to a specific temperature. • In hydraulic installations, part of the energy is converted into thermal energy as a result of friction. This leads to heating of the hydraulic fluid and of the components. Part of the heat is emitted from the system, i.e. the remaining energy is reduced. The consequence of this is a decrease in pressure energy.

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11.Power • Power is usually defined as work or a change in energy per unit of time. • Hydraulic power is calculated from the pressure and the flow rate.

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Example

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Efficiency •

The input power in a hydraulic system does not correspond to the output power since line losses occur. The ratio of the output power to the input power is designated as efficiency (h).

•

In practice, distinction is made between volumetric power loss caused by leakage losses and hydro-mechanical power loss caused by friction. In the same way, efficiency is divided into: – Volumetric efficiency (ŋvol): This covers the losses resulting from internal and external leakage losses in the pumps, motors, and valves. – Hydro-mechanical efficiency (ŋhm): This covers the losses resulting from friction in pumps, motors, and cylinders.

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Example

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12. Cavitations & Throttle point •

•

•

Refers to the releasing of the smallest particles from the surface of the material. Motion energy is required for an increase in flow velocity of the oil at a narrowing. This motion energy is derived from the pressure energy. Because of this, pressure drops at narrow points may move into the vacuum range. From a vacuum of 0.3bar onwards, dissolved air (Gas bubbles) are formed. If the pressure now rises again as a result of a reduction in speed, the oil causes the gas bubbles to collapse.

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13.Hydraulic Fluid Hydraulic fluids represent the medium for power transmission. Function – Pressure transfer – Lubrication for moving parts / devices – Cooling agent: - diversion of heat produced by energy conversion – Cushioning of oscillations cause by pressure jerks. – Corrosion protection – Scuff removal – Signal transmission

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Characteristic of hydraulic fluid • • • • • • • •

•

lowest possible density minimal compressibility viscosity not too low (lubricating film) good viscosity-temperature characteristics good viscosity-pressure characteristics good ageing stability low flammability good material compatibility

example of hydraulic fluid – HLP 68 • • • •

H:- hydraulic fluid, L:- with additives to corrosion protection and/or ageing stability, P:- with additives to reduce and/or increase load carrying ability 68:- viscosity code as defined in DIN 51517

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Viscosity • can be defined as “resistance to flow”. The viscosity of a liquid indicates its internal friction.

Ball Viscometer 55

Tank, Piping & Coupling Chapter 3

Tank / Reservoir • • • •

acts as intake and storage reservoir for the hydraulic fluid required for operation of the system; dissipates heat; separates air, water and solid materials; supports a built-in or built-on pump and drive motor and other hydraulic components, such as valves, accumulators, etc.

Reservoir size, dependent on: • • • • •

pump delivery the heat resulting from operation in connection with the maximum permissible liquid temperature the maximum possible difference in the volume of liquid which is produced when supplying and relieving consuming devices (e.g. cylinders, hydraulic fluid reservoirs) the place of application the circulation time.

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Tank / Reservoir Reservoir shape • High reservoirs are good for heat dissipation, wide ones for air separation. Intake and return lines • These should be as far away from one another as possible and should be located as far beneath the lowest oil level as possible. Baffle and separating plate • This is used to separate the intake and return areas. In addition, it allows a longer settling time for the oil and, therefore, makes possible more effective separation of dirt, water and air . Base plate • The base of the tank should slope down to the drain screw so that the deposited sediment and water can be flushed out. Ventilation and exhaust (air filter) • To balance the pressure in case of a fluctuating oil level, the reservoir must be ventilated and exhausted. For this purpose, a ventilation filter is generally integrated into the filler cap of the feed opening.

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Piping (Flexible Hoses) •

These are flexible line connections which are used between mobile hydraulic devices or in places where there is only limited space (particularly in mobile hydraulics).

The inner tube (1) is made of synthetic rubber , Teflon, polyester-elastomer, perbunan or neoprene. The pressure carrier is a woven intermediate layer of steel wire and/or polyester or rayon. This woven section (2) may consist of one or more layers depending on the pressure range. The top layer (3) is made of wear-resistant rubber, polyester , polyurethane elastomer or other materials. The pipelines may be additionally protected against mechanical damage by external spirals or plaited material.

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Installation of Hose Lines

59

Coupling Hose lines may either be connected to the various pieces of equipment or else connected together by means of screw fittings or quick connection couplings. Hose support connectors ensure that connections do not affect operation:

60

HYDRAULIC PUMP Chapter 4

•

The pump in a hydraulic system, also known as a hydraulic pump, converts the mechanical energy in a drive unit into hydraulic energy (pressure energy).

•

The pump draws in the hydraulic fluid and drives it out into a system of lines.

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The Basic Concept

High pressure

Low pressure

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TYPE OF HYDRAULIC PUMP Hydraulic pumps

Gear Pump

Rotary Vane Pump

Piston Pump

External Gear Pump

Single Chamber

Radial Piston Pump

Internal Gear Pump

Double Chamber

Axial Piston Pump

63

TYPE OF HYDRAULIC PUMP

External Gear Pump

Double Chamber

Internal Gear Pump

Single Chamber

Radial Piston Pump

Axial Piston Pump

64

Gear Pump: Working Principle

Volume increase

To hydraulic system

To hydraulic system

From tank

From tank

Volume increase

External gear

Internal gear 65

Working Operation (Gear Pump)

The suction area S is connected to the reservoir. The gear pump operates according to the following principle: One gear is connected to the drive, the other is turned by the meshing teeth. The increase in volume which is produced when a tooth moves out of a mesh causes a vacuum to be generated in the suction area. The hydraulic fluid fills the tooth gaps and is conveyed externally around the housing into pressure area P. The hydraulic fluid is then forced out of the tooth gaps by the meshing of teeth and displaced into the lines. Fluid is trapped in the gaps between the teeth between suction and pressure area. This liquid is fed to the pressure area via a groove since pressure peaks may arise owing to compression of the trapped oil, resulting in noise and damage.

66

Rotary Vane: Working Principle To hydraulic system Volume increase

To hydraulic system

From tank

Single chamber

Volume increase From tank

Double chamber 67

Piston Pump: Working Principle

Hyd sys

From tank

To hydraulic system

compression To hydraulic system

From tank compression

Radial chamber

From tank

Axial chamber 68

Pump Specification

69

Assignment 2 • Working operation for: 1. Internal Gear Pump, 2. Vane Pump and 3. Piston Pump

70

Hydraulic Actuator Chapter 5

• There are two basic types of hydraulic actuator: – Rotary actuator (motor / rotary)

– Linear actuator (cylinder)

71

Hydraulic Motor (Rotary Movement) • Hydraulic motor comes various type same as hydraulic pump. It working operation are similar. – Gear motor – Vane motor – Piston motor

72

Linear Actuator (Linear Movement) • There are two basic types of hydraulic cylinder – single-acting and – double-acting cylinders.

Single Acting Cylinder

Double Acting Cylinder 73

Type of Linear Actuator

74

Type of Linear Actuator

75

Distribution Valve Chapter 6

Introduction •

Directional control valves are components which change, open or close flow paths in hydraulic systems. They are used to control the direction of motion of power components and the manner in which these stop. Directional control valves are shown as defined in DIN ISO 1219.

Type •

2/2-way valve

•

3/2-way valve

•

4/2-way valve

•

5/2-way valve

•

4/3-way valve

76

Symbols for directional control valves • • • • • •

The following rules apply to the representation of directional control valves: Each different switching position is shown by a square. Flow directions are indicated by arrows. Blocked ports are shown by horizontal lines. Ports are shown in the appropriate flow direction with line arrows. Drain ports are drawn as a broken line and labeled (L) to distinguish them from control ports.

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Methods of Actuation •

The switching position of a directional control valve can be changed by various actuation methods, such as push button, pedal, lever with detent, a spring is always necessary for resetting.

78

Port Designation

79

Type of Distribution Valve

(symbol)

80

Working Principle

Release position

Press position

2/2 way valve, Normally close

81

Circuit Example

Release 2/2 WV – Cylinder Extend Pressed 2/2 WV – Cylinder Retract

82

Basic Construction of 3/2 way valve

(3/2 way valve N.C)

83


84


(4/3 way valve, mid position –pump re-circulating)

85

Basic Construction of valve

(2/2 way valve N.C)

(3/2 way valve N.C)

(4/3 way valve, mid position –pump re-circulating)

86

Conversion of Valve

87

Pressure Valve Chapter 7

Pressure valves have the task of controlling and regulating the pressure in a hydraulic system. Pressure relief valves The pressure in a system is set and restricted by these valves. The control pressure is sensed at the input (P) of the valve.

Pressure regulator These valves reduce the output pressure where there is a varying higher input pressure. The control pressure is sensed at the output of the valve.

Symbol Pressure relief valves

2 way pressure regulator

3 way pressure regulator

88

Working Principle (pressure relief valve)

89

Working Principle (2 way pressure regulator)

90

Working Principle (3 way pressure regulator)

91

Basic Construction Pressure Relief Valve

2 Way Pressure Regulator

3 Way Pressure Regulator

92

Flow Valve Chapter 8

Introduction Flow control valves are used to reduce the speed of a cylinder or a motor.

Type of control valve: 1. One Way Flow Control Valve - Restrict one direction of flow only.

2. Throttle Valve (two way flow control valve) - Restrict both direction of flow.

93

Working Principle One-way flow control valve –

The one-way flow control valve where the restrictor is only effective in one direction is a combination of a restrictor and a non-return valve. The restrictor controls the flow rate in a single direction dependent on flow. In the opposite direction, the full cross-sectional flow is released and the return flow is at full pump delivery. This enables the one-way flow control valve to operate.

Control

Not control 94

Circuit Example (One way flow control valve) Extend slow

Fluid is block by check valve

Fluid enter cylinder with normal flow

Fluid have to flow through throttle valve

95

Circuit Example (One way flow control valve) Retract slow

Fluid enter cylinder with normal flow

Fluid have to flow through throttle valve

Fluid is block by check valve

96

Working Principle Throttle Valve – Flow control valves influence the volumetric flow of the fluid in both directions.

Control flow in both direction

97

Circuit Example (Throttle valve)

Extend & Retract slow

98

Block Valve (Non Return Valve) Chapter 9

99

Check Valve • Check valves can stop the flow completely in one direction. In the opposite direction the flow is free with a minimal pressure drop due to the resistance of the valve.

Spring loaded

Spring un-loaded

100

De-lockable Valve In de-lockable valve, flow can be released in the closed position by pilot control of the valve poppet. This takes place according to the following principle: 1.

Flow is possible from A to B.

2.

Flow is blocked from B to A.

3.

In order permits flow from B to A, signal X is produce.

101

Circuit Example (De-Lockable valve)

Uses when cylinder is vertically install Signal x must be connected to tank In order to release pressure at port x.

102

Circuit Example (De-Lockable valve)

Change input To suite existing valve with practical task

103

Shuttle Valve A This shuttle valve has two inlets X and Y and one outlet A. If Hydraulic fluid is applied to the first inlet X, the valve seals the opposing inlet Y, the fluid flows from X to A. Inlet X is closed, if fluid passes from Y to A. A signal is generated at the outlet. When the Fluid flow is reversed, i.e. a cylinder or valve is exhausted, the seat remains in its previously assumed position because of the pressure conditions. This valve is also called an OR element. TRUTH TABLE

X

Y

A

0

0

0

0

1

1

1

0

1

1

1

1

X

Y

104

De-lockable Double Non-Return Valve The piloted double non-return valve operates according to the following principle: Free flow is possible either in the flow direction from A1 to B1 or from A2 to B2, flow is blocked either from B1 to A1 or from B2 to A2.

If flow passes through the valve from A1 to B1, the control piston is shifted to the right and the valve poppet is lifted from its seat. By these means, flow is opened from B2 to A2 (the valve operates in a corresponding manner where there is flow from A2 to B2).

105

Circuit example

106

Malaysian Spanish Institute

Electro-Hydraulic System Chapter 10

107

Schematic Design Of An Electro-Hydraulic System

108

Electro-Hydraulic Overview Relay, Timer, Solenoid

From electro

Cylinder

Pushbutton Pushbutton

Power Supply

Hydraulic Pump

109

Electro Hydraulic Automatons Switching control

Electrical actuation

Manual actuation

110

Content of Electro-Hydraulic •

Safety precaution

•

Introduction

•

Advantages

•

Comparison

•

Electrical Fundamental

•

Electrical Input Element

•

Sensor

•

Relay

•

Solenoid

•

Electrical Timer

•

Sequence Control

111

Safety Precaution 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Pneumatic safety must be apply DO NOT wear sandals, wear covered shoes DO NOT wear excessive jewelry DO NOT wear swing-loose-long hair style, neatly tie-up the long hair or place under a proper head gear. DO NOT wear shoes with heel higher than 1" (2.5 cm) DO wear lab-coat all the time DO NOT disturb people who are conducting experiments! (or any time) NO eating or drinking inside the lab. NO social gathering is allowed in the labs. The labs should not be crowded for non-working purposes. In case of spilling water on a lab bench near power points, first SWITCH OFF the electrical power before cleaning. TO INSPECT any electrical equipment, first turn the power off and ask for the instruction/help from the lab officer in charge. Any faulty equipment should be attended by trained personnel only. DO NOT do it on your own. 112

Introduction are made up of E l ec t r o -H y d r au l i c S y s t em s hydraulic and electrical components: • The movements and forces are generated by Hydraulic means (e.g. by cylinders). • Signal input and signal processing, on the other hand, are effected by Electrical and E l e c t r o n i c components (e.g. electromechanical switching elements or stored-program controls).

113

Advantages •

Electrical signals can be transmitted via cables quickly and easily and over great distances. Mechanical signal transmission (linkages, cable-pulls) or hydraulic signal transmission (tubes, pipes) are far more complex.

•

In the field of automation, signal processing is generally effected by electrical means. This enhances the options for the use of electro-hydraulic systems in automatic production operations (e.g. in a fully automatic pressing line for the manufacture of car wings).

•

Many machines require complex control procedures (e.g. plastics processing). In such cases, an electrical control is often less complex and more economical than a mechanical or hydraulic control system.

114

Comparison

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Electrical Fundamental •

The relationship between voltage, current strength and resistance is described by Ohm‘s law. Ohm‘s law states that in a circuit with constant resistance the current strength changes in proportion to the change in voltage: – if the voltage increases, the current strength also increases. – if the voltage falls, the current strength also decreases.

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Electrical power • •

In the field of mechanical engineering, power can be defined in t erms of the work performed. The faster a task is performed, the greater the required power. Power therefore means work per unit of time. In the case of a consuming device in a circuit, electrical energy is converted into kinetic energy (e.g. electrical motor), light radiation (e.g. electrical lamp) or thermal energy (e.g. electrical heater, electrical lamp). The faster the energy is converted, the greater the electrical power.

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Power Supply • A power supply unit consists of the following modules: – the mains transformer which transforms the alternating voltage of the mains supply (e.g. 220 V) into the output voltage (mostly 24 V). – a smoothed direct voltage is generated by the rectifier G and the capacitor C. – the direct voltage is then stabilized by the in-phase regulator.

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Conversion AC to DC •

Electrical controls are generally supplied with a direct current of 24V. The alternating voltage from the power supply therefore has to be stepped down to 24V and then rectified.

AC

DC

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Electrical input elements

NORMALLY OPEN CONTACT circuit is open when the push-button is in the normal positi on

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NORMALLY CLOSED CONTACT circuit is closed when the push-button is in the normal positi on

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CHANGEOVER SWITCH These contacts combine the functions of normally closed and normally open contacts in one unit.

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Circuit example Pressed S1, H will on Pressed S1, H will off

Pressed S1, H will on, Pressed S2, H will off. 123

Practical (Electrical Input Element)

Switching ON Command S1 AND S2



And Function

H1 on

S1 OR S2

Or Function



H1 on

Switching OFF Command S1 AND S2



H1 off

And Function

S1 OR S2

 H1

Or Function 124

off

Sensor –Limit switch A mechanical limit switch is an electrical switch which is activated when a machine part or a workpiece is in a certain position.

Normally open limit switch 1-4 Normally closed limit switch 1-2 125

Sensor – Pressure switch requires a pressure to activated the sensor the pressure acts on a cylinder surface (x). If the pressure exerted exceeds the spring force of the return spring, the piston moves and operates the contact set.

Normally open limit switch 1-4

Normally closed limit switch 1-2 126

Circuit Example

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Relay • •

•

•

•

•

Relays are electromagnetically actuated switches. They consist of a housing with electromagnet and movable contacts. An electromagnetic field is created when a voltage is applied to the coil of the electromagnet. This results in attraction of the movable armature to the coil core. The armature actuates the contact assembly. This contact assembly can open or close a specific number of contacts by mechanical means. If the flow of current through the coil is interrupted, a spring returns the armature to its original position.

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Concept of a Relay (Electromagnet) • An electromagnet is a type of m a g n e t in which the m a g n e t i c f i el d is produced by the flow of an electric current . The magnetic field disappears when the current ceases.

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Working Principle

Relay 1 pole

Relay 2 pole

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Example

131

Circuit Example

Direct Control

In-direct Control

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9. Solenoids •

In electro-hydraulics, valves are actuated via solenoids. It has the same concept of electromagnet. solenoid

Directional control Valve

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Circuit Example

134

Electromechanical Switching Element (Symbol)

135

Holding Element / Latching S1  H1 ON S2  H1 OFF

S1

k1

k1

S2

K1

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Electrical Timer • A timer is used to control the sequence of an event or process. •

Two type of timer 1. Delay-On Timer 2. Delay-Off Timer

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Electrical Timer The Coil with ON delay activates its associated contacts when current is applied.

S1  5sec  H1 ON S2  H1 OFF 24V

S1

K1

K1

T1

T1

H1

S2

K1

0V

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Electrical Timer The Coil with OFF delay deactivates its associated contacts when current is applied, but only after the preset delay.

S1  H1 ON S2  5sec  H1 OFF 24V

S1

K1

K1

T1

T1

H1

S2

K1

0V

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Electrical Timer Timer for Practical installation

Note: For ON Delay: Select selector to DES.

24V

S1

t

For OFF Delay: Select selector to CON.

H1

0V

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Electro Hydraulic System Hydraulic Circuit Diagram / Power Circuit / Schematic Diagram

Control Circuit Diagram / Electrical Circuit Diagram

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Basic Hydraulic System

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