Basic Hydraulic e

Service Basic Training

Hydraulics 5.905-842 02/03

Foreword

Foreword Good servicing work calls for comprehensive and practically-oriented training as well as clear and manageable documentation. For this reason, we offer regular training courses courses and further education events covering the whole product range to all service technicians. We additionally compile servicing manuals for the most important devices which serve initially as instructions and can later be used for reference purposes. We also provide regular service information bulletins reporting on product further development. The text and pictures may not be copied, duplicated or made available to third parties without the express consent of:

ALFRED KÄRCHER GmbH & Co. KUNDENDIENSTSCHULUNG Postfach 160 D-71349 Winnenden www.karcher.de

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Service Basic Training Hydraulics 02/03

Foreword

Foreword Good servicing work calls for comprehensive and practically-oriented training as well as clear and manageable documentation. For this reason, we offer regular training courses courses and further education events covering the whole product range to all service technicians. We additionally compile servicing manuals for the most important devices which serve initially as instructions and can later be used for reference purposes. We also provide regular service information bulletins reporting on product further development. The text and pictures may not be copied, duplicated or made available to third parties without the express consent of:

ALFRED KÄRCHER GmbH & Co. KUNDENDIENSTSCHULUNG Postfach 160 D-71349 Winnenden www.karcher.de

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Contents

Contents Genera Gen erall ............................. ............................................. ............................... .............................. ............................... ........................... ........... 5 Benefits/drawbacks of hydraulics/fluid technology ....................................... ................... ............................ ........ 5 Benefits ............................................................. ....................................................................................................................... .......................................................... ......... 5 Drawbacks Drawba cks ...................................................... ..................................................................................................................... .................................................................... ..... 5

Basic hydromecha hydromechanics nics ................... ............................. ................... ................... .................... ................... ................... .................... ................ ...... 6 Pressure due to fluid height ........................................................... ................................................................................................. ...................................... 6 Pressure due to outside outside forces ......................................................... ............................................................................................ ................................... 6

Basic hydromecha hydromechanics nics ................... ............................. ................... ................... .................... ................... ................... .................... ................ ...... 7 Power transmission transmission ........................................................... ............................................................................................................. .................................................. 7 Circulatory Circulatory law ...................................................... ................................................................................................................ .......................................................... ..... 7

Basic hydromecha hydromechanics nics ................... ............................. ................... ................... .................... ................... ................... .................... ................ ...... 8 Pressure loss ............................................................... .................................................................................................................. ................................................... .... 8

Structure Structure of a hydraulic hydraulic system system .................. ............................ ................... ................... .................... ................... ................... ............. ... 9 Energy - conversion ............................................................. ........................................................................................................... .............................................. 9 Energy - control ......................................................... ............................................................................................................... .......................................................... .... 9 Energy - transport................................................................................................................9 Others ............................................................. ........................................................................................................................... ..................................................................... ....... 9

Hydraulic Hydraulic circuit circuit symbols symbols .................... ............................. ................... .................... ................... ................... .................... ................... ............. 9

Hydraulic circuit symbols ........................................ ............................................................. ............................. ........ 1 0 Line types .............................................................. ..................................................................................................................... ....................................................... ..... 10 Flow paths of lines ........................................................... ............................................................................................................ ................................................... 10 Function symbols.................................................................. symbols.... ........................................................................................................... ............................................. 10 Drive motors ............................................................... ................................................................................................................... ....................................................... ... 11 Hydraulic pumps .......................................................... ................................................................................................................ ...................................................... 11 Hydraulic cylinders ........................................................ ............................................................................................................ .................................................... 11 Possible combinations combinations ............................................................ ....................................................................................................... ........................................... 12 Flow possibilities possibilities ..................................................... ............................................................................................................. ........................................................ ... 12 Switching possibilities possibilities ............................................................. ........................................................................................................ ........................................... 12 Directional Directional valves – example ....................................................... ............................................................................................. ...................................... 13 Flow rate valves........................................................................ valves......... ...................................................................................................... ......................................... .. 13 Non-return valves ...................................................... .............................................................................................................. ........................................................ 14 Twin non-return valves ........................................................... ....................................................................................................... ............................................ 14 Pressure control valve ............................................................... ....................................................................................................... ........................................ 14 Pressure control control valve – non-return valve valve / flow control valve – non-return non-return valve ............ 15 Blower fan / impeller impeller fan .......................................................... ..................................................................................................... ........................................... 15 Oil tanks.............................................................................................................................15 Oil filter / oil cooler..............................................................................................................16 Oil tank and components components ....................................................... ................................................................................................... ............................................ 16 Function of an oil tank .............................................................. ........................................................................................................ .......................................... 16 Tasks of an oil tank ............................................................ ........................................................................................................... ................................................. 16

Routing of hydraulic hoses ......................................... .............................................................. ......................... .... 1 8


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Contents

Structure of a hydraulic plan ................................................................ 20 Basic hydraulic plan ........................................................................................................... 20 Electric motor ..................................................................................................................... 20 Pressure control valve ....................................................................................................... 21 4/3 directional valve ........................................................................................................... 21 Flow rate valve...................................................................................................................22 Oil filter ..................................................................................................................... .......... 22 Safety valve for oil filter ...................................................................................................... 23 4/3 directional valve in neutral position .............................................................................. 23 Pipe break valve ............................................................................................................... . 24

Functional sequence hydraulic plan ................................................... 25 Example KMR 1250 .................................................................................................25 Hydraulic plan pressureless condition ............................................................................... 25 Raising the debris container .............................................................................................. 26 Electric circuit diagram ...................................................................................................... 26 Hydraulic plan ................................................................................................................. ... 26 Tilting out the debris container ........................................................................................... 27 Electric circuit diagram ...................................................................................................... 27 Hydraulic plan ................................................................................................................. ... 27 Tilting back the debris container ........................................................................................ 28 Electric circuit diagram ...................................................................................................... 28 Hydraulic plan ................................................................................................................. ... 28 Lowering the debris container ............................................................................................ 29 Electric circuit diagram ...................................................................................................... 29 Hydraulic plan ................................................................................................................. ... 29

Servicing work on hydraulic systems ................................................. 30 Safety and maintenance instructions.................................................................... 30

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Basics

General

Benefits/drawbacks of hydraulics/fluid technology

The terms hydraulics or fluid technology are used to describe all drive, control and regulating components of a device in which power is generated and transmitted by pressure in a fluid. With the aid of electrical devices, hydraulics/ fluid technology can be used to achieve a high degree of positioning and velocity accuracy. In order to engender greater understanding of hydraulics/fluid technology, this basic training program will initially provide an explanation of fundamental hydromechanical principles. Primarily, this basic training program will be explaining the hydraulic circuit symbols which represent the components currently used in our devices. In addition, two examples will be used to explain the technical structure of the individual components and the sequence of a hydraulic plan.

Benefits - Space and weight-saving components capable of transmitting high forces - Fast, precise and steplessly adjustable cylinder and motor speeds - Simple overload prevention by pressure limitation - Function at full load is possible from standstill - Suitable for fast and also extremely slow, controllable movement sequences

Drawbacks - Temperature dependence of the hydraulic oil - Loss due to leakage oil - Friction loss which converts into heat and raises the temperature of the system - Vibration and noise creation tendency

This basic training program encompasses also certain laws of physics, for example of - Mass, force - Work, energy, output - Velocity, acceleration


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Basics

Basic hydromechanics Hydromechanics is the science of the physical characteristics and behaviour of fluids in a static (hydrostatics) and dynamic (hydrokinetics) status.

Pressure due to fluid height

h

p1

A1

F1

p2

A2

F2

p3

A3

If the pressure (p1 = p2 = p3) acts on surfaces of equal size (A1 = A2 = A3), the resulting forces are equally high (F1 = F2 = F3). Here, the shape of the vessel is of no significance, only the height of the fluid (h) determines the extent of the pressure.

F3

Pressure due to fluid height

Pressure due to outside forces

F A

The effect of a force (F) on a static fluid spreads evenly in all directions within the fluid. The level of the pressure (p) in the fluid is equal to the force due to weight (F) relative to the surface upon which it acts (A). The pressure (p) always acts vertically on the adjoining surfaces of the tank.

p

Pressure due to outside forces

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Basics

Basic hydromechanics Power transmission

1

S2

F1

F2

As the pressure spreads evenly to all sides, the shape of the tank is of no significance. If force (F1) acts on surface (A1), pressure (p) is created. p = F1 / A1 Pressure (p) acts on every point of the system, i.e. also on surface (A2). The achievable force (F2) (synonymous with a load to be lifted) is F2 = p x A2 If it is possible using force (F1) and surface (A1) to achieve the pressure needed to overcome the load (F2) (above surface (A2)), then the load (F2) can be lifted. (Leaving friction loss out of account). The paths (S1) and (S2) of the two pistons perform the reverse action to the surfaces (A1) and (A2). S1 / S2 = A1 / A2 Therefore S1 x A1 = S2 x A2

2

S1 p

A1

A2

Power transmission

Circulatory law

A1 A2 Q2

Q1 v2 v1

Circulatory law


The same volume of fluid flows in the same period of time through a pipe with differing cross-sections. This means that the flow rate of the fluid in the smaller cross-section must increase. The volumetric flow (Q) corresponds to the product of the cross-sectional surface of pipe (A) times the velocity of the fluid (v) Q=Axv The volumetric flow (Q) is the same at all points of the pipe. Q1 = Q2 The two cross-sections (A1) and (A2) of the pipe behave in opposition to the velocities of the fluids (v1) and (v2). A1 x v1 = A2 x v2

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Basics

Basic hydromechanics Pressure loss

p2

p3

p4

p1

8

p6

p7 ∆p

Pressure loss

p5

= p1 - p7

In order to explain these physical laws, we assumed that no friction or pressure loss occurs. Hydraulic energy cannot be transmitted through pipes without loss. Due to friction on the pipe walls or due to a restriction of the cross-section (flow control valve), hydraulic energy is transformed into heat. For hydraulically operated systems, the loss of hydraulic energy created in this way means a loss of pressure and a reduction of the flow rate. Pressure loss is represented by the symbol Dp. Its extent depends primarily upon: - The line length - The cross-section of the pipe - Surface roughness of the pipe wall - Number of bends in the pipe - Flow rate - Fluid velocity


Basics

Structure of a hydraulic system

Hydraulic circuit symbols

In hydraulic systems, mechanical energy is converted into hydraulic energy, transported in this form and controlled or regulated, then converted back into mechanical energy again.

To illustrate hydraulic correlations in accordance with DIN ISO 1219, nowadays in the majority of cases hydraulic circuit diagrams with standardized circuit symbols are used. The circuit symbols are neither to scale, nor do they claim to correspond to the actual position of the component in question. They are intended only to indicate a function. The components of a hydraulic plan are arranged from bottom to top in the direction of the energy flow: - Energy source: bottom left - Control elements in progressive sequence: upwards, from left to right - Drive systems: at the top from left to right A hydraulic circuit diagram is interpreted in a similar way to an electrical circuit diagram, the difference here being that actually visible fluid currents and pressures act as well as mechanical components. Hydraulic components are shown in the starting position of the system with pressure applied. Elements or assemblies of the same type should be indicated at the same height within a hydraulic plan. The following breakdown of circuit symbols makes no claim to completeness, and contains only the most commonly used symbols. It is intended as a tool to understanding a hydraulic circuit plan.

Energy - conversion To convert energy, on the primary side pumps are used, and on the secondary side cylinders and motors.

Energy - control The extent of the hydraulic energy and the direction in which it acts, and thus also the transmitted output are influenced in the form of pressure and volumetric flow by variable displacement pumps and by control and regulating valves.

Energy - transport The pressure fluid which is guided through pipes, hoses and holes in control blocks or control plates, assumes the function of energy transport or also only of pressure conduction.

Others A series of supplementary devices such as tanks, filters, coolers, heating elements, measuring and test units are required for storage and maintenance of the pressure fluid.


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Hydraulic circuit symbols Line types 1

1 2

2

3

Working line (continuous line = delivery or pressure line) Control line (dash line = to actuate valves or other components) Dot and dash lines = used to draw a frame around an assembly

3

Line types

Flow paths of lines

1

1 2 3

Line connections Line crossing points Flexible lines

2

3

Flow paths of lines

Function symbols 1

1 2 3 4

Direction of volumetric flow Current direction of flow Sense of rotation Adjustment facility

2

3

4

Function symbols

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Hydraulic circuit symbols Drive motors 1

1 M

2

3 2

M

Electric motor, drive shaft turns in two directions Combustion engine, two cylinders (no. of squares on the motor) drive shaft turns in two directions Hydraulic motor, two volumetric flow directions, drive shaft turns in two directions

3

Drive motors

Hydraulic pumps 1

1 2 3

One volumetric flow direction, drive shaft turns in one direction Two volumetric flow directions, drive shaft turns in one direction Two adjustable volumetric flow directions, drive shaft turns in one direction

2

3

Hydraulic pumps

Hydraulic cylinders 1 1

2

Single-acting cylinder with piston rod on one side (retraction stroke powered by integrated spring) Double-acting cylinder with piston rod on one side

2

Hydraulic cylinders


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Hydraulic circuit symbols Possible combinations 1 1

2

Directional valve with two switching positions Directional valve with three switching position

2

Possible combinations

Flow possibilities 1 1

2 3

Flow possibilities for one switching position with two connections Flow possibilities for one switching position with three connections Flow possibilities for one switching position with four connections

2

3

Flow possibilities

Switching possibilities

1

2

3

4

1 2 3 4

Actuation by electric solenoid valve Actuation by spring Actuated hydraulically Actuation by lever

Switching possibilities

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Hydraulic circuit symbols Directional valves – example

1

a

o

b

A

B

P

T

2

1

3

4/3 directional valve 4 = number of connections 3 = number of switching positions A Connections for consumers B Connections for consumers P Pressure connection (pump) T Return line connection a Switch position (left) o Switch position (idle position) b Switch position (right) 1 Compression springs for switching position (o) 2 Solenoid valve for switch position (a) 3 Solenoid valve for switch position (b)

Directional valves - example

If solenoid valve (2) is energized, switch position (a) applies. If solenoid valve (3) is energized, switch position (b) applies. In the idle position, the valve is moved to the central switch position (o) by the two compression springs (1).

Flow rate valves 1

1 2 3

2

4

Flow rate valve not adjustable (reduces the pressure and the flow rate) Flow rate valve adjustable (reduces the pressure and the flow rate) Flow control valve with regulation output current (reduces pressure and flow rate) Flow control valve with regulation output flow and relief opening (reduces pressure and flow rate)

3

4

Flow rate valves


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Hydraulic circuit symbols Non-return valves 1

1

2

2

3 3

4 5

4

6 5

6

Stop valve (manual interruption of the delivery line. Stop valve is either completely open or closed). Non-return valve, unloaded (Flow only possible in one direction) Non-return valve, spring-loaded (Flow only possible in one direction) Shuttle valve (volumetric flow can flow downwards from the left or right) Pipe break valve (in case of high pressure drop, the ball presses against the spring and prevents return flow) Pipe break valve (in the operating mode, the integrated control line does not press the non-return ball into its seat, allowing oil to flow. An integrated flow rate valve prevents the non-return ball from being pressed into its seat during return flow. In case of a high pressure drop, the ball presses into the seat and prevents return flow.

Non-return valves

Twin non-return valves A2

B2

A

B

A1

A twin non-return valve is used to move a hydraulic cylinder or to block it in an unpressurized condition. Non-return valve (A) opens when the volumetric flow runs from (A1) to (A2). A control piston opens the non-return valve (B) slightly via a control line, to permit return flow from (B2) to (B1). The same applies when the volumetric flow runs from (B1) to (B2). Then the control piston opens non-return valve (A).

B1

Twin non-return valve

Pressure control valve 1

2 1

2

Pressure control valve with internal control line (is intended to limit the pressure in the system) Pressure control valve with external control line (is intended to limit the pressure in the system)

Pressure control valve

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Basic Hydraulic e

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