basic hydraulic e

7/28/2019 Basic Hydraulic e

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5.905-84202/03

Hydraulics

ServiceBasic Training


2/302 Service Basic Training Hydraulics 02/03

Foreword

Foreword

Good servicing work calls for comprehensive and practically-oriented training as well as clearand manageable documentation.

For this reason, we offer regular training courses and further education events covering thewhole product range to all service technicians.

We additionally compile servicing manuals for the most important devices which serve initiallyas 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 theexpress consent of:

ALFRED KRCHER GmbH & Co.KUNDENDIENSTSCHULUNGPostfach 160D-71349 Winnendenwww.karcher.de


3/30Service Basic Training Hydraulics 02/03 3

Contents

Contents

General ...................................................................................................... 5

Benefits/drawbacks of hydraulics/fluid technology ............................................... 5Benefits ....................................................................................................................... .........5

Drawbacks ..........................................................................................................................5

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

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

Basic hydromechanics ............................................................................................. 8Pressure loss .................................................................................................................. ....8

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

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

Hydraulic circuit symbols ..................................................................... 10Line types ..................................................................................................................... .....10

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

Routing of hydraulic hoses .................................................................. 18



Contents

Structure of a hydraulic plan ................................................................ 20Basic hydraulic plan........................................................................................................... 20Electric motor ..................................................................................................................... 20

Pressure control valve ....................................................................................................... 214/3 directional valve ...........................................................................................................21Flow rate valve...................................................................................................................22Oil filter ..................................................................................................................... .......... 22Safety valve for oil filter ...................................................................................................... 234/3 directional valve in neutral position .............................................................................. 23Pipe break valve ............................................................................................................... .24

Functional sequence hydraulic plan ................................................... 25

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

Hydraulic plan ................................................................................................................. ...29

Servicing work on hydraulic systems ................................................. 30

Safety and maintenance instructions.................................................................... 30



Basics

General

The terms hydraulics or fluid technology areused to describe all drive, control and regula-ting components of a device in which power isgenerated and transmitted by pressure in a

fluid.With the aid of electrical devices, hydraulics/fluid technology can be used to achieve a highdegree of positioning and velocity accuracy.

In order to engender greater understanding ofhydraulics/fluid technology, this basic trainingprogram will initially provide an explanation offundamental hydromechanical principles.

Primarily, this basic training program will beexplaining the hydraulic circuit symbols whichrepresent the components currently used in

our devices.In addition, two examples will be used toexplain the technical structure of the individualcomponents and the sequence of a hydraulicplan.

This basic training program encompassesalso certain laws of physics, for example of

- Mass, force

- Work, energy, output

- Velocity, acceleration

Benefits/drawbacks ofhydraulics/fluid technology

Benefits- Space and weight-saving components

capable of transmitting high forces

- Fast, precise and steplessly adjustablecylinder and motor speeds

- Simple overload prevention by pressurelimitation

- Function at full load is possible from stand-still

- 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 andraises the temperature of the system

- Vibration and noise creation tendency



Basics

p1 p2 p3h

F1 F2 F3A1 A2 A3

Pressure due to fluid height

Pressure due to outside forces

F

p

A

Basic hydromechanicsHydromechanics is the science of thephysical characteristics and behaviour of fluidsin a static (hydrostatics) and dynamic(hydrokinetics) status.

Pressure due to outside forcesThe 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 isequal to the force due to weight (F) relative tothe surface upon which it acts (A). The pres-sure (p) always acts vertically on the adjoiningsurfaces of the tank.

Pressure due to fluid heightIf the pressure (p1 = p2 = p3) acts on sur-faces of equal size (A1 = A2 = A3), theresulting forces are equally high (F1 = F2 =F3).

Here, the shape of the vessel is of nosignificance, only the height of the fluid (h)determines the extent of the pressure.



Basics

Power transmissionAs 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 thesystem, i.e. also on surface (A2). Theachievable force (F2) (synonymous with a loadto be lifted) is

F2 = p x A2

If it is possible using force (F1) and surface(A1) to achieve the pressure needed to over-come the load (F2) (above surface (A2)), thenthe load (F2) can be lifted. (Leaving frictionloss out of account).

The paths (S1) and (S2) of the two pistonsperform the reverse action to the surfaces(A1) and (A2).

S1 / S2 = A1 / A2

Therefore

S1 x A1 = S2 x A2

S1

A1 A2

S2F11 F2 2

p

Power transmission

Circulatory law

v2

v1

A2

A1

Q1 Q2

Circulatory lawThe same volume of fluid flows in the sameperiod of time through a pipe with differing

cross-sections. This means that the flow rateof the fluid in the smaller cross-section mustincrease.

The volumetric flow (Q) corresponds to theproduct of the cross-sectional surface of pipe(A) times the velocity of the fluid (v)

Q = A x v

The volumetric flow (Q) is the same at allpoints of the pipe.

Q1 = Q2

The two cross-sections (A1) and (A2) of thepipe behave in opposition to the velocities ofthe fluids (v1) and (v2).

A1 x v1 = A2 x v2

Basic hydromechanics



Basics

Pressure lossIn order to explain these physical laws, weassumed that no friction or pressure lossoccurs.

Hydraulic energy cannot be transmittedthrough pipes without loss.

Due to friction on the pipe walls or due to arestriction of the cross-section (flow controlvalve), hydraulic energy is transformed intoheat. For hydraulically operated systems, theloss of hydraulic energy created in this waymeans a loss of pressure and a reduction ofthe flow rate.

Pressure loss is represented by the symbolDp. 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

Pressure loss

Basic hydromechanics

p1

p2 p3 p4 p5 p6

p7

p = p1 - p7



Basics

Structure of a hydraulic systemIn hydraulic systems, mechanical energy isconverted into hydraulic energy, transported inthis form and controlled or regulated, thenconverted back into mechanical energy again.

Energy - conversionTo convert energy, on the primary side pumpsare used, and on the secondary side cylindersand motors.

Energy - controlThe extent of the hydraulic energy and thedirection in which it acts, and thus also thetransmitted output are influenced in the form ofpressure and volumetric flow by variabledisplacement pumps and by control and

regulating valves.

Energy - transportThe pressure fluid which is guided throughpipes, hoses and holes in control blocks orcontrol plates, assumes the function of energytransport or also only of pressure conduction.

OthersA series of supplementary devices such astanks, filters, coolers, heating elements,

measuring and test units are required forstorage and maintenance of the pressure fluid.

To illustrate hydraulic correlations inaccordance with DIN ISO 1219, nowadays inthe majority of cases hydraulic circuit dia-grams with standardized circuit symbols areused.

The circuit symbols are neither to scale, nordo they claim to correspond to the actualposition of the component in question. Theyare intended only to indicate a function.

The components of a hydraulic plan arearranged from bottom to top in the direction ofthe 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 asimilar way to an electrical circuit diagram, thedifference here being that actually visible fluidcurrents and pressures act as well asmechanical components.

Hydraulic components are shown in thestarting position of the system with pressureapplied.

Elements or assemblies of the same typeshould be indicated at the same height within ahydraulic plan.

The following breakdown of circuit symbolsmakes no claim to completeness, andcontains only the most commonly usedsymbols. It is intended as a tool tounderstanding a hydraulic circuit plan.

Hydraulic circuit symbols




1

2

3

Line types

1 Working line (continuous line = delivery orpressure line)

2 Control line (dash line = to actuate valves

or other components)3 Dot and dash lines = used to draw a

frame around an assembly

1

2

3

Flow paths of lines

1 Line connections

2 Line crossing points

3 Flexible lines

Function symbols

1 Direction of volumetric flow

2 Current direction of flow

3 Sense of rotation

4 Adjustment facility

Line types

Flow paths of lines

Function symbols

2

3

1

4





Drive motors

1 Electric motor, drive shaft turns in twodirections

2 Combustion engine, two cylinders (no. of

squares on the motor)drive shaft turns in two directions

3 Hydraulic motor,

two volumetric flow directions,

drive shaft turns in two directions

Hydraulic pumps

1 One volumetric flow direction, drive shaftturns in one direction

2 Two volumetric flow directions, drive shaftturns in one direction

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

Hydraulic cylinders

1 Single-acting cylinder with piston rod on

one side (retraction stroke powered byintegrated spring)

2 Double-acting cylinder with piston rod onone side

Drive motors

Hydraulic pumps

Hydraulic cylinders

1

2

3

M

M

1

2

3

1

2





Possible combinations

1 Directional valve with two switchingpositions

2 Directional valve with three switching

position

Flow possibilities

1 Flow possibilities for one switchingposition with two connections

2 Flow possibilities for one switchingposition with three connections

3 Flow possibilities for one switchingposition with four connections

Switching possibilities

1 Actuation by electric solenoid valve

2 Actuation by spring

3 Actuated hydraulically

4 Actuation by lever

Possible combinations

Flow possibilities

Switching possibilities

1

2

1

2

3

1 2

3 4





P

A

T

B

a1

2

o b 1

3

Directional valves example

4/3 directional valve

4 = number of connections

3 = number of switching positions

A Connections for consumersB 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 switchingposition (o)

2 Solenoid valve for switch position (a)

3 Solenoid valve for switch position (b)

If solenoid valve (2) is energized, switchposition (a) applies. If solenoid valve (3) isenergized, switch position (b) applies. In theidle position, the valve is moved to the centralswitch position (o) by the two compressionsprings (1).

Flow rate valves

1 Flow rate valve not adjustable (reduces

the pressure and the flow rate)2 Flow rate valve adjustable (reduces the

pressure and the flow rate)

3 Flow control valve with regulation outputcurrent (reduces pressure and flow rate)

4 Flow control valve with regulation outputflow and relief opening (reduces pressureand flow rate)

Directional valves - example

Flow rate valves

2

3

4

1





Non-return valves

1 Stop valve (manual interruption of thedelivery line. Stop valve is eithercompletely open or closed).

2 Non-return valve, unloaded(Flow only possible in one direction)

3 Non-return valve, spring-loaded(Flow only possible in one direction)

4 Shuttle valve (volumetric flow can flowdownwards from the left or right)

5 Pipe break valve (in case of highpressure drop, the ball presses againstthe spring and prevents return flow)

6 Pipe break valve (in the operating mode,the integrated control line does not press

the non-return ball into its seat, allowingoil to flow. An integrated flow rate valveprevents the non-return ball from beingpressed into its seat during return flow. Incase of a high pressure drop, the ballpresses into the seat and prevents returnflow.

Twin non-return valvesA twin non-return valve is used to move ahydraulic cylinder or to block it in an

unpressurized condition.Non-return valve (A) opens when thevolumetric flow runs from (A1) to (A2).

A control piston opens the non-return valve (B)slightly via a control line, to permit return flowfrom (B2) to (B1).

The same applies when the volumetric flowruns from (B1) to (B2). Then the control pistonopens non-return valve (A).

Pressure control valve

1 Pressure control valve with internalcontrol line (is intended to limit thepressure in the system)

2 Pressure control valve with externalcontrol line (is intended to limit thepressure in the system)

Non-return valves

Twin non-return valve


A B

A1

A2

B1

B2

1 2


2

4

6

3

1

5




Oil tanks

1 Oil tank

2 Oil tank (for the sake of clarity small oiltanks are additionally drawn at the endsof lines in the hydraulic plan, but what ismeant is the actual oil tank.

Blower fan / impeller fan

1 Blower fan, e.g. for ventilation, extraction,compression

2 Impeller fan, e.g. for cooling

Pressure control valve non-return valve /flow control valve non-return valve

1 Pressure control valve non-return valve(the pressure is limited in one direction,flow is free in the other direction. Springadjustable).

2 Flow control valve non-return valve(the pressure and flow rate are reduced inone direction, flow is free in the otherdirection. Throttle adjustable)

Pressure control / flow control non-retrn valves

Blower fan / impeller fan

Oil tanks

1

2

1 2

1

2





Oil filter / oil cooler

1 Oil filter (frequently arranged in the returnline)Causes of contamination in a hydraulicsystem- production, assembly- creation of abraded particles duringoperation- environment, maintenance, servicing

2 Oil cooler

1

5

2

3

4

Oil tank and components

1 Pump

2 Filter

3 Air cushion

4 Level fluctuation

5 Drainage screw

Function of an oil tankThe pump draws the oil out of the tank.

Once it has passed through the consumers,the oil flows back to the oil tank via a filter.

Tasks of an oil tank- To accommodate the entire oil volume in the

system

- To separate air by providing the greatestpossible oil surface and a long dwell periodof the oil in the tank

- It allows contamination particles not caughtin the filter to settle on the tank floor. This iswhy the tank has a sloping floor

- Separation of condensation which formsdue to temperature fluctuations in the oiltank. It collects at the deepest point of thetank, another reason why the oil tank has asloping floor.

Oil filter / oil cooler

Components of an oil tank

1 2




Routing of hydraulic hoses

Avoid kinks

Avoid kinks

Avoid kinksAvoid kinks

Never install hydraulic hoses pulled tight

Never install hydraulic hoses pulled tight


1

2

4

3 6

5




Hydraulic hoses are used as flexibleconnecting lines between hydraulic deviceswhich move in opposition to each other, orwhere spatial circumstances are unfavourablefor laying lines.

They are also used as a way of reducing noiseand vibrations.

When laying hydraulic hoses, they must neverbe twisted or installed with an excessivelylong loop.

Figs. (1) and (2) illustrate that hoses shouldnever be installed pulled tight, so as to avoidelongation and to ensure that pressure shocksare absorbed.

Figs. (3), (4), (5) and (6) illustrate that kinksmust be avoided.

As a measure to avoid abrasion of the hose,clamping clips should never be used. Hoseswhich can rub against other components mustbe provided with a protective sheathing.




Structure of a hydraulic plan

Basic hydraulic circuit diagram

Basic hydraulic planThe basic hydraulic plan consists of

1 Oil tank

2 Working line3 Pump

4 4 / 3 directional valve

5 Cylinder

Electric motorIn order to drive the pump, an electric motor isconnected upstream.

The pump now draws the oil from the oil tankand transports it to the 4 / 3 directional valve.

Electric motor


1

2

3

4

5

M





Pressure control valveIn order to prevent damage to the hydrauliccomponents through excess pressure, apressure control valve is used. If the pressureexceeds the limit, the oil is now able to flow

back into the oil tank through the pressurecontrol valve.

4 / 3 - directional valve

4/3 directional valveThe right-hand solenoid valve is energized andswitches the 4/3 directional valve to the right-hand switch position.

The oil is now able to flow through the 4/3directional valves, allowing the cylinder toextend. The oil then flows back into the oil tankfrom the unpressurized side.

With the hydraulic plan structure shown here,the cylinder has been extended in rapidtraverse, as the pressure is acting completely

on the cylinder.


M

M




Flow rate valveIf a flow rate valve is integrated, the cylinderextends more slowly. The speed at which thecylinder extends cannot be regulated by thisflow control valve, as this has been

permanently set by the manufacturer.

Flow control valve

Oil filter

Oil filterIn order to prevent damage to the hydraulicsystem due to contamination, an oil filter isintegrated into the return line.


M

M




Safety valve for oil filterIf the pressure increases in the return line dueto a contaminated oil filter, a bypass withsafety valve is used (spring loaded non-returnvalve). The hydraulic oil flows unfiltered

through this bypass valve into the oil tank.

Safety valve for oil filter

4 / 3 - directional valve in neutral position

4/3 directional valve in neutral positionIf the right-hand solenoid valve of the 4/3directional valve is de-energized, the left-handspring sets the 4/3 directional valve to theneutral position.

The oil flows back through the pressurecontrol valve. The cylinder remains extended.


M x

M




Pipe break valveThe pipe break valve prevents the cylinderfrom retracting in an uncontrolled mannerunder load (risk of accidents) in the event of adefective or burst pressure pipe.

Pipe breakage valve


M



Functional sequence hydraulic plan

M

34

5

6

7 12

11

8

109

13

14

2

1

Hydraulic circuit diagram, pressureless condition

Hydraulic plan pressureless conditionThis hydraulic plan illustrates the raising /lowering and tilting action of a debris container.

1 Oil tank2 Oil filter

3 Electric motor, hydraulic unit

4 Hydraulic pump

5 Non-return valve

6 4/2 directional valve, tilt debris container

7 2/2 directional valve, raise / lower debriscontainer

8 Pipe break valve

9 Hydraulic cylinder, raise debris container

10 Hydraulic cylinder with gas pressurespring, tilt debris container

11 Hydraulic unit

12 Flow rate valve

13 Flow control valve

14 Pressure control valve

The functions are explained step by step overthe next pages in conjunction with theelectrical circuit diagram.

Example KMR 1250




M

+

-

S5

S6

Y2

S7

Y1

S8

M2

M

34

5

6

7 12

11

8

109

13

14

2

1

Raising the debris container

Electric circuit diagramIf the two switches (S5) and (S8) are pressedtogether, the motor (M2) is switched on(build-up of hydraulic pressure).

The solenoid valves (Y2) and (Y1) are notactivated.

Switching on electric motor (M2)

Raising the debris container

Hydraulic planAs soon as the electric motor (3) is running,the pump (4) draws oil from the oil tank (1) andthrough the filter (2). The pump (4) transportsthe oil through the non-return valve (5), the 4/2directional valve (6), the 2/2 directional valve(7) and the pipe break valve (8) to the hydrauliccylinder (9). This extends and raises thedebris container.

The two switches (S5) and (S8) must remain

depressed until the hydraulic cylinder (9) hascompletely extended (two-hand safetyoperation).

Example KMR 1250




M

+

-

S5

S6

Y2

S7

Y1

S8

M2

M

34

5

6

7 12

11

8

109

13

14

2

1

Tilting out the debris container

Electric circuit diagramIf the two switches (S5) and (S7) are pressedtogether, the motor (M2) is switched on(build-up of hydraulic pressure) and thesolenoid valve (Y1) is activated at the sametime.

Activating solenoid valve (Y1)

Titing out the debris container

Hydraulic planAs soon as the solenoid valve (Y1) of the 4/2way valve (6) is activated, it switches to theleft-hand switch position. The pump (4)transports the oil to the hydraulic cylinder (10),which extends and tilts the debris container.

The two switches (S5) and (S7) must remaindepressed until the hydraulic cylinder (10) hascompletely extended (two-hand safetyoperation).

Example KMR 1250




M

+

-

S5

S6

Y2

S7

Y1

S8

M2

M

34

5

6

7 12

11

8

109

13

14

2

1

Keys in neutral position

Tilting back the debris container

Tilting back the debris container

Electric circuit diagramIf the two switches (S5) and (S7) are released,the motor (M2) is switched off (no hydraulicpressure) and the solenoid valve (Y1) is de-energized.

Hydraulic planThe 4/2 directional valve (6) is pressed backinto the right-hand switch position again by itsspring. As soon as the 4/2 directional valve (6)is in the right-hand switch position, the gaspressure spring is able to press the pistonback of the hydraulic cylinder (10). The oilflows through the flow rate valve (12), the 4/2directional valve (6) and the flow control valve(13) back into the oil tank (1).

Example KMR 1250




M

+

-

S5

S6

Y2

S7

Y1

S8

M2

M

34

5

6

7 12

11

8

109

13

14

2

1

Activating solenoid valve (Y1) and (Y2)

Lowering the debris container

Lowering the debris container

Electric circuit diagramIf the two switches (S5) and (S6) are pressedtogether, the solenoid valves (Y2) and (Y1) areactivated. The motor (M2) remains deactivated(no hydraulic pressure).

Hydraulic planAs soon as the solenoid valves (Y1, Y2) of the4/2 directional valve (6) and of the 2/2directional valve (7) are activated, the 4/2directional valve (6) switches to the left switchposition and the 2/2 directional valve (7) intothe right switch position. The net weight of thedebris container presses the oil out of thehydraulic cylinder (9), through the pipe breakvalve (8), the 2/2 directional valve (7), the 4/2directional valve (6) and the flow control valve(13) back to the oil tank (1).

The pipe break valve (8) is not quite closed bythe system pressure, allowing the oil to flowthrough at a lower velocity.

The two keys (S5) and (S6) must remaindepressed until the hydraulic cylinder (9) hascompletely retracted (two-hand safetyoperation).

Example KMR 1250


30/30

Servicing work on hydraulic systems

For safety reasons, no pipe screw unions,connections and devices may be loosened aslong as the system is pressurized. If any workhas to be performed under a raised container,this must be carefully supported and the

machine safeguarded against rolling away.

On principle, ensuring the greatest possibledegree of cleanliness during thecommissioning, repair and maintenance ofhydraulic systems, use of the correct hydraulicoil and the right operating temperature willguarantee a long service life.

- Spare parts for the hydraulic system aresupplied with closed connections. The

covers should remain in place until they areassembled with the connecting pipes.

- If delivered unflushed and closed, hosesand nipple connections should be flushedthrough with cleaning emulsion and driedwith compressed air before mounting.

- Objects used for filling (measuring cups,funnels) should be used exclusively for newoil of the same type. Prevent anycontamination due to old oil, motor oil ordust.

- We recommend taking an oil sample ofevery new device before delivery, in orderto discover the degree of newcontamination. This ensures that the qualityof workmanship is documented in the eventof any warranty disputes.

- Drained oil is generally contaminated by thecollecting container and must be filteredbefore refilling.

- If defective hydraulic components areexchanged, the system must always beflushed through (if at all possible using the

same oil type) and filled with new oil.

Safety and maintenance instructions- The water content can be verified by filling a

test tube with a sample. The water willseparate and sink to the bottom after acertain period. Cloudiness of the oil alsopoints towards a water content.

- Contamination by foreign bodies andoxidation cause the oil to turn dark in colour.The coloration can be assessed bycomparing with the original oil. It is alsopossible to verify the existence ofcontamination and oxidation by placing adrop of oil on white blotting paper. If moreprecise investigation is required, oil samplescan be sent in to the manufacturer (labora-tory testing).

- The ideal temperature of the oil is around50C. In practice, temperatures of 60-80Care quite commonplace. Remember thatworking at higher temperatures acceleratesthe ageing process of the oil.Should overheating occur, alwaysinvestigate the root cause.

basic hydraulic e

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