logical troubleshooting in hydraulic systems
DESCRIPTION
Logical Troubleshooting in Hydraulic SystemsTRANSCRIPT
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LogicalTroubleshooting
in HydraulicSystems
Vickers®
General Product Support
2
Index
Introduction 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shutting Down Machines 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Line Service 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking Faults 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instrumentation Principles and Measuring Instruments 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measuring instruments 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Gauges 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Gauge Installation 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flow Meters 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flow Meter Installation 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Machine malfunction procedure 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Machine faults 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System faults 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System malfunction 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System faults 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit Fault Preliminary Check 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Excessive Temperature 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Excessive Noise 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Excessive Vibration 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Excessive Leakage 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for gear and vane pumps 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for piston pumps 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for pressure relief valves 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for sequence valves 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for pressure reducing valves 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for flow control valves 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for directional control valves 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for pilot operated check valves 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for cylinders 26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for hydraulic motors 27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for accumulators 28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for coolers 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for air leaks 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System test for fluid contamination 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pump cavitation 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aeration of fluid 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Re-start procedure 34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bar trimming machine – Troubleshooting exercise 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bar trimming machine layout 36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Circuit diagram for bar trimming machine 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
“Logical Troubleshooting in Hydraulic Systems” is intended as a guide to systematic faultfindings in a hydraulic system. Vickers systems (to the extent permitted by law) accept noliability for loss or damage suffered as a result of the use of this guide. If in doubt, alwaysrefer to the original equipment manufacturer. Refer at all times to the “safety procedure” onpages 3 and 34.
Warning
3
IntroductionIt would be a virtually impossible task totry to document the cause and remedyof every possible fault that could occuron even the simplest hydraulic system.For this reason it is necessary to adopta logical approach to troubleshooting, inorder to locate a fault as quickly andaccurately as possible. Down time onmodern production machinery is veryexpensive, so an hour saved in locatinga problem may make hundreds, orsometimes thousands, of pounds worthof saving in lost production.
Inevitably, hydraulic systems arebecoming more and more complex asmethods of controlling machines becomeincreasingly sophisticated. The last tenyears has seen rapid technologicaladvances in the components used inmany hydraulic systems, and it is vital thatequipment, or machine manufacturer’sservice information or software’ keepspace with the actual hardware beingused.
It is probably true to say that there is still ageneral lack of understanding of hydraulicsin some areas of industry, and in reality,the job of a hydraulic maintenance engi-neer is now a specialized occupation withmany similarities to that of an instrument orelectrical engineer.
The object of this book is to provide pro-cedure for a logical approach to trouble-shooting, which can be extended whennecessary to cover specific machines inall areas of industry. The fundamentalsaround which this procedure is devel-oped, that is, the control of flow,pressure and direction of flow, appliesequally as well to a rolling mill in a steel-works or a winch drive on a trawler.
The Hit and Miss ApproachThe only alternative to a logical trouble-shooting method is the ‘hit and miss’approach, where units are changed atrandom until the failed component islocated. Eventually the problem may befound, but on all but the simplest ofsystems this method proves to beexpensive in terms of time and money. Itis usually the case that a large numberof perfectly servicable units are changedbefore the right one is found.
As with all troubleshooting techniques,knowledge of components and theirfunction in a system is vitally important.It is probably fair to say that when all thecomponents of a hydraulic system havebeen identified, their function deter-mined and the operation of the systemas a whole understood, the trouble-shooter has gone 51% of the waytowards finding the problem. It is impor-tant therefore, that to make use of thisbook effectively, a good understandingof the basic principles of hydraulicstogether with a knowledge of the opera-tion and application of hydraulic compo-nents should first be obtained.
Shutting Down MachinesWhenever servicing work is carried outon a hydraulic system, the overridingconsideration should be one of safety; tothe maintenance engineer himself, hiscolleagues and the machine operators.Although safe working practices relylargely on common sense, it is veryeasy to overlook a potential hazard inthe stress of a breakdown situation.Maintenance personnel should thereforediscipline themselves to go through aset procedure before commencing anywork on a hydraulic system. Becausehydraulic fluid is only slightlycompressible when compared with gas,only a relatively small amount ofexpansion has to take place to releasethe static pressure. However, wherecompressed gas can be present in ahydraulic system, either throughineffective bleeding, or where an
accumulator is fitted, extra care must betaken to release the pressure gradually.
Safety procedure for shuttingdown machines
Lower ormechanically secureall suspended loads
�Exhaust any
pressure locked inthe system
�
Drain down allaccumulators
�Discharge
both ends ofintensifier
�Isolate the
electrical controlsystem�
Isolate theelectrical power
supply
Line ServiceWhen adopting service or trouble-shooting procedures, it is useful todefine three distinct areas similar tothose used in the armed forces, that is,first, second and third line service.
First LineService or troubleshooting carried outon the machine itself and resulting in thefailed component being identified andrepaired whilst still in situs, or replaced.
Second LineInvestigation and repair of a failed orsuspect component away from themachine, possibly in a user’s ownworkshop
Third LineInvestigation, overhaul and retest of acomponent carried out at the maker’sfactory or service depot.
It should be the responsibility of themaintenance manager to decide wherethe dividing line is drawn between eacharea for his particular equipment.
4
First Line ServiceRepairon site.
Second Line ServiceRepair inworkshop.
Third Line ServiceManufacturers repair service
For example, if a pump fails on a systemit may be possible to repair the unitwhilst still on the machine i.e. first lineservice. In another case it may benecessary to replace the unit with a newone sending the failed pump to a work-shop or second line area where adecision can be made either to repair,return to manufacturer (third line) or ifthe unit has reached the end of its use-ful life, to scrap it. Obviously severalfactors will affect this decision, such asspares availability, time factors, etc.Wherever the line is drawn, the proce-dure should be clearly defined for thebenefit of maintenance personnel.
This book is confined to the first linearea i.e. working from a fault to thefailed component. Second line serviceinformation can be found in otherVickers publications together withdetails of specialist test equipment.
Checking FaultsThe troubleshooting procedure in thisbook will endeavor to answer the follow-ing questions:
What do I check?
Where do I check?
What do Icheck with?
What do I expectto read?
What do I check?Which things can be measured in ahydraulic system that will indicate wherethe problem lies? A doctor will very oftencheck a patient’s heartbeat andtemperature when making a diagnosis,to what do these correspond in ahydraulic system?
What do I check with?Knowing what to check, it is thennecessary to determine any specialinstruments or equipment that will berequired (corresponding to the doctor’sstethoscope and thermometer).
Where do I check?Whereabouts in a hydraulic system is itnecessary to carry out the checks andwhich should be done first? Asmentioned, a doctor will very oftencheck a patient’s heartbeat i.e. thehuman pump; should the hydraulicpump be check first?
What do I expect to read?Having taken a measurement at acertain point in a system, it is obviouslynecessary to know what the correctreading should be in order to drawconclusions if the reading is anydifferent from normal. Again, a doctorknows that the body temperature shouldbe 37�C so if there is any variation, adiagnosis can be made.
What do I check?A hydraulic system is a means oftransmitting and controlling power.Mechanical power is a function of forcemultiplied by distance moved persecond or force � velocity. If a hydraulicactuator is considered as a device toconvert hydraulic power to mechanicalpower, then the force (or torque) exertedby the actuator is governed by theapplied pressure and the velocity (orangular velocity) is governed by the flowrate. It follows, therefore, that flow andpressure are two basic elements of ahydraulic system that control the poweroutput. In engineering terms, velocityusually implies both speed anddirection, speed, as discussed beingcontrolled by flow rate and the directionof the actuator movement beingcontrolled by the direction of flow.
5
The three factors therefore that transmitand control power in a hydraulic systemare:
FlowPressure
and Direction of flowand it follows that in order to assess theperformance of a hydraulic system oneor more of these factors will have to bechecked. In order to decide which, it isnecessary to obtain the full facts of theproblem.
Very often when a problem is reportedon a machine, it is described in vagueterms such as “lack of power”. Aspreviously mentioned, power is afunction of both force and velocity and itis necessary to define the problem interms of one or the other. In practice,relevant questions must be asked inorder to determine exactly what theproblem is i.e. when lack of power isreported does it mean that the actuatoris moving too slowly, or is it not givingthe required force or torque?
Having defined the problem as one ofSpeed, Force (Torque) or Direction it isnow possible to define the hydraulicproblem as one of Flow, Pressure orDirection.
Although the troubleshooting procedureis based upon checking flow, pressureand direction, there are other aspects ofa system which can be measured bothas an aid to locating a failed componentand also to determine the reasons for acomponent failure. such properties are:
– Negative pressure (vacuum),especially in the area of the pumpinlet to check for problems in thesuction line.
– Temperature,generally when one component orpart of a system is hotter than therest, it is a good indication that flowis taking place.
– Noise,when checked on a regular orroutine basis is a good indicator ofpump condition.
– Contamination level,when repeated problems occur thecleanliness of the fluid shouldalways be checked to determinethe cause of the failures.
Instrumentation Principles andMeasuring InstrumentsWhat do I check with?When an electrician checks an electricalcircuit, he usually has available a meterthat will measure electric current andvoltage. In a hydraulic system thevoltage corresponds to the pressure,and is usually measured with a pressuregauge, the current corresponds to theflow and is usually measured with a flowmeter. Although the electricians meterwill measure positive or negativevoltage, if the hydraulic engineer wishesto measure a negative pressure i.e.vacuum, then a separate instrument isrequired, namely a vacuum gauge.
Apart from the basic requirements of apressure gauge, vacuum gauge andflow meter, there are several otherinstruments that can prove useful to thehydraulic engineer i.e.:
– Pressure Transducer and Recorder.If the pressure in a system needs tobe measured to an accuracygreater than that which can beobtained with a pressure gauge, orif transient pressure peaks orshocks need to be measured, thena pressure transducer can be usedwhich produces a varying voltageaccording to the pressure applied.
– Measuring Jar and Stopwatch.For measuring very small flowssuch as leakage, a graduated jarand watch may be used. This canvery often give a more accuratereading than a flow meter workingat the bottom of its range.
– Temperature Gauge orThermometer.To measure the general systemtemperature a temperature gaugecan be immersed in the fluidreservoir (sometimes incorporatedwith the level gauge). Very often thetemperature gauge incorporates aswitch to give a warning if the fluidtemperature is too low or too high.
– Thermocouple.Temperature can be measuredlocally in a system by means of athermocouple. If one part of asystem is very much hotter than therest, it is a good indication thatpower is being wasted (such as aleakage point).
– Noise Meter.Excessive noise is again a goodindication of a fault in a systemespecially the pump. In the middle ofa noisy factory it may be difficult tojudge whether a pump is more noisythan usual, so a noise meter enablesa comparison to be made between asuspect pump and a new pump.
– Particle Counter.The condition of the system fluidfrom a contamination point of viewis obviously a major factor in the lifeand performance of a system. Intrying to determine the reasons fora component failure it may benecessary therefore to measure thecleanliness of the fluid.
Although equipment may not beavailable on site to check the fluid,such a service is offered by most ofthe major fluid suppliers and filtermanufacturers.
In an electrical circuit thecurrent and voltage acrossany component can be easilychecked when fault finding.
In a hydraulic system:
The ‘voltage’ correspondsto the pressure
and is usually measured bya pressure gauge.
The ‘current’corresponds tothe flow
and is usuallymeasured by aflow meter.
Instrumentation Principles
6
System pressure isusually measured witha pressure gauge.
For very accurate measurement ofpressure or for measuring transientpressure shocks, a pressuretransducer and recordermay be used.
Flow is usually measured by a flowmeter which can be of severaldifferent types.
For very smallflows (e.g.leakage) ameasuring jarand stopwatchmay be used.
Temperature is usuallymeasured with athermometer ortemperature gauge.
For certain applications athermocouple and electricalmeter is used tomeasuretemperature.
Noise can bemeasured with anoise meter.
Fluid contaminationcan be measured
by a particlecounter.
Measuring Instruments
Considering the two basic requirementsof pressure/vacuum gauges and flowmeters, thought should now be given onhow they are to be connected into thesystem, bearing in mind the type ofinstrument concerned.
Pressure Gauges
Pressure gauges are usually of theBourdon Tube type consisting of acurved tube attached to a pointer. Whenpressure is applied to the curved tube, ittends to straighten out, exactly as agarden hose does when the tap is turnedon. As the tube straightens, the pointer ismoved around the dial, indicating theapplied pressure. Being a delicateinstrument, it is necessary to protect thegauge as much as possible frompressure shocks in the system. Usuallysome form of snubber arrangement isfitted to the stem of the gauge, and thecomplete case may be filled withglycerine to damp down vibrations.
Pressure gauges are available in severaldifferent ranges and obviously a gaugemust be chosen to suit the expectedpressure reading (if in doubt as to whatthe pressure is likely to be, start with ahigh pressure gauge first). Most pressuregauges however tend to be moreaccurate around half scale deflection i.e.a 0 – 100 bar gauge would be mostaccurate around pressures of 50 bar.
Pressure Gauge InstallationThere are several ways of connecting apressure gauge into a system as follows:
60
Case maybe filled withglycerine toaid damping.
Bourdontube
Pressureinlet
Tube tends tostraighten
under pressurecausing pointer
to rotate.
0
10
20
30
4050
70
80
90
100
Threadedplug
Porous elementrestricts flow
Metering pin
Long, narrow,spiral passagefor flow
Restricted opening
Snubber Arrangements
ÂÂÂÂ
1. The gauge can be directly connectedinto the pipework by means of a ‘tee’piece. Obviously, the gauge will besubject to all the pressure shocks in the
system so over a period of time theaccuracy will inevitably drop off.
2. The gauge can be installed with anisolating valve so that the valve is onlyopened when a pressure reading needsto be taken and the gauge is normallyisolated from shocks in the system.
3. A venting isolation valve may also beused normally of the ‘push-to-read’ or‘twist-to-read’ type which both isolates thegauge from the system and also vents thegauge to tank when the button is released.
4. A multi-station isolating valve allowsthe pressure to be read at six differentpoints in the system using only onepressure gauge. The valve is alsousually of the push-to-read type, ventingthe gauge when the button is released.
5. Most hydraulic units are providedwith gauge points in inlet and outletports usually a screwed plug. If thesystem designer has not allowed for agauge to be permanently installed in apart of the system, it is usually possibleto connect one in without having todisturb pipework, etc., provided thegauge points can be identified.
6. Quick release, self sealing test pointscan be provided around the system (oreven connected into unit gauge points)allowing the maintenance engineer tocheck pressure in the system with aportable gauge kept in his toolbox, fittedwith the appropriate male probe. (Byconnecting the male probe to the test pointwithout a pressure gauge, they can alsobe used for bleeding air from the system.)
7
1. Pressure gaugepermanentlyinstalled in pipe-work.
2. Pressuregauge installedwith shut-offvalve.
3. Pressure gaugeinstalled withventing isolationvalve.
4. Pressuregauge installedwith multi-pointselector valve.
Pressure Gauge Installation
1
2
3 4
5
6
5. Pressure gaugeplugged into unitgauge point.
6. Pressure gaugeplugged intosystem testpoint.
Flow Meters
Flow meters are available of severaldifferent types such as the float type orturbine type. In addition, test units areavailable which combine flow meter,pressure gauge and temperature gaugein one portable unit. In practice, flowmeters are rarely connected into asystem permanently since flow setting ina system is usually accomplished bymeasuring the speed of an actuator.When it is necessary to check flow in asystem, however, careful considerationshould be given to the positioning of theflow meter in the system.
3. An electrical device will beconnected to the sensor toconvert the pulses to flow rateinformation
Flowthroughtubecausesindicatorto rise intube
Flow rateis readdirectly onscale ofindicator
Float Type
2. Sensing devicedevelops anelectrical signalevery time aturbine bladepasses
1. Flow causes turbine tospin at rate determined bythe rate of flow
Hydraulic Test UnitA hydraulic test unit combines...
Pressure gaugeTemperature gauge
Flow meter
...in one unit
BAT-TER
YCHECK
BAT-TER
YAD-JUS
T
C PM
Flow Meter InstallationFlow meters may be installed in ahydraulic system to check while themachine is operating normally (on-line)or while the machine is shut down formaintenance purposes (off-line).
On-lineFigure (A) illustrates a flow meter installedin the main flow line from the pump. Byincorporating two 3-way valves in the line,a flow meter can be connected to thesystem and the 3-way valves selected todivert flow through the meter. The meterused must obviously be capable ofwithstanding the full system pressure andflow. The meter reading will indicate theflow available to the system, but if thereading is less than specification it is notimmediately apparent whether the pumpis giving less flow than required or therelief valve is leaking a proportion of thepump flow to tank. If a problem is foundhowever, the list of possible causes hasbeen narrowed down to two units, and acheck on the tank return line from therelief valve should then confirm which ofthe two units is at fault.
Measures pumpoutput atnormal systempressureDoes not allow forrelief valveleakage
LP
HP
Monitors pumpperformanceby measuringcase leakage
(B)
(A)
8
In the case of a variable pump, the pumpoutput flow will only be that actuallyrequired by the system at any time. Agood indication of pump performancehowever, can be obtained by measuringthe internal leakage in the pump, i.e.measuring the case drain flow asindicated in Figure (B). A certain amountof case leakage is inherent on brand newpumps (caused by design clearances,lubrication drilling etc.) so it will benecessary to compare the leakageactually measured with that for a pumpwithin full specification. When measuringcase leakage it is important that it isdone under steady state conditions, ie.with the pump delivering a constantvolume. The flow meter required will onlyhave to withstand pump case pressure(normally around 0.3 bar) and very lowflows so in fact a measuring jar andstopwatch may be used. It is importanthowever that the drain line is NEVERallowed to be blocked off.
Figure (C) illustrates a typical off-linearrangement. The addition of two shutoffvalves in the system allows the systemitself to be isolated and the pump flow
Off-line
Measures pumpoutput at lowpressure
Does not allow forrelief valveleakage
Measuresflow availableat actuator
HP
LP
(C)
(D)
diverted through the flow meter. Again alow pressure meter can be used since thepump flow is measured at low pressurealthough this may not give a true indicationof the pump outlet at normal workingpressure. As mentioned previously, a flowdeficiency could be caused by low pumpoutput or relief valve leakage so a furthercheck will be required if this is the case. Itis possible to incorporate a restrictor in theflow meter line in order to developpressure, in which case of course, a highpressure meter will be required.
If the output from the pump unit provesto be satisfactory, it may be necessaryto connect flow meter into other areas ofthe system. Again the addition ofisolating valves as illustrated in Figure(D) considerably simplifies the operation.
CAUTIONWhenever a flow meter isconnected into a system, it is
vital to ensure that the pump always hasdirect access to the relief valve, and therelief valve tank line is never allowed tobe blocked off or unduly restricted.
Where do I check and what do Iexpect to read?When considering failures in a hydraulicsystem there can be two alternativestarting points namely:
� Machine Malfunction –where a fault occurs in a hydraulicsystem causing a malfunction on themachine itself ie. an actuator fails tooperate correctly.
� System Malfunction –where a fault occurs in the hydraulicsystem without necessarily affectingthe machine performance in the shortterm, eg. excessive leakage, tempera-ture etc.
The two can of course occur together.For example, a pump failure wouldresult in the machine failing to operatecorrectly and would most likely beaccompanied by an increase in noiselevel. Experience has shown that it isusually better to start at the fundamentalproblem and work through the checkingprocedure, using symptoms such asheat, noise, leakage etc, as clues.
Again, common sense must prevailwhen working through this procedure,as some symptoms may point straight tothe problem area. A fountain of oilgushing from a valve points immediatelyto the problem area, but somesymptoms may not be so obvious.When a unit leaks flow from high to low,pressure heat is usually generatedlocally in that part of the system whichmay not be immediately obvious.
Erraticmovement
Incorrectthrust
Incorrectspeed
Nomovement
Movementwhere thereshouldn’t be
Wrong direction
Wrong sequence
Step 1An actuator can fail to operatecorrectly in the following ways:
Incorrect SpeedIncorrect ThrustNo MovementMovement in the Wrong DirectionErratic MovementIncorrect SequenceCreep
Whichever fault or faults haveoccurred, the fundamental problemarea should be defined wherepossible as one of FLOW,PRESSURE or DIRECTION.
Step 2
From the circuit diagram eachcomponent in the system can beidentified and its function in thesystem determined.
Step 3
A list of units that can possibly affectthe problem area can now be drawnup. e.g. A slow actuator speed can bedefined as a problem of FLOW (eventhough this may in turn be due to lackof PRESSURE, the fundamental prob-lem area is FLOW). A list of units thatcan possibly affect flow to the actuator(including the actuator itself) is drawnup bearing in mind that, for example aleaking or wrongly adjusted relief valve(i.e. a PRESSURE control valve)could affect flow to the actuator.
Step 4
The list of units can be arranged inrough order of priority based on pastexperience and also ease of checking.
Step 6
If the preliminary check does not revealthe unit at fault, a more exhaustive teston each unit can be carried out usingadditional instrumentation but withoutany unit from the system.
Step 5
A preliminary check can now be carriedout on each unit on the list in turn tocheck such things as installation,adjustment, signals etc. and also todetermine if any unit exhibits abnormalsymptoms such as excessivetemperature, noise, vibration etc.
MACHINE MALFUNCTION
Step 8
Before restarting the machine, thoughtshould be given to both the causeand the consequence of the failure.If the failure was caused bycontaminated or over-heated fluid,then further failures can be expectedand remedial action should be taken.If a pump has broken up on a system,there is a possibility of pump debrishaving entered the system whichshould be thoroughly cleaned outbefore a new pump is fitted.
THINK ABOUT WHAT CAUSEDTHE FAILURE AND ANYCONSEQUENCES OF IT.
Step 7
The instrument checks should nowreveal the failed unit and a decisioncan be made whether to repair orreplace the unit at fault.
9
Whichever the starting point, certainquestions should be answered beforeproceeding. When a problem is reported, itis important to gather as many factstogether as possible. It could be that thesame problem occurred six months agoand is recorded somewhere on a log sheetor record card in which case a good dealof time can be saved. It should beascertained whether any recentmaintenance work or adjustments havebeen made to the system. The exactnature of the failure should be determined,was it a sudden or gradual breakdown,which parts of the machine have beenaffected and which have not? It may bedifficult always to get the complete story,but an effort should be made to gather asmuch information as possible.
The philosophy of the trouble shootingprocedure is to start at the fundamentalproblem and determine which aspects ofthe hydraulic system is at fault; flow,pressure or direction. By consulting thecircuit diagram, a list of possible causescan be drawn up. The next stage is tothen look for the obvious. It is perhapshuman nature when faced with achallenging problem to search too deeplytoo quickly, in the process overlookingwhat in hindsight appears a very obvioussolution. There are certain checks that canbe carried out on a hydraulic system usingthe human senses of sight, touch andhearing and which can be carried out veryquickly. If a rigid procedure is adoptedeach time it will ensure that no obvious orapparently trivial problem is overlooked. Inpractice very many problems will be solvedat this stage without having to resort toadditional instrumentation.
Only if this stage fails to reveal theproblem is it necessary to resort to extrapressure gauges, flow meters etc. andagain a logical approach should beadopted using the algorithm charts in thisbook.
Machine malfunction procedure
10
Machine faults
StepMachine
fault
Flow Press. Direction1
Circuitdiagram
List ofunits to bechecked
Order ofchecking
Prelim.check
ALGOtest**
Failedunit**
Think!**
2
3
4
5
6
7
8
Noise&Heat
Vibration&Leaks *
* Algo’s 0.1 to 0.5** Algo’s A to L
System malfunction
System faults
A hydraulic system may exhibitsymptoms of excessive heat, noise, vibration orleakage without necessarily affecting the machineperformance in the short term.
Whichever the problem, a preliminary check can becarried out to try and identify the problem area byusing the human senses of sight, touch and hearing.
A unit may exhibit abnormal symptoms due to aproblem elsewhere in the system eg. cavitation oraeration on a pump inlet line. In this case theFAULT, CAUSE, REMEDY (F.C.R.) charts can beused to locate the problem area.
If the problem is not identified by the preliminarycheck, then a more exhaustive check must becarried out on suspect units and a similar procedureto the ‘Machine Fault’ exercise can be carried out.
SYSTEM MALFUNCTION
VibrationNoise
Heat
Leakage
11
System faults
SystemFault
HEAT NOISE VIBRATION LEAKS
Prelim.CheckAlgo 0.2
Prelim.CheckAlgo 0.3
F.C.R.Prelim.CheckAlgo 0.4
Prelim.CheckAlgo 0.5
SystemInspection
Continue on ’Machine Fault’diagram step 3
Continue on ’Machine Fault’diagram step 3
Continue on ’Machine Fault’diagram step 3
ProblemArea
12
Unit Fault Preliminary Check
Is the unitmodel
numbercorrect?
Check orchange
unit
Is the unitinstalled
correctly?
Remedyinstallation
Is the unitadjustable?
Re-adjustunit
Is the unitadjusted
correctly?
Does theunit have
an externalsignal?
Check thesignalsource
Is the signalcorrect?
Check theunit
Does the unitrespond tothe signal?
Check theunit
Does the unitexhibit abnor-
mal symptoms?(noise, heat)
Continueon nextchart
NO
YES
YES
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
NO
NO
YES
Algo 0.1
13
Excessive Temperature
Is a coolerfitted to the
system?
Check thecooler (see
chart Algo J.2)
Is thereservoir fluid
level low?
Top up thereservoir
Is the fluidcorrect (seechart Algo
L2)?
Drain andrefill with
correct fluid
Is the heatlocal to one
unit?
Continueon chartAlgo 0.1
List all unitswith tank ordrain returns
YES
NO
NO
NO
YES
YES
YES
Algo 0.2
Excessivetemperature
NO
Continueon chartAlgo 0.1
14
Excessive Noise
Is the noiseassociated with
the pump?
Top upreservoir
Is thenoise a high
pitchedscreaming
noise?
ConsultFCR 2
Can thenoise betraced toone unit
Insert vacuumgauge in
pump inlet
Is the readingmore than 5 inHg (-0.21 bar)
Check settingsand adjustments
of all valves
YES
NO
NO
NO
YES
Algo 0.3
Excessivenoise
Is the reservoirfluid level too
low?
YES
Is there air inthe system?
YES
NO
NO
Check systemrelief valvesand repair or
replace
YES
Checkthe unit
YES
Pump iscavitatingconsultFCR 1
NO
Is thealignmentcorrect?
NO Re-alignpump/motor
YES
Removepump andexamine
15
Excessive Vibration
Is the vibrationassociated with
the pump?
Replaceor repaircoupling
Is the pipeworkadequatelysupported?
Realigndriveshafts
Is thevibration
associatedwith one unit?
Is the pumpmountingcorrect?
Is there air inthe system?
Check settingsand adjustments
of all valves
YES
NO
YES
NO
YES
Algo 0.4
Excessivevibration
Is the flexiblecoupling
unbalanced?
YES
Is the align-ment correct?
NO
NO
YES
Tighten orinstall clamps
NO
Check settingand adjustment
of unit
YES
NO
Removepump andexamine
Tighten orstrengthen
pump mounts
NO
ConsultFCR2
YES
16
Excessive Leakage
Clean downthe system
Can theleakage be
traced to oneunit?
Repair orreplace
unit
Can the leak-age be tracedto one area of
pipework?
Isolate each partof the system inturn and check
for leaks
NO
NO
Algo 0.5
Repair orreplace
pipework
Check fordamaged
cooler
YES
YES
Is a watercooler fitted tothe system?
YES
NO
Excessivevibration
17
System test for gear and vane pumps
NO
Algo A.1
Correctrotation
Is the driverotationcorrect?
Check forleakage in
system
Is there aflow fromany valvereturn line
Is theflow fromthe pumpcorrect
Check nextunit on list
Reassemblepump
correctly
Is the pumpassembledcorrectly for
rotation
Check thevacuum at the
pump inlet
Is there flowpassing downthe relief valve
tank line
Check therelief valve
Is theremotion taking
place
Check pressurewhen motionhas stopped
Is theremotion taking
place
Insert flowmeter in
pump outlet
Loadsystem
Is the systemoff-loaded
Re-adjustrelief valve
Is the reliefvalve adjusted
correctly
Is thesystem problem
lack of flowCheck nextunit on list
Check driveto pump
Is the pumpshaft rotating
Is pressurereading normal
systempressure
Is there apressure read-
ing at pumpoutlet
START
NO YES
Primepump
Is the pumpprimed
Pump iscavitating
consult FCR1
Is thevacuum more
than 5” Hg.(-0.21 bar)of mercury
Check thepump
Check therelief valve
Is their flowpassing downthe relief valve
tank line
Check thepump
NO
YES
YES
NO
YES NO
NO YES YES
YES
NO NO
NO YES YES
YES NO NO
NO YES
YES NO
NO YES
YES
YES NO NO
OUTLET
INLET
OUTLET INLET INLET OUTLET
Vane Pump Intra-Vane PumpGear Pump
INLET & OUTLET
18
System test for piston pumps
Algo A.2
Correctrotation
Is the driverotationcorrect?
Is theflow fromthe pumpcorrect
Check nextunit on list
Adjustcompensator
setting
Is the pumpcompensator
adjustedcorrectly
Is there flowfrom any valve
return line
Is there flowpassing downthe relief valve
tank line
Check therelief valve
Is theremotion taking
place
Re-adjustrelief valve
setting
Is the reliefvalve adjusted
correctly
Insert flowmeter in
pump outlet
Loadsystem
Is the systemoff-loaded
Re-adjustcompensator
setting
Is the pumpcompensator
adjustedcorrectly
Is thesystem problem
lack of flow
Check nextunit on list
Check driveto pump
Is the pumpshaft rotating
Is pressurereading normal
systempressure
Is there apressure read-
ing at pumpoutlet
NO YES
Primepump
Is the pumpprimed
Check thecase drain
flow
Is the pumpon maximum
delivery
Check therelief valve
Is there flowpassing downthe relief valve
tank line
Check thepump
NO
YES
YES
NO
YES NO NO
NO YES YES
YES
NO YES
NO YES YES
YES NO NO
NO YES
YES NO
NO
YES
YES NO
OUTLET
INLET
INLET &OUTLET
PVB 5PFB 5
PVB 10 & 15PFB 10 & 15 PVB 20 & 29
INLET &OUTLET
INLET &OUTLET
START
Check pressurewhen motionhas stopped
YES
Is theremotion taking
place
Check pressurewhen motionhas stopped
YESCheck forleakage inthe system
NO
YES NORe-adjust max.
stop and/orcompensator
setting
Is thedrain flowexcessive
YES
NO
Continued on next page
19
System test for piston pumps (cont’d)
Algo A.2
Check thevacuum at the
pump inlet
OUTLET
INLET
INLET &OUTLET
PVB 5PFB 5
PVB 10 & 15PFB 10 & 15 PVB 20 & 29
INLET &OUTLET
INLET &OUTLET
Pump iscavitating
consult FCR1
YES
NO
Continued fromprevious page
Is thevacuum more
than 5” Hg.(-0.21 bar)of mercury
Checkthe
pump
20
System test for pressure relief valves
Algo B.1
Insert pressuregauge in TP1
Continue onnext chart
YES
Is the pres-sure maxi-
mum systempressure
Checkthe relief
valve
CS-06CS-10
CG-06CG-10
TP1
TP1 TP1
Is the systemproblem lack
of flow
YES
Is there flowpassing down
relief valvetank line
YES
NO
YES
Is thesystem on
load
Is theremotion
taking place
NO
Is the reliefvalve adjusted
correctly
YES
Is there flowfrom any
valve tankreturn line
YES
Checkthe relief
valve
Load thesystem
Check pressurewhen motionhas stopped
Re-adjustrelief valve
Check forleakage inthe system
NO NO
YES
NO
NO
21
System test for sequence valves
Algo B.2
Check thepressures atTP1 and TP2
YES
Are thepressures
correct
Checknext unit
on list
RG-06 & 10
TP1
TP2
Is thesystemproblem
lack of flow
YES
Is there ex-cessive flowdown valvedrain line
YES
Is thevalve
adjustedcorrectly
Is the pilotsignal correct
YES
Is the drainline blocked
NO
Is thespool free
Shut the systemdown in a safe
condition & removevalve end caps
Re-adjustthe valve
Check thepilot signal
Check thedrain line
NO NO
NO
YES
RT-06 & 10 RCT-06 & 10 RCG-06 & 10
TP2
TP1
TP2
TP1
TP2
TP1
TP2
TP1
NO
Checkthe valve
NO
YES
Checkthe valve
NO
Checknext unit
on list
YES
22
System test for pressure reducing valves
Algo B.3
Insert pressuregauges in TP1
& TP2
YES
Is there apressurereading at
TP1
XG-06 & 10
TP1
TP2
YES
Is thepressurereadingcorrect
Is thesystem on
load
Is theremotion taking
place
YES
Is the valveadjustedcorrectly
YES
Load thesystempumps
Check forleakage inthe system
Re-adjustvalve
NO NO
NO
NO
XT-06 & 10 XCT-06 & 10 XCG-06 & 10
TP2
TP1
TP2
TP1
TP2
TP1
TP2
TP1
XGL–03
TP1
TP2
Check thegauge in
TP2
Check thepressure when
motion hasstopped
YES
Is thesystem
problem lackof flow
YES
Check nextunit on list
Is thedrain linerestricted
Check thedrain line
Is thedrain flowexcessive
YES
Check nextunit on list
Check thevalve
Check thevalve
NO
NO
NO
YESNO
NO
Is thereading equalto full system
pressure
23
System test for flow control valves
Algo C.1
Correctinstallation
YES
Is thevalve
installedcorrectly
TP1
TP2
Is the valveadjustedcorrectly
YES
Is the read-ing normal
systempressure
Is reading normalsystem
pressure
YES
Is readingnormalworkingpressure
Check forloss insystem
NO
NO
FCG-02-1000
TP2
TP1
Insertgauge at
TP1
YES
Check thevalve
Are thereadings at
TP1 and TP2the same
Insert gaugeat TP3
Valve is notcompensating.Check valve
NO
NO
A
TP3TP3
Is thesystemproblem
flow
Re-adjustvalve
Check forloss insystem
Insertgauge at
TP2
System isstalled. Checkwhen actuator
is moving
Insertgauge at
TP1
Insertgauge at
TP2
Checknext unit
on list
Does gaugeread thesame as
TP1
Checknext unit
on list
NO
YES
NO
NO YES
NO
YES
YES NO
24
System test for directional control valves
Algo D.1
Insertgauges
TP1 & TP2
Is thesystem on
load
YES
Is theremotion taking
place
Is readingfull systempressure
Loadthe
system
NO
Check pilotsupply
Check nextunit on list
Is there areadingon TP1
Operate valvemanually
P to A
Check thevalve
Wait untilmotion has
finished
Checkvalve
NO
NO
DG5S4–102
A B
P T
TP1 TP2
DG3S4
DG17S4–06TP1 TP2
TP1 TP2TP1 TP2
Is readingfull systempressure
YES
NO
Operate valvemanually
P to B
Is there areadingon TP2
Is thesystem on
load
YES
Is theremotion taking
place
Check pilotsupply
Wait untilmotion has
finished
YES
NO
NO
YES
Load thesystem
NO
YES
NO
YES
YES
25
System test for pilot operated check valves
Algo E.1
Insertgauges
TP1 & TP2
Checkthe
valve
YES
Is the systemproblemcreep
Insert gauge inpilot pressure
line
Is thepressuredifferenceexcessive
Check pres-sures with flow
passing thruthe valve
Check nextunit on list
Checkpilot
supply
TP1
TP2
TP1
TP2
Is pilot pres-sure sufficientto open valve
NO
NO
YES
4CG-06 & 10 4CT-06 & 10
TP1
TP2
Does pilot pres-sure decay whenvalve is required
to close
YES
NONO
YES Checkthe
valve
Check forrestrictionin pilot line
26
System test for cylinders
Algo G.1
YES
Fully extendcylinder to end
of stroke
Is thesystem
problem erraticmotion
Bleed airfrom cylinderbleed points
NO
TP
Double acting
TP TP
TP
Off load orrelease system
pressure at cylinder ports
Disconnectannulus
connection ofcylinder
Apply pressureto full bore end
Is oil leakingfrom annulus
conn. oncylinder
Check nextunit on list
Check thecylinder
Double acting double rod
27
System test for hydraulic motors
Algo G.2
Is pressurenormalworkingpressure
Check pressureat motorinlet port
M2-200 25M, 35M45M, 50M
MFB-**
TP
TP
TP TP TP
Check pressureat motor
outlet port
Is backpressureexcessive
Check motordrain flow
Is drain flowexcessive
Disconnectmotor couplingand rotate by
hand
Check for lossin the system
Check forrestriction inreturn line
Checkthe motor
NO YES
YES
NO
Is shaftfree
Checkthe motor
YES
Checknext unit
on list
NO
NO
YES
28
System test for accumulators
Algo J.1
Is the pre-charge
pressurecorrect
Insert test gauge ingas side of accumu-lator as manufactur-
ers instructions
TP
Stop pumpsand dischargeaccumulator
Is the pres-sure switch
settingcorrect
Charge withnitrogen to
correctpressure
Check the accu-mulator accordingto manufacturers
instructions
NO YES
NO
Is shaftfree
Re-adjustpressureswitch
YES
TP
Discharge fluid fromaccumulator and
check gas pressure
Insert pressuregauge in fluid
line
Charge accumu-lator to fluid sys-
tem pressure
Is thepressurereadingcorrect
Is the reliefvalve of com-pensator ad-
justed correctly
YES
YES
Checknext unit
on list
NO
Re-adjustrelief valve orcompensator
NO
29
System test for coolers
Algo J.2
Is the temptoo high
Check the oil tempat the outlet port
of the cooler
Is the watersupply
switched on
YES
NO
Is shaftfree
YES
Is thethermostat
adjusted
Is the water out-let temp higherthan water inlet
temp
Is the waterinlet temptoo high
NO
Is there a differ-ence between oilinlet and outlet
temps
Cooler is working.Check next unit
on list
YES
Check when oilhas reachedworking temp
Open watervalve
NO
NO
YES
Re-adjustthermostat
NO
YES
Check thecooler
NO
Check watersupply
NOIs the oilflow thru
the coolercorrect
Check forlosses in the
system
YES
YES
Check thecooler
30
System test for air leaks
Algo L.1
Check pipefittings
Continuealong the
joints
Smear eachjoint with grease
one at a time
Are fittingstight
Has thepump noise
changed
Check thepump shaft
seal
Smear withgrease
YES
NO Tighten orreplace worn
fittings
NO Has thepump noise
changed
NO
YES
The last jointwas causing
aeration
YES
Has thepump noise
changed
Check thatpump and
strainers arebelow fluid
level
NO
Remove pumpand replace
shaft and seal ifneeded
Fill tank tocorrect level
Are theybelow fluid
level
Check forporous hoses
and pipefractures
YES
YES
NO
31
System test for fluid contamination
Algo L.2
Draw off asample and
compare withfresh fluid
This oil hasoxidized
Does thesystem sam-ple appear
to be darker
Can a pop-ping soundbe heard atthe test tube
YES
NO Does thefluid appearmilky white
Allow fluidto stand
YES
The fluid iswater laden
Replace
NO Allow fluidsamples to
stand for onehour together
Set up aninclined planewith a shallow
angle
Pour both sam-ples on to theincline at thesame time
Pour a quantityinto a test tube
and heat
YES
NO
Do airbubbles
appear at thesurface
YES
The fluid isbadly
aerated consultFCR 2
This fluid ispollutedReplace
NO
Did theyboth flow atthe same
speed
The fluid isof the wrong
viscosity
NO
Fluid viscosityis correct
YES
32
Pump cavitation
FCR 1
PumpCavitation
FAULT CAUSE REMEDY
Suction strainer cloggedor too small Clean or renew
Bore of suction linetoo small Fit larger bore pipes
Too many bends insuction line
Modify pipe layout
Suction line too longReduce length or fit
larger bore pipes
Fluid too cold Heat fluid torecommended temperature
Unsuitable fluid Replace with correct fluid
Air breather blockedor too small
Clean or replace element
Local restriction in suction line e.g.partly closed valve or hose collapse
Open or modify valves,renew houses, etc.
Failure of boost pumpRepair or replace boost
pump
Pump running too fast Reduce torecommended speed
Pump mounted too highabove oil level
Modify pump installation
33
Aeration of fluid
FCR 2
Aeration offluid
FAULT CAUSE REMEDY
Reservoir fluid level low Fill to correct level
Poor reservoir design Modify design
Return line in reservoirabove fluid level
Extend return pipebelow fluid level
Unsuitable fluid Replace with correct fluid
Pump shaft seal wornor damaged Renew seals
Suction line jointsallowing entry of air Renew or tighten joints
Porous suction hose Renew hose
Improper bleeding Re-bleed system
34
Re-start procedureAlgo 0.6
Has thecause of thefailure beenremedied
Can dirt haveentered the system
by the unitfailure or during
replacement
NO
YES
Is theunit the
correct one
YES
Clean or flushthe system as
required
NO
YES
Modify orreplace withcorrect unit
Remedyinstallation
Is the unitadjustable
YES
Are all hydraulic
connectionscorrect
Have thecases of pumps
& motorsbeen filled
Have all safetyinterlocks
been removed
YES
NO
Start thesystem
YES
YES
Bleed orprime as
necessary
Removesafety
interlocks
Are all personnelaware themachine isre-starting
Sound alarmor inform allpersonnel
NO
Will the systemrequire bleeding
or priming
Carry outfurther
investigation
Adjust toa safe
condition
Fill up case
Are all electrical
connectionscorrect
Remedyinstallation
Is the unitadjusted to a safe
condition forstart-up
YES
NO
NO
NO
YES NO
YES
NO
YES
NO
NO
35
Bar trimming machine – Troubleshooting exerciseIntroductionTo illustrate the procedure described inthis book, an example will be workedthrough in detail for a typical machine asshown on page 36.
The Bar Trimming Machine consists of acarriage which is driven backwards andforwards by a hydraulic motor. Mounted onthe carriage is a traverse cylinder whichmoves a cutting torch across a metal bar.Two clamp cylinders hold the bar in placeand a semi-rotary actuator pushes the baronto a roller table at the end of the cycle.
Assume that the operator has reportedthree problems which occurredsimultaneously and prior to which themachine was operating satisfactorily.
Symptoms� The carriage drive motor is slow in
both directions.
� The traverse cylinder is slow whenextending.
� The system is running hotter than usual.
Starting PointStart at the fundamental problem, i.e. theslow movement of the carriage motor andtraverse cylinder, using the heat problemas a clue. Since two machine faults haveoccurred it is not impossible that two faultshave occurred in the hydraulic systemsimultaneously. It is more likely however,that one fault in the hydraulic system iscausing both machine faults. The logicalprocedure therefore is to look at eachmachine fault in turn and arrive at a list ofunits which may be responsible for thatparticular symptom then look for unitscommon to both lists, i.e. units which couldcause both symptoms.
Machine Fault 1.Slow speed of carriage drive motor.
Step 1. The symptom is one of speed,therefore, the problem is Flow.
Step 2. Consult the circuit diagram andidentify the units and their function.
Step 3. List the units that could affectthe flow to the carriage drive motor.
(The object of this step is to narrowdown the number of units to be checkedas much as possible. It is importanthowever not to apply too muchjudgement at this stage, since it is betterto have a long list rather than a shortone which misses out the vital unit.
It is very easy to overlook a componentwhen drawing up the list, so for mostsystems it is safest to go through theparts list numerically and consider eachunit in turn.)
Referring to the circuit diagram on page37 the following units may cause theproblem:
Unit # Comments9 A partially closed inlet valve
could starve the pump andhence the system of fluid (Un-der these circumstances thepump would probably be cavi-tating and hence noisy but asmentioned above. Do not applytoo much judgement at thisstage.)
10 A blocked inlet filter couldcause the same effect
11 Low output from the pumpwould affect the carriage drivemotor since the flow to themotor is not throttled by anyflow control valves.
13 A partially closed shut-offvalve may have the sameeffect as a low pump output.
16 A partially closed check valvewill also have the same effect.
17 A leaking relief valve againreduces the effective pumpoutput.
18 A blocked return line filter mayrestrict the exhaust flow fromthe motor. (Although a by-passis fitted, the filter may havebeen installed the wrong wayaround.)
20 It can be assumed that thepurpose of the accumulator inthis system is to supplementthe pump flow, therefore anincorrect pre-charge pressuremay affect the flow rate fromthe accumulator.
21 A partially closed isolatingvalve would tend to restrictthe flow from the accumulatorand hence to the motor.
22 A blow-down valve left openwould reduce the effectiveflow from both the accumula-tor and the pump.
30 A directional valve leaking Pto T could reduce the flow tothe carriage drive motor.
31 As above.34 An excessive leakage down
the drain line of the pressurereducing valve could againreduce the flow to the carriagedrive motor.
35 A restriction in the directionalvalve controlling the carriagedrive motor (caused by a largepiece of swarf, incomplete spoolmovement or wrongly adjustedstroke adjusters for example)could reduce the flow to themotor.
Unit # Comments36 &37
Although a leaking relief valvemay affect the flow to themotor, two faults would haveto occur to affect the speed inboth directions ie. either 36 &37 both leaking or 36 & 38leaking or 37 & 39 leaking.While this is not impossible, itis probably very much lesslikely.
40 As for 30 and 31.42 As above.48 A worn or damaged motor
having excessive drainleakage would reduce theeffective flow to the motor.
49 &50
From the solenoid energiza-tion chart it can be seen thatneither the traverse cylindernor the eject rotary actuatorare operating at the sametime as the carriage drivemotor. Therefore, a leakage ineither of these two actuatorswould not affect flow to themotor.
51 Because the clamp cylindersare held down under pressurewhen the carriage drive motoris operating (refer to solenoidenergization chart) a leakageacross the piston seals couldaffect the flow to the carriagedrive motor.
52 As above.
Machine Fault 2.Slow speed of traverse cylinder whenextending.
Step 1. Again the symptom is one ofspeed, therefore the problem is Flow.
Step 2. Consult the circuit diagram andidentify the units and their functions.
Step 3. List the units that could affectthe flow to the traverse cylinder whenextending.
Unit # Comments
9 See Machine Fault 1.
10 See Machine Fault 1.
11 See Machine Fault 1.
13 See Machine Fault 1.
16 See Machine Fault 1.
17 See Machine Fault 1.
18 See Machine Fault 1.
20 See Machine Fault 1.
21 See Machine Fault 1.
36
Unit # Comments Cont’d
22 See Machine Fault 1.
30 See Machine Fault 1.
31 See Machine Fault 1.
34 See Machine Fault 1.
35 See Machine Fault 1.
40 See Machine Fault 1.
42 See Machine Fault 1.
44 Failure of the by-pass checkvalve, i.e. jammed closed, inthe flow control valve wouldrestrict the flow to the traversecylinder when extending.
49 A leakage across the pistonseals of the traverse cylinderwould reduce the effectiveflow rate to the cylinder.
51 See Machine Fault 1.
52 See Machine Fault 1.
The units common to both lists ie.units which on their own could causeboth machine faults are as follows:
9, 10, 11, 13, 16, 17, 18, 20, 21, 22,30, 31, 34, 35, 40, 42, 51, 52
Therefore from a total of 52 units on thesystem the search has been narroweddown to 18 by doing no more than lookat the circuit diagram, highlighting theimportance of being able to identify andunderstand circuit diagrams.
Step 4. Arrange the list in order ofchecking
The order in which units are checked ispurely arbitrary and may be influencedby such things as past experience,layout of components, position ofgauges etc., however, some units willinevitably be easier to check thanothers.
� Shut-off valves can be checked veryeasily to ensure they are in the correctposition, so these may come first onthe list – 9, 13, 21, 22.
� Assuming indicators are fitted to thefilters, these can also be checkedeasily – 10, 18.
� A pressure gauge is fitted to the pumpoutlet port so the setting of the pumpcompensator and relief valve can bechecked quite readily – 11, 17.
� A pressure gauge is fitted to reducingvalve 34 so the setting of this valvecan be checked – 34.
� The clamp cylinders can be quicklychecked for abnormal symptoms – 51,52.
� The directional valves can now bechecked for any abnormal symptoms –30, 31, 35, 40, 42.
� Finally check valve 16 can be checkedfor abnormal symptoms giving thecomplete list in order as –9, 13, 21,22, 10, 18, 11, 17, 34, 51, 52, 30, 31,35, 40, 42, 16.
Step 5. Preliminary check
Before going to the trouble of fittingadditional pressure gauges, flow meters,etc., or of removing pipework, there arecertain things that can be checked withthe instrumentation already installed, orwith the human senses of sight, touch,and hearing. Unless this step is carriedout, it is very easy to overlook what inhindsight appears a very obviousproblem, i.e. look for the obvious first).
For each of the units on the list thefollowing questions should be answeredwhere applicable.Is the Unit correct? (model number)Is the unit installed correctly?Is the unit adjusted correctly?Is the external signal correct?Does the unit respond to the signal?Are there any abnormal symptoms(heat, noise, etc)?Assume that the preliminary check iscarried out for each unit up to the clampcylinder 52, which is unusually hot.
Step 6. Algotest.
Having discovered that one unit exhibitsabnormal symptoms, i.e. heat, the unitcan now be checked in more detail byreferring to the system test sheet forcylinders ie. Algo G.1. Assume thathaving removed the connection from therod end of the cylinder and pressurizedthe full bore side fluid is found to beleaking from the rod end connection,i.e. the piston seals have failed.
Bar trimming machine layout
Step 7. The failed unit has now beenlocated and a decision can be madewhether to strip the unit in situ and makea repair or replace the complete unit,removing the failed unit to the secondline service area for further examination.
Step 8. Think!
Having made the repair or replaced theunit, thought should be given to both thecause and the consequence of thefailure. Assuming the cylinder pistonseals were damaged, the followingquestions should be answered beforethe machine is restarted:What caused the seals to becomedamaged?– contamination?– heat?– wrong seals?– wrong installation? etc.
Will the failure have had any effect onthe rest of the system?– If the seal has broken up, have
particles of rubber entered the system?– Has the oil become overheated and
oxidized?– Have any valves been adjusted to
compensate for the leakage and willnow require re-adjusting, etc.
By thinking about the cause and theconsequence of the failure, the sameproblem (or a consequential one) maybe prevented at a later date.
Carriage traverse cylinder
Clamp cylinders
Carriagedrivemotor
Ejectorrotaryactuator
37
Circuit diagram for bar trimming machine
A B
P T
A B
P TP T
A B
P T
A B
P T
A B
P T
A B
1
2
3
4
5
67
8
9
10
11
12
13
14
15 1617
18
19
20
21
22
23
24
25
26
2730
31
32 33
34
35
36
37
38
3940
41
42
43
44
45
46 47
48 49
50
51 52
M
a
80 bar
Pumpset
Reservoirassembly
Manifoldblock
Accumulatorstand
Pre-charge50 bar
Manifold block
35 barPressure
Tank
51 bar
DRa DRb
DR T
b a
a b
b ab ab a
A B C D E F
G H I J
EjectorCarriage traverse
DRc
Carriage driveClampClamp
70 bar
24bar
P
a b a b a b a b a b a0 0 0 0 0 0 0 0 0 0 10 1 0 1 0 0 0 0 0 0 10 1 0 1 0 1 0 0 0 0 10 1 0 1 0 0 1 0 0 0 10 1 0 1 0 0 0 1 0 0 10 1 0 1 1 0 0 0 0 0 11 0 1 0 0 0 0 0 0 0 10 0 0 0 0 0 0 0 1 0 10 0 0 0 0 0 0 0 0 1 1
30 31 35 40 42 17ValveSol
Solenoid Chart