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FAILURE ANALYSISA Guide to Analyzing Axial PistonPump FailuresOilgear CompanyMilwaukee, USA1 PowerInnovative Fluid80-776, Rev. 4/05
Typical Failure Modes ContaminationFluid IssueOver PressurizationImproper Inlet ConditionCase To Inlet DifferentialMiscellaneous2 PowerInnovative Fluid
CONTAMINATION10 Micron,Beta 10 of 4 or BetterISO Contamination Grade of 21/19/16O PISTON SEIZED IN BORE, PULLS SHOE OFFO PISTONS SHOW FINE SCRATCHES,DULL FINISHO EXCESSIVE WEAR ON SWASHBLOCK FACE, SHOE FACE ANDVALVE PLATE FACEO EXCESSIVE WEAR ON SADDLE BEARINGSO HYDRO-DYNAMIC BEARING WORNO CONTROL UNSTABLE: PISTON STICKING, COMPENSATOR SPOOLSTUCK OR WORN, ORIFICE IN CONTROL PISTON PLUGGED3 PowerInnovative Fluid
PISTONTHATSEIZED INBORENote MetalTransfer4 PowerInnovative Fluid
VERTICAL SCRATCHES:A Clear Indication ofContamination5 PowerInnovative Fluid
DULL ANDSCRATCHYFINISHNormal Appearance:A Mirror FinishAbnormal Appearance:A Steel Wool Look6 PowerInnovative Fluid
SHOE WEARPLATESHOWINGSIGNS OF WEARDUE TO DIRTScratchy UnevenWear7 PowerInnovative Fluid
Fluid IssueViscosity too Low, Operating Temperature tooHigh, Not a Hydraulic Fluid, Fluid Breaking DownOOOOOOPISTON SEIZED IN BORE, PULLS PISTON SHOESHOE FACES AND OR VALVE PLATE FACESMEAREDBALL WORN THROUGH SHOE RETAINERSHAFT SEAL LEAKSCAVITATION, AIR ENTRAINMENTEXCESSIVE SADDLE BEARING WEAR8 PowerInnovative Fluid
VALVEPLATE RUNON A BADFLUIDNote theSmearedRunningSurface9 PowerInnovative Fluid
WORNFULCRUMBALLTypical Failure onLow LubricityFluid10 PowerInnovative Fluid
WORNSADDLEBEARINGNote theMaterial hasDelaminated11 PowerInnovative Fluid
OVER PRESSURIZATION/SPIKESSpike Relief Always RecommendedOExcessive swashblock face, cylinder to valve plate wearOPistons broken at necksOBroken shaft where cylinder ridesOBroken tail shaft (dual)OControl pin brokenOCylinder cracked between kidneysOControl O-ring, gasket failure (PVW)12 PowerInnovative Fluid
EXCESSIVEWEAR ONCYLINDERFACECracksWouldAppearBetweenKidneys13 PowerInnovative Fluid
TORSIONAL FATIGUE:Note Cone Shaped Failure14 PowerInnovative Fluid
BENDING FATIGUEFAILURENote Straight Break15 PowerInnovative Fluid
IMPROPER INLET CONDITIONSSuction Strainer not RecommendedOCAVITATION ON VALVE PLATE FACEONOISE (MARBLE SOUND)16 PowerInnovative Fluid
CAVITATION ONCOMPRESSIONBRIDGE17 PowerInnovative Fluid
CASE TO INLET DIFFERENTIALIn General Differential Cannot Exceed 10 PSIOSHOE EDGES ROUNDEDOSHOES LOOSE ON BALLSOSWASHBLOCK WEAR, HALF MOONSHAPEOEXCESSIVE WEAR ON BACK OF SHOEFLANGESOSEAL RETAINER BENT18 PowerInnovative Fluid
WHAT DOES CASEPRESSURE DO ?30 PSI AT INLET, O PSI CASE19 PowerInnovative Fluid
TROUBLE !!!!!0 PSI INLET, 30 PSI CASE20 PowerInnovative Fluid
STAGES OFDAMAGEDUE TOSHOE LIFT3rd Stage2nd Stage1st Stage21 PowerInnovative Fluid
THEFINALSTAGEOFSHOELIFT22 PowerInnovative Fluid
HALF MOON SHAPED MARKSA Sure Signof Shoe Lift23 PowerInnovative Fluid
ROLLED SHOES: THE TELLTALE OF SHOE LIFT24 PowerInnovative Fluid
WEAR ONSHOERETAINERFROMSHOEFLANGES25 PowerInnovative Fluid
BENT SEAL RETAINER26 PowerInnovative Fluid
MISCELLANEOUSOINPUT SHAFT BROKEN8MISALIGNMENT8TORQUE REVERSALOCONTROL INSTABILITY8AIR8INCREASE CONTROL PISTON ORIFICEOPUMP VIBRATES8MISALIGNMENT8COUPLING HALF'S TOUCHING27 PowerInnovative Fluid
HELPFUL HINTS FORANALYZING BASKET CASESOThe last piece to fail will have the least amount of damageOTry to piece together the broken parts. This may seem likea waste of time but many times you will observe thingswhich can help you determine the original cause of failure.OGet the history of events:8What recently changed ?8What was going on just prior to failure ?8How long was pump run ?8Talk to the operators28 PowerInnovative Fluid
KEYS TO FAILUREANALYSISODon’t go into a customers problem with apreconceived idea about the causeODon’t assume anything, verify everythingODon’t overlook the obvious29 PowerInnovative Fluid
FAILURE ANALYSIS A Guide to Analyzing Axial Piston Pump Failures Oilgear Company Milwaukee, USA 80-776, Rev. 4/05
