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1、Unit3HydraulicPowerDevicesThefunctionsofahydraulicpowerdevicearetoprovidehydraulicfluidunderpressuretoahydraulicsystemandtoprovideaplaceforstoringtheoilthatisnotinuse.Theamountoffluiddelivereddependsonthecapacityofthepump.Theamountoffluiddelivereddependsonth
2、ecapacityofthepump.Thecapacityofthepumpdependsonthefluiddisplacementperrevolutionofthepumpmultipliedbythespeedatwhichthepumpistobeoperated.Pumpmultipliedbythespeedatwhichthepumpistobeoperated.Pumpcapacityisusuallymeasuredingallonsperminute.Theheartofthepower
3、deviceisthehydraulicpump.Othercomponentsofthepowerunitincludetheoilreservoir,intakefilter,pressuregauge,pressurereliefvalve,couplingforconnectingthepumpandthedrivingmeans,whichmaybeanelectricmotor,aninternalpiping.Manypowerdevicesareequippedwithaftercoolers,
4、heatexchangers,orheaters.THEHYDRAULICPUMPThepumpcreatesapartialvacuum(pressurebelowatmospheric)ontheintakesideastheinternalmechanismstartsthoughitscycle;thentheatmosphericpressureactingontheoilinthereservoirforcestheoilintothepump,asthecycleprogresses,trapst
5、hisoil,andforcesitthroughtheoutletunderpressure.Itshouldberememberedthatthedistancethefluidcanberaisedverticallydependsontheatmosphericpressureactingonthesurfaceofthefluidandtheamountofvacuumcreatedwithinthepump.Theatmosphericpressurevarieswiththealtitude;at
6、sealevelitiscommonlytakenas14.7phis,andthetheoreticalHYDRAULICPOWERDEVICESMaximumliftatthispointisabout34feet.Thetheoreticalliftandtheactualdistancewhichafluidcanberaisedmayvarygreatly,asmechanicalimperfectionsinthepump,pipefriction,andwearofthepumppartsshou
7、ldbetakenintoconsideration.Althoughthepumpcanraisethefluidonlyatheoreticalmaximumofabout34feet,itcanforcetheliquidtomuchgreaterheights,dependingontheforceexertedonthefluid.Generally,therequirementforraisingtheliquidintothepumpamountstoamaximumdistanceofafewf
8、eet.Moststoragetanks(orreservoirs,astheyarecommonlytermedinhydraulics)havethepumpmountedontopofthetank,andtheoilhastoberaisedonlyashortdistance.Pumpsmaybedividedintotwogeneralclassifications-the
