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1、Unit3HydraulicPowerDevicesThefunctionsofahydraulicpowerdevicearetoprovidehydraulicfluidunderpressuretoahydraulicsystemandtoprovideaplaceforstoringtheoilthatisnotinuse・Theamountoffluiddelivereddependsonthecapacityofthepump・Theamountoffluiddelivereddependsonthecapacityofthepump.Theca
2、pacityofthepumpdependsonthefluiddisplacementperrevolutionofthepumpmultipliedbythespeedatwhichthepumpistobeoperated.Pumpmultipliedbythespeedatwhichthepumpistobeoperated.Pumpcapacityisusuallymeasuredingallonsperminute.Theheartofthepowerdeviceisthehydraulicpump・componentsofthepoweruni
3、tincludetheoilreservoir,intakefilter,pressuregauge,pressurereliefvalve,couplingforconnectingthepumpandthedrivingmeans,whichmaybeanelectricmotor,aninternalpiping.Manypowerdevicesareequippedwithaftercoolers,heatexchangers,orheaters・THEHYDRAULICPUMPThepumpcreatesapartialvacuum(pressur
4、ebelowatmospheric)ontheintakesideastheinternalmechanismstartsthoughitscycle;thentheatmosphericpressureactingontheoilinthereservoirforcestheoilintothepump,asthecycleprogresses,trapsthisoil,andforcesitthroughtheoutletunderpressure・Itshouldberememberedthatthedistancethefluidcanberaise
5、dverticallydependsontheatmosphericpressureactingonthesurfaceofthefluidandtheamountofvacuumcreatedwithinthepump.Theatmosphericpressurevarieswiththealtitude;atsealevelitiscommonlytakenas14.7phis,andthetheoreticalHYDRAULICPOWERDEVICESMaximumliftatthispointisabout34feet.Thetheoreticall
6、iftandtheactualdistancewhichafluidcanberaisedmayvarygreatly,asmechanicalimperfectionsinthepump,pipefriction,andwearofthepumppartsshouldbetakenintoconsideration.Althoughthepumpcanraisethefluidonlyatheoreticalmaximumofabout34feet,itcanforcetheliquidtomuchgreaterheights,dependingonthe
7、forceexertedonthefluid.Generally,therequirementforraisingtheliquidintothepumpamountstoamaximumdistanceofafewfeet.Moststoragetanks(orreservoirs,astheyarccommonlytermedinhydraulics)havethepumpmountedontopofthetank,andtheoilhastoberaisedonlyashortdistance・Pumpsmaybedividedintotwogener
8、alclassifications-theconst
