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1、FluidPowerPumpsPurposeofpumpsEveryfluid—powersystemusesoneormorepumpstopressurizethehydraulicfluid.Thefluidunderpressure,inturn,performsworkintheoutputsectionofthefluid-powersystem.Thus,thepressurizedfluidmaybeusedtomoveapistoninacylinderortoturntheshaftofahydraulicmoto
2、rThepurposeofapumpinafluid-powersystemistopressurizethefluidsothatworkmaybeperformed.Somefluid-powersystemsuselowressures-lOOpsiorless-todowork.Wherealargeworkoutputisrequired,highpressures-lOOOpseormore-maybeused.Sowefindthateverymodernfluid-powersystemusesatleastonepi
3、mptopressurizethefluid.TypesofPumpsTheretypesofpumpsfinduseinfluid-powersystems:(1)rotary,(2)reciprocating,and(3)centrifugalpumps.Simplehydraulicsystemsmayusebutonetypeofpump.Thetrendistousepumpswiththemostsatisfactorycharacteristicsforthespecifictasksinvolved.Inmatchin
4、gthecharacteristicsofthepumptotherequirementsofthehydraulicsystem,itisnotunusualtofindtwotypesofpumpsinseries.Forexample,acentrifugalpumpmaybeusedtosuperchargeareciprocatingpump,orarotarypumpmaybeusedtosupplypressurizedoilforthecontrolsassociatedwithareversingvariable-d
5、isplacementreciprocatingpump.RotaryPumpsThesearebuiltinmanydifferentdesignsandextremelypopularinmodernfluid-powersystem.Themostcommonrotary-pumpdesignsusedtodayarespur-gear,internal-gear,generated-rotary,sliding-vane,andscrewpump.Eachtypehasadvantagesthatmakeitmostsuita
6、bleforagivenapplication.Spur-GearPumps.Thesepumpshavetwomatinggearsareturnedinacloselyfittedcasing.Rotationofonegear,thedriver,causesthesecond,orfollowergear,toturn.Thedrivingshaftisusuallyconnectedtotheuppergearofthepump.Whenthepumpisfirststarted,rotationofgearsforcesa
7、iroutthecasingandintothedischargepipe.Thisremovalofairfromthepumpcasingproducesapartialvacuumonthesuctionsideofthepumpinlet.Herethefluidistrappedbetweentheteethoftheupperandlowergearsandthepumpcasing.Continuedrotationofthegearsforcesthefluidoutofpumpdischarge.Pressureri
8、seinaspur-gearpumpisproducedbythesqueezingactiononthefluidasitisexpelledfrombetweenthemeshinggearteethandcasin