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1、FluidPowerPumpsPurposeofpumpsEveryfluid-powersystemusesoneormorepumpstopressurizethehydraulicfluid.Thefluidunderpressure,inturn,performsworkintheoutputsectionofthefluid-powersystem.Thus,thepressurizedfluidmaybeusedtomoveapistoninacylinderortoturntheshaftofahydrauli
2、cmotor.Thepurposeofapumpinafluid-powersystemistopressurizethefluidsothatworkmaybeperformed.Somefluid-powersystemsuselowressures-100psiorless-todowork.Wherealargeworkoutputisrequired,highpressures-1000pseormore-maybeused.Sowefindthateverymodernfluid-powersystemusesa
3、tleastonepimptopressurizethefluid.TypesofPumpsTheretypesofpumpsfinduseinfluid-powersystems:(1)rotary,(2)reciprocating,and(3)centrifugalpumps.Simplehydraulicsystemsmayusebutonetypeofpump.Thetrendistousepumpswiththemostsatisfactorycharacteristicsforthespecifictasksin
4、volved.Inmatchingthecharacteristicsofthepumptotherequirementsofthehydraulicsystem,itisnotunusualtofindtwotypesofpumpsinseries.Forexample,acentrifugalpumpmaybeusedtosuperchargeareciprocatingpump,orarotarypumpmaybeusedtosupplypressurizedoilforthecontrolsassociatedwit
5、hareversingvariable-displacementreciprocatingpump.RotaryPumpsThesearebuiltinmanydifferentdesignsandextremelypopularinmodernfluid-powersystem.Themostcommonrotary-pumpdesignsusedtodayarespur-gear,internal-gear,generated-rotary,sliding-vane,andscrewpump.Eachtypehasadv
6、antagesthatmakeitmostsuitableforagivenapplication.Spur-GearPumps.Thesepumpshavetwomatinggearsareturnedinacloselyfittedcasing.Rotationofonegear,thedriver,causesthesecond,orfollowergear,toturn.Thedrivingshaftisusuallyconnectedtotheuppergearofthepump.Whenthepumpisfirs
7、tstarted,rotationofgearsforcesairoutthecasingandintothedischargepipe.Thisremovalofairfromthepumpcasingproducesapartialvacuumonthesuctionsideofthepumpinlet.Herethefluidistrappedbetweentheteethoftheupperandlowergearsandthepumpcasing.Continuedrotationofthegearsforcest
8、hefluidoutofpumpdischarge.Pressureriseinaspur-gearpumpisproducedbythesqueezingactiononthefluidasitisexpelledfrombetweenthemeshinggearteethandcasi