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1、10HydraulicmachineryandpumpHydraulicmachineryaremachinesandtoolswhichusefluidpowertodowork.Heavyequipmentisacommonexample.Inthistypeofmachine,high-pressureliquid-calledhydraulicfluid-istransmittedthroughoutthemachinetovarioushydraulicmotorsandhydrauliccylinders.Thefluidiscontro
2、lleddirectlyorautomaticallybycontrolvalvesanddistributedthroughhosesandtubes.Thepopularityofhydraulicmachineryisduetotheverylargeamountofpowerthatcanbetransferredthroughsmalltubesandflexiblehoses,andthehighpowerdensityandwidearrayofactuatorsthatcanmakeuseofthispower.Hydraulicma
3、chineryisoperatedbytheuseofhydraulics,wherealiquidisthepoweringmedium.Pneumatics,ontheotherside,isbasedontheuseofagasasthemediumforpowertransmission,generationandcontrol.HydrauliccircuitsForthehydraulicfluidtodowork,itmustflowtotheactuatorandormotors,thenreturntoareservoir.Thef
4、luidisthenfilteredandre-pumped.Thepathtakenbyhydraulicfluidiscalledahydrauliccircuitofwhichthereareseveraltypes.Opencentercircuitsusepumpswhichsupplya1010continuousflow.Theflowisreturnedtotankthroughthecontrolvalve'sopencenter;thatis,whenthecontrolvalveiscentered,itprovidesanop
5、enreturnpathtotankandthefluidisnotpumpedtoahighpressure.Otherwise,ifthecontrolvalveisactuateditroutesfluidtoandfromanactuatorandtank.Thefluid'spressurewillrisetomeetanyresistance,sincethepumphasaconstantoutput.Ifthepressurerisestoohigh,fluidreturnstotankthroughapressurereliefva
6、lve.Hydraulicpumpssupplyfluidtothecomponentsinthesystem.Pressureinthesystemdevelopsinreactiontotheload.Hence,apumpratedfor5,000psiiscapableofmaintainingflowagainstaloadof5,000psi.Pumpshaveapowerdensityabouttentimesgreaterthananelectricmotor(byvolume).Theyarepoweredbyanelectricm
7、otororanengine,connectedthroughgears,belts,oraflexibleelastomericcouplingtoreducevibration.Commontypesofhydraulicpumpstohydraulicmachineryapplicationsare;Gearpump:cheap,durable,simple.Lessefficient,becausetheyareconstantdisplacement,andmainlysuitableforpressuresbelow20MPa(3000p
8、si).Vanepump:cheapandsimple,reliable(especiallying-rot
