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页数:5页
时间:2020-03-01
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1、Unit7FlowControlsThefunctionofaflowcontrolistocontrolthevolumeoffluidthatpassesacertainpointinthecircuit.Aflowcontrolisactuallyavalve.Aflowcontrolmightbecomparedtotheheatregisterinahome.Ifitisopenedonlyasmall"mount,onlyasmallquantityofhotaircancomeout;but
2、ifitisopenedwidely,thehotairrushesout.Theregistercanberegulatedfromcompletelyclosedtofullyopeninsmallsteps.Aflowcontrolisusedtocontrolthepistonspeedofpowercylinders,thespeedatwhichthespoolofapilotvalveshifts,thetimingcycleonatimingvalve,andthespeedatwhich
3、theshaftofafluidmotorrevolves.Aflowcontrolisasimpledevice,butitplaysaveryimportantroleinafluidpowercircuit・Sincebothairandhydraulicflowcontrolsarestudiedinthischapter,thetypesofflowcontrolvalvesthatareusedinindustryshouldbestudiedalso.Althoughmanypneumati
4、cflowcontrolsaredesignedforairpressuresupto150psi,theyarealsousedforlow-pressureoilserviceupto500psi;itisrecommendedthatpneumaticflowcontrolsbeusedforpneumaticserviceandthathydraulicflowcontrolsbeusedforpneumaticserviceandthathydraulicflowcontrolsbeusedfo
5、rpneumaticserviceandthathydraulicflowcontrolsbeusedforhydraulicservice.TYPESOFFLOWCONTROLSFlowcontrolscanbedividedintothreetypes:1.Metering-intype(Fig.l).2.Metering-outtype(Fig.2,Fig.3,andFig.4).3.Metering-in-both-directionstype(Fig.5).4.^Bleed-off'type(F
6、ig.l).Fig.1.Metering-intypeofvalve.Inthemetering-intypeofflowcontrol,thefluidismeteredonitswayintothedevicethatitisgongtocontrol(seeFig.l).Themetering-outtypeofflowcontrolmetersthefluidasitleavesthedevicethatitisgoingtocontrol(seeFig.2).Thisisoftencallede
7、xhaustmetering.Themetering-in-both-directionstypeofflowcontrolmetersthefluidinbothdirections(seeFig.5).Mostofthemeter-intypesofflowcontrolvalvesareusedforhydraulicservice,andmanyofthemeter-outtypeofflowcontrolvalvesareusedforpneumaticservice・Manyofthistyp
8、earealsousedforhydraulicservice•Themeter-in-both-directionstypeofflowcontrolvalvesisnotusedtoagreatextentinindustrialfluidpowersystems.'Bleed-ofiTtypesofbleedoffapredeterminedamountofoil,whichisunderpressure・Flowcon
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