优先流量阀

HIGHWAYHydraulicsAnyonewhohasattemptedalongjourneyinacarwillnoticethattheflowoftrafficaffectshowquicklyandsafelyyouarriveatyourdestination.Therearevariouswaysthathighwayagenciesseektocontrolthesetwoelements.Speedcamerasslowdriversdowntoenhancesafety,variablespeedlimitskeepthetrafficflowataconstantanddiversionslimittheweightoftrafficonanyroad.Someofthesemeasuresaremoreeffectivethanothers.Itwouldbegreatifwecouldaccuratelypredictthetimeittakestogetfrom‘A’to‘B’.Unfortunatelyduetorestrictionsandaccidentsourjourneysbecomemoredifficultandlessefficient.Thankfullywedonothavetodealwiththerandomvariablescausedbyhumanfrailtieswhenutilisinghydraulicswithinamachineprovidedthedesignerusesthebestavailableflowcontrolvalveswithinhissystem.Inhydraulicsitisimportanttocontroltheflowofoiltoaugmentthesafetyandefficiencyofamachine.Theresultswillvarydependingontheaccuracyandrepeatabilityofthevalvesused.Itisimportanttounderstandthefunctionandoperationofthedifferenttypesofflowregulatorbeforeapplyingthem;fromthesimpleneedlevalvetotheproportionalpressurecompensatedprioritydevice.Eachtypehasitsplaceandthereareapplicationsthatwarrantthedifferingcomplexity.WeunderstandthatflowtakesplacefromhighpressuretolowpressureandtheamountofflowisdictatedbytheFigure1.RestrictivetypeflowregulatorINLETPORTREGULATEDPORTNeedleValve-setsflowrate,createscontrollingpressuredropCompensatorSpoolSleeveRadialMeteringHolesBalanceofpressuresateachendofthespoolcontrolsitsposition-maintainingaconstantflowthroughthemeteringholes.Figure2.By-passtypeflowregulatorINLETPORTREGULATEDPORTBY-PASSPORTFigure3.PrioritytypeflowregulatorINLETPORTREGULATEDPORTBY-PASSPORTRadialMeteringHolesBy-PassRadialMeteringHolesRegulatedwarrantaugmentpressuredifference.Byintroducingrestrictionsintothelinewecancontroltheflowprovidedtheexcessflowisgivenameansofescape.Withaneedlevalvetheflowwillnotbecontrolleduntiltheinletpressurereachesapointatwhichanupstreamreliefvalveopensorapumpcompensatoroperatestoreducetheinletflowandmaintainabalance.Theflowacrossaneedlevalvedependsonthepressuredifferenceacrossitsochangesinoutletpressurewillhaveanimpactonthecontrolledflow.Toovercomethisproblemcompensatorsofvariousguisesareintroducedintothesystem.Therearethreemaintypes;Restrictivestyle,By-passstyleandPrioritystyle.Therestrictivestyleflowcontrolconsistsofaneedlevalveandcompensatorelement.Thecompensatorcanbesituatedaftertheneedlevalve(Seefigures1&4).Fluidpressureatthehigh-pressuresideorinlettotheneedlevalveissensedononeendofthecompensatingspoolandpressureatthelowerpressuresideoroutletissensedbytheotherendofthesamespool.Thisspoolisusuallyoffsettotheopenpositionbyaspring.Theflowthroughthevalveisdeterminedbythepositionoftheneedleasthecompensatorwillalwaysensurethatpressuredropacrosstheneedleisconstant,usually7bar.Openingtheneedlewillpermittheflowtoriseuntilthepressuredropexceedsthesettingofthecompensatorcausingittoshiftclosingaringofholesinitssleeveandthuslimitingtheflow.Astheflowthroughthevalvewillbelowerthantheflowbeingdeliveredbythepumptheinletpressurewillrisetoapointwhereanupstreamreliefwillopenfeedingexcessflowtotankorapumpcompensatorbacksoffreducingtheinletflowtothatrequiredtosatisfytheflowsettingoftheflowregulator.Theby-passstyleofflowcontrol(Figure2&5.)againconsistsofaneedlevalveandcompensatorelementbuthasathirdporttoallowtheexcessflowtopasstotankatworkingpressureasopposedtomaximumreliefvalvesettinginthecaseoftherestrictivestyle.Thecompensatorspoolisbiasedclosedbyaspring,inletpressureactstoopenthespoolagainsttheactionofthespringandpressuredownstreamoftheneedlevalveactstoclosethespoolinthedirectionofthespring.Flowthroughthecompensatorspoolgoestotank.Asthepressuredropincreasesacrosstheneedlevalvethepressuredifferenceissensedacrossthecompensatorspooluntilitmovestoopentheinlettothetankport.Increaseinoutletpressurewilltendtoreducetheflowacrosstheneedlevalvebuttheco-respondingchangeinpressuredropwillcausethecompensatortorestrictthelinebetweentheinletandthetankline.Inthiswaythespoolwillmeterthebypassflowtomaintainaconstantcontrolledflowthatrelatestotheforceexertedbythespringandtheorificesizecreatedbytheneedlevalve.Withthistypeofflowregulatoritisimportantthatthetanklinepressureiskepttoaminimumasthismayincreasetheflowthroughtheregulatedlineabovethatrequired.Theprioritystyleflowcontrol(Figure3&5.)issimilartothebypassstyleexceptthatitallowstheexcessoiltobeusedforotherfunctionseveniftheworkingpressureforthisfunctionishigherthanthecontrolledflowpressure.TheflowfromthepumpenterstheinletportandpassesacrossFigure5.Prioritytypecartridgeflowregulatoralsousedforby-passoperation.INLETPORTREGULATEDPORTNeedleValve-setsflowrate,createscontrollingpressuredropCompensatorSpoolSleeveRadialMeteringHolesBy-PassBalanceofpressuresateachendofthespoolcontrolsitsposition-maintainingaconstantflowthroughthemeteringholes.BY-PASSPORTRadialMeteringHolesRegulatedFigure4.RestrictivetypecartridgeflowregulatorINLETPORTREGULATEDPORTNeedleValve-setsflowrate,createscontrollingpressuredropCompensatorSpoolSleeveBalanceofpressuresateachendofthespoolcont