Chapter5HydraulicControlValves

5.1Introduction

5.2DirectionalControlValves

5.3PressureOperatedValves

5.4FlowControlValves

5.5ManifoldValvesandCartridgeValves

5.6Electro-HydraulicServoValves

5.7Electro-HydraulicProportionalValves

5.8Electro-HydraulicDigitalValves

Chapterlist5.1Introduction

5.1.1Basiccharacteristics

5.1.2Classification5.1.3Basicrequirementsforhydraulicvalves5.1.1Basiccharacteristics

Thetypesofcontrolvalvesusedtodayaretoonumeroustobementioned.Mostvalves,however,performthreeprimaryfunctionsinthehydraulicsystem:tocontroltheoilpressure(pressurecontrolvalves),theflowrate(flowcontrolvalves)andthedirectionofoilflow(directionalcontrolvalves)inthesystemtoensuretheactuatorsinproperworkingonordertheloadrequested.Althoughtherearemanytypesofhydrauliccontrolvalvesandtheymightbequitedifferentfromeachotherineitherthefunctionsorconfigurations,thereexistbasiccharacteristics.

1.Instructure,allhydrauliccontrolvalvesconsistofthevalvebody,thevalvecore(spool,coneorball)andtheoperatingelementsusedtocontrolthevalvecore.ThethreebasictypesofcoresareshowninFig.5-1.2.Inoperatingprinciple,theorificeflowformula

shouldbekepttruefortheorificesize,thepressuredifferencesbetweentheinletandoutletandtheflowrateofthroughthevalves.Fig.5-1Configurationtypesa)Spoolvalveb)Conevalvec)Ballvalve

5.1.2Classification

Thehydrauliccontrolvalvescanbecategorizedaccordingtodifferentclassificationattributes,seeTab.5-1.Tab.5-1ClassificationofhydrauliccontrolvalvesClassificationattributesTypesContentsThefunctionsThepressurecontrol

Relief,pressurereducing,sequence,proportionalpressurecontrol,pressureswitch,etcTheflowcontrol

Throttle,speedcontrol,overflowthrottle,dividing,combining,proportionalflowcontrol,etcThedirectionalcontrol

Check,pilot-operatedcheck,

directional,proportionaldirectionchange,etcThemanipulationManually

Handleorhandwheel,pedal,leverMechanically

Skid,spring,hydraulic,pneumaticElectrically

Thesolenoid-operated,electro-hydrauliccontrolTab.5-1ClassificationofhydrauliccontrolvalvesConnectionThetubingThetubingandtheflangedSub-platemountingormodular

Single/double-platemounting,integrationandsandwichvalvesThecartridgeThescrew,andtheflangedControlTheconstantcontrolvalvesorswitchesThepressurecontrol,theflowcontrol,thedirectionalcontrolTheelectro-hydraulicproportionalcontrolTheelectro-hydraulicpressure/flow/directional/combinedvalvesTheservo-controlTheelectro-hydraulic,air-hydraulic,mechanical-hydraulicThedigitalcontrol

Thedigitalcontrolpressure/flow/directionalcontrolvalves5.1.3Basicrequirementsforhydraulicvalves1.Sensitive,credible,andlowimpactandvibration;2.Lowresistancewhentheorificeisopenedcompletely,andhasgoodsealingabilitywhentheorificeisclosed;3.Controllableparameters(suchasthepressureandtheflowrate)shouldbestableandinsensitiveunderdisturbance;4.Compactinstructureandgoodininstallation,

adjustmentandapplications.5.2

DirectionalControlValves5.2.1In-lineCheck

5.2.2DirectionalcontrolvalvesTherearetwotypesofgeneraldirectionalcontrolvalves:in-linecheckanddirectionchanging.5.2.1In-lineCheck

Thein-linecheckvalvesinclude:thegeneraltypechecksandhydraulicoperatedcheckvalves.1.Thein-linecheckvalvesofgeneraltypeFunctions:Thisvalveallowsfreeflowinonedirectionandpreventsflowinthereversedirection.Fig.5-2showsageneraltypecheckvalveinathreadedpipeconnection.

Fig.5-2CheckvalveConfiguration

b)Symbol1-Valvebody2-Valvecore3-Spring

2.HydraulicoperatedcheckvalvesBesidesinletandoutletportthereisapilot(remote)port(suchasFig.5-3)、Fig.5-3Hydraulic-operatedGeneraltypecheckvalveb)Hydraulicoperatedcheckvalve1,6-Spring2,8-Valvecore3,9-Handspike4,10-Controlpiston5－Smalldischargedcore7－Springseat

Notethat

theportshouldbeconnectedtothereservoirwhenitisnotworking,otherwiseitcannotbereturned.5.2.2Directionalcontrolvalves

Functions:

Accordingtothecoremotionsrelative

body,adirectionalcontrolvalveinahydraulicsystemisusuallyusedtocontroltheoilpathsthatcanbeconnected,ortheoilflowdirectionthatcanbechanged,whichallowstheactuatortobestarted,stoppedortheoilflowdirectiontobeshifted.2.Classification

Byconfiguration:rotary,slidingorball;(2)Byports:twoports,threeports,fourportsandsoon;(3)Byrelativeoperatingposition

ofspoolinthevalvebody.Therearetwo,three,andfourpositions;3.Theconstructionofspoolordirectionalcontrolvalve

ThecommonconfigurationsofspoolordirectionvalvesareshowninTab.5-2.Theirdifferenceslieinthewaysandpositionstheypossess.Twoorthree-positionvalvesmeanthattheirvalvecoreshavetwoorthreedifferentworkingpositions;similarly,two,threeorfourwayvalvesindicatethattherearetwo,three,orfouroilpathsonthevalvebodywhichareseparatedfromeachotherandconnectedwiththeirindependentoillines.Thefunctionofthedirectionvalvesdependupontheirwaysandworkingpositions.(4)Bytheoperatingmeans:Thesevalvecoresmaybeoperatedbyadifferenceofoilpressureonthespool,ormanually,mechanically,electrically,orbyacombinationofthesemeans.Tab.5-2Configurationsofspooltypedirectionalcontrolvalves

4.Theoperatingmannersforspooltypedirectionalcontrolvalves

Theoperatingmannersforspooltypedirectionalcontrolvalvesinclude:manual-operated(ormechanical-operated),solenoid-operated,pilot-operated,electrohydraulic-operated,etc.SeeFig.5-4,Fig.5-5,Fig.5-6.Fig.5-4Three-position,four-waymanualdirectionalcontrolvalvea)Spring-centedspoolb)Steelball-centedspoolc)GraphicssymbolforSpring-centedspoold)GraphicssymbolforSteelball-centedspool

Fig.5-5Two-position,two-way

Solenoid-operateddirectionalcontrolvalvea)Configuration

b)Graphicssymbol

1-Solenoid2-Handspike3-Valvecore4-SpringwhenthesolenoidisnotenergizedwhenthesolenoidisenergizedFig.5-6Electric-hydraulicoperateddirectionalcontrolvalve

1-Valvecoreoperatedbyhydraulicpressurized2，8-Checkvalve

3，7-Throttlevalve

4，6-Solenoid5-ValvecoreoperatedbySolenoid

5.Functionsofneutralposition

Three-positionvalveconsistsoftwoextremepositionsandacenterposition.Thetwoextremepositionsaredirectlyrelatedtotheactuator'smotion.Thecenterpositionofthedirectionalcontrolvalveisdesignedtosatisfyaneedofthesystem.Forthisreason,adirectionalcontrolvalve'scenterpositioniscommonlyreferredtoasaneutralconditionasshowninTab.5-3.

Tab.5-3NeutralconditionsofdirectionalcontrolvalvesTypeNeutralconditionSymbolFeaturesandapplicationFour-wayFive-wayOAllportsareblockedandthetwoendsofthecylinderaresealed.Pumpflowisn’treturnedtothereservoir.CanbemountedinparalleltoperformcomplexoperationHAllportsareconnectedtoeachother.Allowsfreemovementofanactuatorwhilepumpflowisreturnedtothereservoir.YAfloat-centerspool.PortPisblockedandportsA,B,andTareconnected.Allowsfreemovementofeachactuator.Pumpflowisn’treturnedtothereservoirJOneendofthecylinderissealed;theotherisconnectedtothereturnedoil.Thesystemisn’tunloadedCPortsPandportAareconnected,whileBandTareblocked.Oneendofthecylinderissealed.Pumpflowisn’treturnedtothereservoir.PPortTisblockedandportsA,B,andPareconnected.Canbeusedasanelementofdifferentialcircuitforhydrauliccylinder.KPortsP,A,Tareconnected,whileportBisblocked.Oneendofthecylinderissealed.Pumpflowisreturnedtothereservoir.XAllportsareconnectedtoeachotherwithahalfopenthrottleorifice.Allowsfreemovementofanactuatorwhilepumpflowisreturnedtothereservoirunderagivenpressuredrop.

Tab.5-3NeutralconditionsofdirectionalcontrolvalvesMPortsPandTareconnectedandAandBareblocked.Atandem-centerconditionstopsthemotionofanactuator,butallowspumpflowtoreturntoreservior.UThetwoendsofthecylinderareconnectedtoeachother.Thesystemisn’tunloaded.Returnedoilportissealed.NOneendofthecylinderisconnectedtothereturnedoil,theotherissealed.Thesystemisn’tunloaded.

Notes:Intheanalysisandselectionoftheneutralconditions,thefollowingfactorsaremainlyconsidered:(1)Pressure-holding.(2)Unloadingcondition.WhenportsPandTareconnected,thesystemisunloading.(3)Thestabilityandprecisionduringthedirectionalshift.(4)Startupstability.(5)Thecylinderneedsata‘float’conditionorcanstopatanyposition.5.3PressureOperatedValves5.3.1

Reliefvalves5.3.2

Pressure-reducingvalve5.3.3Sequencevalves

5.3.4Pressurerelay

5.3.1

ReliefvalvesPressureoperatedvalves,actuatedbyforcesinducedbythepressureoffluidandcontrolsign,areusedtoperformaparticularfunctionorcontroloilpressureinahydraulicsystem.Thecommonpressureoperatedvalvesinclude

reliefvalves,pressure-reducingvalves,sequencevalvesandpressureswitches.

Reliefvalvesaredevicesinstalledinacircuittomakeitcertainthatthesystempressuredoesnotexceedsafetylimits.Forsafety,thereliefvalveisusuallyinstalledascloseaspossibletothepump,withnoothervalvesbetweenthereliefvalveandpump.Reliefvalvescanbedividedintwocategories:direct-actingandpilot-operated.

1.Configurationandoperation（1）Direct-actingtype

Fig.5-7Direct-actingreliefvalvea)Configurationb)Graphicsymbol1-Reguatingscrew2-Spring3-Uppercover4-Valvecore5-Valvebody

-theorificeisdenoted;q-theflux;

p-inletpressure,-therigidityofspring;-pre-compression;

D-thediameterofcore.

-crackingpressure.Inletpressureisdenotedbyatthefull-flowandthestablehydraulicdynamicforceby,thentheforcebalanceequationscanbeobtainedbelow:(a)Theforcebalanceequationtobeginopening

（5-1）(b)

Thereliefforcebalanceequation

（5-2）(c)Thepressure-flowrateequation（5-3）Bycombiningequations(5-7)and(5-8),inletpressurepcanbecalculatedunderdifferentflowrates.Noteheretwopoints:

(a)theopeningpressurepkisadjustablebyspringpre-compressionx0andbycontrollingtheinletpressurep,whichiscalledadjustmentspring;(b)thedirect-actingvalveisdesignedbyacore(poppetorballheld)exposedtothesystemfluid

pressureononesideandopposedbyaspringofpresetforceontheother.Soitneedsabiggerspringforceforahigherpressureorflowratesystem.Ifsotheabilityofspringwillbelowerandconfigurationisdifficult.Inpractice,therearefewdirection-actingvalves.(2)Pilot-operatedtype

Fig.5-8Pilot-operatedrelief

Configurationb)Graphicsymbol1-Damporifice2-Valvecoreofpilot3-Springofpilot4-Springofmainvalve5-Mainvalvecore

Pilot-operatedreliefvalvesareusedforthesystemswhichrequirehighpressureandlargeflowrate.TheircommonconstructionsareshowninFig5-8.Apilot-operatedreliefvalveoperatesintwostages：apilotstageandamainstage.Themainvalvedisplacementdependsupontheoilpressuredifferentialonthetwosidesofthemainvalve.Thestaticcharacteristicsofapilot-operatedvalvecanbedescribedbytheflowingfiveequations.（5-4）（5-5）（5-6）（a）Mainvalveforcebalanceequation

（b）Pressure-flowrateequationforthemainvalveorifice（c）Forcebalanceequationforthepilotvalvecore

（d）Pressure-flowrateequationonpilotvalve

（5-7）（e）Pressure-flowrateequationforthedampingorifice

（5-8）2.Basiccharacteristicsofreliefvalves

(1)RangeofpressureregulationPressureadjustedisstableandchangescontinuouslyupanddown.Thereisnojumporsluggish.

(2)Pressure-flowratecharacteristics

Thecharacterofinletpressureofreliefvalvevaryingwiththeflowrateisknownasthepressure-flowratecharacteroropened-closedcharacterasshowninFig.5-9.

(3)ExcessivepressureflowrateadjustmentFig.5-10showsthedynamiccharacteristiccurveswhentheworkingconditionschangefromthezeropressureandthezeroflowrateconditiontotheratedpressureandtheratedflowrate.Fig.5-9Pressure-flowratecharacteristicscurvesFig.5-10Dynamiccharacteristicscurve

5.3.2

Pressure-reducingvalve

Pressure-reducingvalvesareusedtodropthenormaloperatingpressureofamaincircuit

Therearethreekindsofpressure-reducingvalvesonrequest:

(1)tomaintainoutletpressureinvariableness,calledfixedvaluepressure-reducingvalves;(2)tomaintainaconstantpressuredifferentialbetweeninletandoutletports,calledfixedpressuredifferentialpressure-reducingvalves;(3)toproportionpressure-reducingvalveemployedtoensurethattheoutletpressureisproportionaltothatoftheinlet.Thefixedvaluesareappliedwidely.Theyareintroducedhere.1.ConfigurationandoperatingprincipleFig.5-11Pilot-operatedpressure-reducingvalveConfigurationb)Graphicsymbol1-Valvecoreofpilot2-Valvecoreofmainvalve3-Dampingorifice

2.FunctionsandfeaturesComparewithreliefvalves,theirdifferencesliein:

(1)Thepressure-reducingvalvesholdstheoutletpressureconstant,whereasthereliefvalveholdsthedesiredreducedpressureattheinlet;(2)Thepressure-reducingvalveisannormallyopenvalve,whilereliefvalvenormallya

closevalve;(3)Thepressureexistsinboththeinletandoutletportsofpressure-reducingvalves,sotheleakingoilfromthespringportofthepilotvalvemustbeinducedseparatelytothereservoir.

5.3.3Sequencevalves

1.Functions

Asequencevalveisusedtodirecttheflowoffluidtomorethanonepartofacircuitinsequence.

2.Operatingprinciple

AsshowninFig.5-12.Fig.5-12Sequencevalveoperateddirectly

3.Controlmanners:

Accordingtodifferentarrangementsoftheuppercoverorthebottomcover,fourcontrolmannerscanbeobtained:internalcontrolandexternaldischarged,internalcontrolandinternaldischarged,externalcontrolandexternaldischarged,andexternalcontrolandinternaldischarged,pleaseseeFig.5-14.Fig.5-14Fourcontroltypesofgraphicssymbolsa)Internalcontrolexternaldischargedb)Internalcontrolinternaldischargedc)Externalcontrolexternaldischargedd)Externalcontrolinternaldischarged4.Features:

Sequencevalvewithaninternalcontrolandinternaldischargedtypecanbeusedasacounter-balancevalveorabackpressurevalve;sequencevalvewithexternalcontrolandinternaldischargedtypeasanunloadingvalve;sequencevalvewithexternalcontrolandexternaldischargedtypeissimilartoapilot-operatedtwo-way,two-positionvalve.

Forasequencevalvewithinternalcontrolandexternaldischargedtypeorasametypeofreliefvalve,thecommonpointisthattheyarenormallycloseandthecoreopenactiondependsmainlyupontheinletpressure.Let’scomparethesequencevalve

withinternalcontrolandexternaldischargedtypewiththereliefvalve,theircommonsanddifferencescanbeconcludedasfollows:Thecommonpoints:

Asequencevalveofthesamecontroltypeisnormallyclose.Whetherthecoreinthevalvewillbeopendependsontheinletpressure.

Thedifference:Theoutletpressureoilforsequencevalveisusedtosupplypressureforsomeotherpartofahydraulicsecondarycircuit.

5.3.4Pressurerelay

1.Functions:

Itisanelementthatswitchesthepressureinthehydraulicsystemtoanelectricsignandallowsactuatorstoperformpredeterminedsequenceactionorsecurity.

Thisisaccomplishedbyitsjiggleswitchwhichwilloperatetoconnectorshutoffelectricalpathswhenthehydraulicpressurereachesthesettingofswitch.2.Configuration:Therearepistontype,spring-tubetypeanddiaphragmtype,etc.Fig.5-15isapressurerelaywithasingletouchpointpiston.

Fig.5-15Pressurerelaywithsingletouchpointpistona)Configuration

b)Graphicssymbol

1-Piston2-Mandril3-Regulatingscrew4-Microelectricalswitch

5.4

FlowControlValves5.4.1Operation5.4.2

Throttlevalves5.4.3Speed-regulatingvalvesandrelief-throttlevalves5.4.1Operation(5-9)

Thepressure-flowrateequationdiscussedinChapter2canberewrittenasfollows:ThecommonconfigurationsofthrottlingelementsareshowninFig.5-16.

Fig.5-16Orificestypesusedinthrottlevalvesa)Poppet(core)-shapedb)Triangle-notchc)Rectangled)Trianglecone-shaped5.4.2

Throttlevalves

ConfigurationandoperatingprincipleFig.5-17Throttlingvalve1-Valvecore2-Handspike3-Handle4-Spring

Athrottlevalvesisasimpleflowcontrolvalves.Athrottlevalveisvirtuallyequaltoavariableorifice.

2.Flowcharacteristicsandrigidity

(5-10)ThelargertheTvalueis,thebetterabilityofthevalveis.

UnderagivenflowareaA,pressuredifferenceisstillsensitivetotheoutsideload.Inahydraulicsystem,thepressuredropvarieswiththeloadfluctuation.Ifonesetstheratiototheflowrateincrementqastherigidityofthrottlingvalve,andnoteasT,thentheTcanbeobtainedby,pDpDpD

3.Application

Throttlevalvesareusuallycombinedwithfixeddeliverypumps,reliefvalvestoconstituteathrottlespeed-regulatingsystem.Thespeedcanbeadjustedbychangingthethrottleorificesize.5.4.3Speed-regulatingvalvesandrelief-throttlevalvesAsdescribedabove,theflowratethroughtheorificeissensitivetothepressuredropofthevalve,sopoorrigiditymayoccurtothrottlevalves.Forthisreason,thethrottlevalvesareonlyapplicableforthesmallloadchangeoccasionswhichrequirelessforspeed-stability.

1.Speed-regulatingvalvesFig.5-18showsaspeed-regulatingvalveoperationprinciple.Fig.5-18Operatingprincipleofregulatingspeedvalve

Staticequationsofaspeed-regulatingvalveinoperation,

（5-11）（5-12）（5-13）（5-14）Fig.5-19Bypassspeed-regulatingvalveoperationa)Configurationb)Graphicssymbolc)simplifiedgraphics2.Relief-throttlevalves(Bypassspeed-regulatingvalves)Fig.5-19indicatesarelief-throttlevalveoperationanditsgraphicsymbol.

1-Actuator2-Sefetyvalve3-Reliefvalve4-Throttlevalve5.5

ManifoldValvesandCartridgeValves5.5.1Manifoldvalves5.5.2Cartridgevalves5.5.1Manifoldvalves

Themanifoldvalvesaredesignedonthebasisofplatevalves.TheupperanddownsurfacesofeachhydraulicvalvearemadethesameastheundersideofaplatevalveasshowninFig.5-20a.

Asinglemanifoldvalveoperatesthesameasthecommonvalveinoperation.ButthedifferenceisthateachmanifoldhasfourportsP,A,BandT.Forasysteminstallation,variousmanifoldvalveswiththesamespecificationbutdifferentfunctionsaresplicedtogetheronarequestedsequenceonthehydraulicsystemchart,seeFig5-20b.

Fig.5-20Manifoldvalve

a)Configurationb)Graphicssymbol1-Thesolenoidoperatedvalvewiththree-positionandfour-way2-Bidirectionalhydrauliclock3-Twoinletportcheck-throttlevalve4-Pressure-reducingvalve5-Soleplate6－Hydraulicactuator5.5.2Cartridgevalves

Thecartridgevalvesarewildlyadoptedinthehydraulicsystemswithhighpressureandlargeflowrate.Severalcartridgevalvescanbeconnectedacompoundvalve.Comparedwiththecommonhydraulicvalves,thecartridgevalveshavethefollowingadvantages:1)Itprovidesalargeflowrate.Thelargestflowrateavailablehas10,000L/min,andthemaximumdiameterfortheflowareais200～250mm.Itisapplicableforlargeflowrateoccasionsrequired.2)Ithasacuteabilitytoresponseforthevalvecoremotionanhasagoodabilityforanti-blocking.3)Itperfectssealandhasasmallleakageandlowpressurelossviaorifices.1.OperatingprincipleandtheirbasicunitsBasicunits:avalvecore,abushing,aspring,theseals.

Threedifferentconfigurations:(1)directionalcontrolunits(Fig.5-21a),(2)pressurecontrolunits(Fig.5-21b),and(3)flowcontrolunits(Fig.5-21c)tomeetthedifferentcontrolneeds.

Allincludethreeports:twoaremainportsA,B,andthethirdiscontrolportX.

IfwenotethediameterofthevalvecoreasD,thediameterofthevalveseatholeasd,andtheactingareasofportsA,BandXas

AA

、AB、AXrespectively

：4)Itiscompactandsimpleinspaceandconfigurationandalsoeasytobestandardized.

Fig.5-21Basiccartridgeinsertsunits

1-Bushing2-Sealring3-Poppet(core)4-Spring5-Cover6-Resistancehole7-Poppet(core)regulatinga)Directionalcontrolvalveunitsb)Pressurevalveunitsc)FlowrateunitsThenon-dimensionalareas(arearatios):

,valveclosed，valveopened

Theworkingconditiononvalve:2.Pilotoperatedvalveandcoverboard

Thepilot-operatedvalveandthecoverboardarebothusedtocontroltheXporttorealizetheoilcircuitconnectionandvalvesopenedorclosedinacartridgeinsertunits.

(1)Forthedirectionalcontrolunits:thepilotoperatedcanbeasolenoidspool,orasolenoidballvalve.(2)Forpressurecontrolunits:thepilotoperatedcanbeapilot-operatedpressurevalve,asolenoid-operatedspoolvalve.(3)Forflowcontrolunits,solenoid-operatedvalvecanalsobeused,butshouldbeaddedwithastrokeregulatingrodonthecoverboardforthevalvecoretorestrictoradjusttheorificeandthustheorificeflowarea(Fig.5-21c).3.Applicationsofthecartridgeinsertvalve(1)Checkvalvesbycartridge

ConnectingdirectcontrolportXwithportAorportBcanbuildacheckvalveinadirectionalvalve.FortheconfigurationshowninFig.5-22b,whenfluidflowsfromAtoB,thevalveisclosed,butalsopermittingaleakagefrom

AtoBviatheannularclearancebetweenthetopofthevalvecoreandthebushinghole.ThesealingperformanceisnotsogoodasthatshowninFig.5-22a.Fig.5-22Cartridgeinsertcheckvalve

a)Positivedemonstrationb)ReversedemonstrationFig.5-23showsathree-way,two-positiondirectionalcontrolvalveunitsusedtocontroloildirection.Thepilotoperatedisasolenoidspoolvalve.AsisshowninFig.5-23a,whenthesolenoidisnotenergized,portXisconnectedtothereservoirviatheleftport(normalcondition)ofthetwo-way,two-positionvalve.

UnlikethedesignshowninFig.5-23a,whenthethree-way,two-positionvalveshowninFig.5-23bworksatitsrightposition,thepressureinportXisalwaysequaltothehigherpressureduetotheactionof‘shuttlevalve’.Inthiscase,whethertheoilpassesthroughportAorportB,thevalveisclosedandportsAandBareblocked.

(2)Two-way,two-positionvalvesbycartridgeFig.5-23Two-wayvalve

Fig.5-24Three-wayvalve

WhenelectromagnetYpowerlossWhentheelectromagnetYinthepower(3)Three-wayvalvesbycartridge(4)Four-wayvalvesbycartridgeFig.5-25Four-wayvalve

5.6Electro-hydraulicServoValves

AnElectro-hydraulicservovalvefunctionsasanelectro-hydraulictransferequipmentandalsoapoweramplifier,whichitisputintoalowerelectricalsignaltogetapowerfulhydraulicpressureenergyandrealizethepurposeofadisplacement,speed,accelerationandforcecontrolsforanactuators.Fig.5-26illustratesanozzleflapperelectro-hydraulicservovalve.（1）Theelectro-hydraulictransferequipment

Itcantransfertheinputelectricalsignalintoatorqueoutput(motor)orlineardisplacementoutput(hydrauliccylinder).

Fig.5-26Nozzleflapperelectro-hydraulicservovalve

1-Fixedthrottleorifice2-Feedbackpole3-Gagbit4-Magnetizer5-Springpipe6-Permanentmagnet7-Nozzles8-Baffle9-Mainvalve（2）Thehydraulicpoweramplifies(seeFig.5-27)

Fig.5-27Hydraulicamplifier

1-Baffle2-Nozzles（3）Afeedbackandbalancemechanism

Asdescribedabove,thespoolvalveisbalancedbytheelasticreactionforceofthefeedbackspringpiece(baffle),soitisaforcefeedbacktype.5.7Electro-hydraulicProportionalValves5.7.1Pressurecontrolelectro-hydraulicproportionalservovalve5.7.2Flowcontrolelectro-hydraulicproportionalvalves5.7.3Electro-hydraulicproportionaldirectionalcontrolvalves5.7.1Pressurecontrolelectro-hydraulicproportionalservovalve

TheproportionalpressurepilotvalveofFig.5-28canbeusedtoconnectwithacommonrelief,pressurereducingorasequencevalvepoppet(core)tobecomevirtuallyanypilotcontrolledpressuredevice.

Electro-hydraulicproportionalvalvesperformthefunctionsofremote,computercontrolsforhydraulicparameters(pressure,flowrateanddirection)

inproportiontoinputelectricsignal.

Theperformanceofthenewlydevelopedelectro-hydraulicproportionalvalvesisbetterthancommonhydrauliccontrolvalvesbutitisinferiortoelectro-hydraulicservovalves.Fig.5-28Electro-hydraulicproportionalpressurepilot

1-Valvepoppet(core)2-Loadedspring3-Handspike4-Proportionalvalvewithso