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Product:EXCAVATORModel:235BEXCAVATOR9PCConfiguration:235BEXCAVATOR9PC00001UP(MACHINE)POWEREDBY3306ENGINE

SystemsOperationSUPPLEMENTFOR235BEXCAVATORMediaNumberSENR327800 PublicationDate01/01/1986 DateUpdated11/10/2001

SystemsOperation

Introduction

Themajorchangewiththe235Bistheincreaseinnetenginehorsepowerfrom195to215hp.Mostofthehydraulicchangesarearesultoftheincreaseinhorsepower.

Thissupplementmanualcoversthenewcomponentsinthehydraulicsystemforthe235B,someofwhichcomewiththeadditionoftheincreasedliftsystemasnotedinthechartbelow.

Aspartoftheincreasedliftsystemonly,aselectorvalve(4)isusedtodirectandcontrolsignalpressureforincreasedlift,forspeedanddirection,andforthepumpservos.Aspartoftheincreasedliftsystemonly,stickcheckandventvalvesareprovided,alongwiththeboomcheckandventvalves,tomaintainexactcontrolbyreducingdrift.

Thesummingvalve(14)isalsonowadjustablesothatimplementpressuresurgescanbepreventedfromdisruptingmachineperformance.

IncreasedLift

RIGHTHANDCONSOLE1.Switch.

Theincreasedliftsystemincreasesimplementworkingpressureforincreasedliftwhilereducingpumpflowforoptimumcontrolofboomandstick.

Increasedliftisenergizedbymovingswitch(1)(locatedontherighthandconsole)totheONposition.Thisenergizesasolenoidinselectorvalve(4)whichallowsasignaltotheservocontrolvalveforpumps(13).Thisinturndestrokespumps(13).Atthesametime,valve(4)allowsasignaltothemainreliefvalve(12).Thisincreasesthemainreliefsettingfrom27600kPa(4000psi)to31000kPa(4500psi).

SELECTORVALVE(LocatedonLeftSideofHydraulicTank)4.Selectorvalve.5.Trackbrakevalve.12.Mainreliefvalve.

SelectorControlValve(OnlyWithIncreasedLift)Selectorcontrolvalve(4)isastandardcomponenton235BExcavatorswiththebackhoeattachment.Dependingonmachineoperationand/orimplementloads,valve(4)doesthefollowing:

1.Basedonapilotsignalfromcontrolvalve(2)forspeedanddirection,directssignalpressuretoincreasethesettingofthemainreliefvalve(12)from276001030kPa(4000150psi)to310001030kPa(4500150psi)forspeedanddirectioncontrol.Atthesametimeitdirectspilotoiltothetrackbrakevalve(5)toreleasethetrackbrakes.

2.Directssignalpressuretoincreasethesettingofthemainreliefvalve(asabove)whiledecreasingpumpflowduringincreasedlift.

3.Controlsthepressuresignalfromtheunderspeedvalve(7)andsummingvalve(14)totheservosofpumps(13).

SelectorControlValveForwardTravelSignal

SPEEDANDDIRECTIONCONTROLVALVE2.Controlvalve(speedanddirection).

SELECTORANDTRACKBRAKEVALVES4.Selectorvalve.5.Trackbrakevalve.15.Outletport(signaloiltomainreliefvalve).20.Outletport(pilotoiltosummingvalve).23.Inlet(pilotoil).26.Inlet(FORWARDtravelsignal).32.Inlet(REVERSEtravelsignal).33.Linetotrackbrake.34.Linefromport(19)tovalve(5).35.Pilotoiltopilotcontrolvalves.36.Oilreturntotank(frompilotvalves).

Signaloilfromspeedanddirectioncontrolvalve(2)entersvalve(4)atinlet(26)andshiftsspool(29)totheleft.Pilotoilentersvalve(4)atinlet(23).Withspool(29)positionedleft,pilotoilpressurethroughpassages(21)and(24)andchamber(27)isallowedinpassage(25)ofspool(29)andchamber(30)topassage(18)ofthevalve.Thisallowspressureoilthroughoutletport(19)andline(34)andontovalve(5)forthetrackbrake.Pilotoilexitsvalve(5)throughline(33)toreleasethetrackbrake.Atthesametimetheparkingbrakeisbeingreleased,pilotoilpressuremovesvalveball(16)toallowpilotoilatoutletport(15).Thisincreasesmainreliefvalve(12)settingfrom276001030kPa(4000150psi)to310001030kPa(4500150psi).

Pilotoilfromchamber(27)isalsoinpassage(31)andatlocation(28).[Passage(17)wouldappearinoppositeviewofsectionAA.]Pilotoilpressureinpassage(17)leavesoutletport(20)asasupplyofpilotoilforsummingvalve(14).

SelectorControlValveReverseTravelSignal(notshown)

Signaloilfromspeedanddirectioncontrolvalve(2)entersvalve(4)atinlet(32)andshiftsspool(29)totheright.Pilotoilpressurefromchamber(27)isthenallowedpastspool(29)intochamber(30)andpassage(18).Fromthispoint,pilotoilpressureworksthesameasfortheFORWARDtravelsignal.

SelectorControlValveIncreasedLiftSignal

RIGHTHANDCONSOLE1.Switch.

Inheavyliftapplicationswhereanincreaseinliftingforceisneeded,switch(1)ontherighthandconsoleismovedtotheONposition.Thisenergizessolenoidvalve(41)whichinturnallowssignaloilpressuretotheservosofpumps(13)andtomainreliefvalve(12).

SELECTORANDTRACKBRAKEVALVES4.Selectorvalve.5.Trackbrakevalve.12.Mainreliefvalve.15.Outletport(signaloiltomainreliefvalve).20.Outletport(pilotoiltosummingvalve).23.Inlet(pilotoil).38.Outletport(signaloiltoservosofpumps).41.Solenoidvalve.

Pilotoilentersvalve(4)atinlet(23)andflowsthroughpassages(21)and(24)tochamber(27).Fromchamber(27),pilotoilflowsthroughpassage(31)tolocation(28)[passage(17)wouldappearinoppositeviewofsectionAA].Pilotoilpressureinpassage(17)leavesoutletport(20)asasupplyofpilotoilforsummingvalve(14).

Whensolenoidvalve(41)isenergized,thevalvespoolretracts(movestotheright).Pilotoilfromchamber(27)andpassage(31)thenflowsthroughchamber(42)andpassage(39)tochamber(40)ofvalve(41).Pressureoilisallowedthroughchamber(40)topassage(44),whichmovesvalveball(43).Thisallowspressureoilatport(38)totheservosofpumps(13).Thisinturnreducespumpoutputflowformoreprecisecontroloftheimplements.Also,withsolenoidvalve(41)energized,pilotpressureisallowedfromchamber(40)throughapassageatlocation(37).(ThepassagewouldappearinanoppositeviewofsectionCC.)Pressureoilthenmovesvalveball(16)toallowpressureatport(15)tomainreliefvalve(12).Thereliefsettingisincreasedto31000kPa(4500psi)from27600kPa(4000psi).

Theendresultoftheaboveoperationisthatthestick,boomandbucketmovementwillbeslowerformorecontrol,buttherewillbeincreasedliftingforceavailable.

HYDRAULICPUMPS13.Frontandrearpumps.

SelectorControlValveSummingorUnderspeedSignal

Selectorcontrolvalve(4)receivesasignalfromsummingvalve(14)inthecaseofasuddenpressureincreaseorasignalfromunderspeedvalve(7)whentheenginespeedhasloweredtoapproximately1940rpm.Valve(4)directseitherofthesesignalstotheservosofpumps(13)forreducedpumpflow.

Valve(4)alsoservesthepurposeofdirectingpilotpressureoiltothesummingvalve(14)foruseasasignaloil.

Operation

SELECTORVALVE4.Selectorvalve.14.Summingvalve.20.Outletport(pilotoiltosummingvalve).23.Inlet(pilotoil).38.Outletport(signaloiltoservosofpumps).45.Pilotreliefvalve.46.Inletport(underspeedsignal).47.Inletport(summingsignal).48.Line(signal).49.Line(signal).

Pilotoilpressureenterspassage(21)throughinletport(23)oftheselectorvalve.Theoilpressureisinpassage(24),chamber(27)andpassage(31).Thepressureoilenterspassage(17)fromapassageatlocation(28)(wouldappearinoppositeviewofsectionAA).Pilotoilexitsport(20)toprovidepilotoiltosummingvalve(14).

Signaloilfromsummingvalve(14)throughline(48)entersatinlet(47)orunderspeedsignaloilthroughline(49)entersatinlet(46).Thesignaloilmovesvalveball(43)toblockpassage(44)andallowthepressuresignaloiltooutlet(38).Thisoilthenoperatesthepumpservostodestrokethefrontandrearpumps.

Orificecheckvalve(10)locatedbetweensummingsignalline(48)andselectorcontrolvalve(4)isusedtopreventtheunderspeedsignaloilfromenteringline(48)tothesummingvalve.

SUMMINGVALVE

14.Summingvalve.48.Line(signal).

UNDERSPEEDVALVE7.Underspeedvalve.49.Line(signal).

PilotReliefValve

Thepilotreliefvalve(45)ismountedonselectorcontrolvalve(4).Whenpilotoilpressurereaches2300kPa(335psi),pressureoilisventedthroughoutletpassage(22)totank.Exceptformountinglocation,thisvalvehasnotchangedfromearliermachines.Sincetheflowofoilinthepilotsystemissosmall,mostoftheoutputfromthepilotpumpgoesthroughvalve(45).

StickOperation(IncreasedLiftSystem)

STICKHYDRAULICSCHEMATIC

1.Stickcylinder.

2.Oillinefrommaincontrolvalve(7)(forstickIN)toheadendofstickcylinder(1).

3.Oillinetostickcheckandreliefvalve(4)fromrodendofstickcylinder(1).

4.Stickcheckandreliefvalve.

5.Oillinefromvalve(4)tomaincontrolvalve(7).

6.Oilventlinefromvalve(4)toventvalve(11).

7.Maincontrolvalve(stickcontrolvalvesection).

8.Pilotpressureoil(stickIN).

9.Spool.

10.Pilotpressureoil(stickOUT).

11.Ventvalve.

12.Pilotpressureoil.

Togivemoreexactcontrolduringliftingofheavyloads,thestickmustremaininastationaryposition[exceptwhenchangedbyactivationofstickcontrolvalve(7)].Thisisaccomplishedbytheuseofstickcheckvalve(4)andventvalve(11)installedinthelinetotherodendofstickcylinder(1).Checkvalve(4)willkeeptheINdriftofthestickassemblyasnearzeroaspossible.

STICKCONTROLLEVER

StickCheckandReliefValve

NOTE:Foroperationofboomcheckandreliefvalve,seeBOOMLOWERCONTROLinFormNumberSENR7901.

CHECKANDRELIEFVALVE(LeftSideofMachineinMainValveCompartment)4.Valve.

DuringstickOUT,pumpoilflowsthroughline(5)intopassage(16).Thisoilopenscheckvalve(18)andgoesoutpassage(13).Frompassage(13)pumpoilflowsthroughline(3)totherodendofstickcylinder(1).

Whenspool(9)incontrolvalve(7)ismovedtoNEUTRAL,valve(18)closes.Theweightoftheloadand/orstickassemblycausespressureinline(3),passage(13)andthechambeofspring(20).Oilpressure(duetotheload)andtheforceofspring(20)holdvalve(18)closed.Ifanexternalforceonthestickassemblycausesasuddenincreaseofpressure[approximately38000kPa(5500psi)],reliefvalve(15)opensandoilgoesoutpassage(14)throughareturnlinetothetank.ThelinereliefvalveforstickINisintheendofvalve(7).Valve(15)instickcheckandreliefvalve(4)isthelinereliefvalveforstickOUT.

DuringstickIN,oilflowofthemainsystemputspressureontheoilintheheadendofthestickcylinderthroughline(2).Returnoilfromtherodendofthestickcylindergoesthroughline(3)topassage(13).Whenspool(9)ismovedtothestickINposition,ventvalve(11)opensawayforreleaseofoilpressureinthechamberofspring(20).Oilpressureonshoulder(19)ofvalve(18)movesvalve(18)againsttheforceofspring(20).Theoilinpassage(13)goesoutpassage(16)tomaincontrolvalve(7)throughline(5).

CROSSSECTIONOFCHECKANDRELIEFVALVE

4.CheckandreliefvalveforstickIN.13.Oilpassage.14.Oilpassage.15.Reliefvalve.16.Oilpassage.17.Ventvalvesignalpassage.18.Checkvalve.19.Shoulder.20.Spring.

StickVentValve

CROSSSECTIONOFVENTVALVE11.Ventvalve.21.Spring.22.Plunger.23.Ball.24.Plug.25.Passage.26.Passage.27.Spool.28.Passage.

STICKVENTVALVE

4.Valve(stickcheckandrelief).11.Valve.29.Valve(boomvent).30.Valve(boomcheckandrelief).

WhenthepilotcontrolvalveisintheNEUTRALposition,thereisnooilpressureinpilotoillines(8)and(12).Spring(21)pushesspool(27)totheendofthevalvebore.Anyexternalforcethatpushesdownonthestickassemblyputspressureontheoilinline(3)fromtherodendofthestickcylinderandpassage(13).Checkvalve(18)isheldinplacebytheoilinthechamberofspring(20)andtheoilinline(6).Ball(23)andspool(27)inventvalve(11)preventsthisoilfromventing.WhenthepilotcontrolvalveleverispushedtowardstickINposition,thereisapressureincreaseinpilotoillines(8)and(12).Oilpressureinline(12)topassage(28)movesspool(27)againsttheforceofspring(21).Spoolmovementopensawayforoilflowfrompassage(25),throughthechamberforspring(21),throughpassage(26),toareturnlinetotank.Passage(25)alsocausesareleaseofoilpressureinthechamberforspring(20)incheckvalve(4).Checkvalve(18)opensforflowofreturnoilfromtherodendofcylinder(1)tovalve(7)andtoareturnlinetotank.

Inthestickcircuit,plunger(22)andball(23)havenouse(seeBOOMLOWERCONTROL,FormNo.SENR7735forapplication).Plug(24)isusedtosealofftheunusedpassage.

NOTE:Insituationswhereexcessdriftoccurs,makesureplunger(22)isinfarenoughtoseatball(23).

SummingValveThesummingvalveworkswiththeunderspeedvalvetocontrolpumpoutput.Theunderspeedvalvecontrolspumpoutputbasedonenginespeedonlywhilethesummingvalvecontrolspumpoutputbasedonlyonpumppressuresurges(suddenpressureincreases).

Inlets(7)and(10)areconnecteddirectlytothechambersinthecombinervalve.Inlet(7)isconnectedtothechamberfortherearpumpandinlet(10)isconnectedtothechamberforthefrontpump.Throughtheseconnections,anypressureincreaseinthechambersofthecombinervalveresultinapressureincreaseatinlets(7)and(10).Thepressuresarefeltbyloadpistons(5)and(14).Eachofthefourpistonsmovesindependently(separatelyfromeachother).

SUMMINGVALVE(RightSideofMachineNexttoHydraulicTankViewedfromBottomofMachine)

SUMMINGVALVE1.Outlettotank.2.Spring.3.Orifice(variable).4.Inletforpilotpressureoil.5.Loadpistons(twoforrearpump).6.Cap.7.Inletforcombinervalve.8.Slug.9.Adjustmentscrew.10.Inletfromcombinervalve.11.Spool.12.Outletforpumpsignalpressure.13.Passagetotank.14.Loadpistons(twoforfrontpump).

Thefourpistons(5)and(14)transmitpumppressuretospool(11).Inaddition,pilotpressurefrominlet(4)actsonthesurfaceareaofslug(8).Theseforcesarebalancedagainstthecombinedforceofsignalpressureoilfromoutlet(12)actingagainstthesurfaceareaofspool(11)andtheforceofspring(2)actingonspool(11).

Whenthecombinationofpressure(summing)[actingonpistons(5)andpistons(14)]gohighenoughtocausespool(11)tomove,variableorifice(3)openstoallowsignaloiltooutlet(12).

Outlet(12)isconnectedthroughalineandorificecheckvalvetotheunderspeedvalveandpumpservovalves.[Whenincreasedliftispartofthehydraulicsystem,outlet(12)isconnectedthroughalineandorificecheckvalvetotheselectorvalvealongwiththeunderspeedsignal.Dependingon

thelargerofthesignals,(summingorunderspeed),thatsignalgoestothepumpservos.]Whenthesummingpressurebecomeshigherthanthesignalpressurefromtheunderspeedvalve,thesignalfromthesummingvalvecausesthepumpstodecreasetheiroutput.Normallythesignalfromthesummingvalvetothepumpsisofshortdurationandhappensonlywhenthereisapressuresurge.

Tomakeachangeofthesummingsignalpressuretothepumps,useadjustmentscrew(9).SeeADJUSTINGOFSUMMINGVALVEintheTestingandAdjustingSection.

PilotControlValvesOilflowfromthepilotpump,atapressureof2300170kPa(33525psi),isusedtocontrolthemovementofthespoolsinthemaincontrolvalvesforboom,bucket,stickandswing.

Togivetheoperatortheabilitytocontrolthisflowandpressure,twopilotcontrolvalvesareinstalledinthepilotsystem.Oneofthesevalvesisintheleftarmrestandcontrolsthestickinandoutmovementandtherightorleftmovementoftheswingcircuit.Theotherpilotvalveisinstalledintherightarmrestandcontrolstheraiseandlowermovementoftheboomandtheopenandclosemovementofthebucket.

PILOTCONTROLVALVE1.Actuatorplate.2.Plungers(fourineachvalve).3.Retainer.4.Markusedfordisassemblyandassembly.

BOTTOMOFPILOTCONTROLVALVE5.OutletforboomRAISEorstickOUT.6.OutletforswingLEFTorbucketOPEN.7.OutletstickINorboomLOWER.8.Inletforpilotpressureandflow.9.Outletforreturnpilotpressureandflow.10.OutletforswingRIGHTorbucketCLOSE.

Thepilotvalvesaremanuallyoperatedandsendpilotoiltotheendofthespoolinthemaincontrolvalveselectedforoperation.

Therearefourpressurereducingtypevalveassembliesineachpilotvalve.Twovalveassembliesareneededtooperateeachofthefourimplements.

Whenacontrolleverismoved,aplungerispusheddowninthepilotvalve.Movementoftheplungercausesavalvestemtomovedownandopenapassageforpilotoiltogotooneendofamaincontrolvalvespool.Thepressureoilattheendofthemaincontrolvalvespoolmovesituntilapassageisopenedformainsupplyoiltotheimplement,cylinderormotor.

Thetwopilotvalvesarethesame.Threeofthefourvalveassembliesineachvalvearethesame.Thefourthvalve,whichisusedforstickINandboomLOWER,usesadifferentplunger.Identificationoftheportsisstampedonthebottomofthevalve.

BoomOperationHOLD

WhenthecontrolleversareinHOLDposition,alloftheplungersareinthesameposition.Pilotoilfromthepilotpumpgoesintothevalvethroughinlet(8)tochamber(25)andisstoppedbythepositionofstems(14)and(15).Passages(23)and(24)areopentotankthroughchamber(22)andoutlet(9).

Spring(20)pushesuponretainer(16)andplunger(2).Spring(18)holdsstem(14)downagainstretainer(16).Spring(19)pushesuponretainer(13)andplunger(12).Spring(21)holdsstem(15)downagainstretainer(17).Therearespacersbetweentheretainersandplungersthatareusedtochangetheforceofsprings(18)and(19).

PILOTCONTROLVALVE

1.Actuatorplate.2.Plungers(valve1,3&4).3.Retainer.5.Outlet.7.Outlet.11.Retainer.12.Plunger(valve2).13.Retainer.14.Stem.15.Stem.16.Retainer.17.Retainer.18.Spring(inner).19.Spring(inner).20.Spring(outer).21.Spring(outer).22.Chamber.23.Passage.24.Passage.25.Chamber.

BOTTOMOFPILOTCONTROLVALVE5.OutletforboomRAISEorstickOUT.6.OutletforswingLEFTorbucketOPEN(shovelDUMP).7.OutletforboomLOWERorstickIN.8.Inletforpilotpressureandflow.9.Outletforreturnpilotflow.10.OutletforswingRIGHTorbucketCLOSE.26.Passageforelectricalwires.

BoomRaise

WhenthecontrolleverismovedtotheboomRAISEposition,actuatorplate(1)tiltstotheright.Actuatorplate(1)pushesdownonplunger(2)

againsttheforceofspring(20).BoomRAISEstem(14)movesdownwithplunger(2).Theoilfrompumpinlet(8)nowcangothroughpassage(24)fromchamber(25)andoutpassage(5)totheraiseendofthemaincontrolvalveforboom.ThepressureofthisoilontheendoftheboomvalvespoolcausesittomoveintotheRAISEposition.

Theoilfromthechamberattheoppositeendofthemaincontrolvalvespoolforboomcomesbackthroughoutlet(7),throughpassage(23)instem(15)andthenintochamber(22)andbacktotank.

Oilpressureinoutlet(5)pushesupagainststem(14)andspring(18).Anyincreaseinpressureinoutlet(5)willpushharderagainststem(14)andspring(18).Asstem(14)movesup,passage(24)isclosedandtheflowofoilisstoppedtooutlet(5)[thepressureremainsinoutlet(5)].Atthispoint,stem(14)hasmovedoffretainer(16)andisbeingheldinapressuremodulatingposition.Thestemhasestablishedabalancebetweenthepressureinoutlet(5)andtheforceofspring(18).

Whenthecontrolleverhasmovedapproximately85%ofthedistanceforfullboomRAISE,plunger(2)makesdirectcontactwiththetopofstem(14).Whenthishappens,stem(14)ispusheddownuntilpassage(24)isagainopentopilotpressure.Fullpilotpressurenowgoestooutlet(5).

Whentheboomcontrolleverisreleased,spring(20)pushesuponplunger(2).Actuatorplate(1)returnsthelevertoHOLDposition.Stem(14)movesupbecauseretainer(16)hasmovedupwithplunger(2)andtheforceofspring(18)isless.Theoilinoutlet(5)canflowthroughpassage(24)andchamber(22)totank.

BoomLower

TheboomLOWERstem(15)operatesinasimilarmannertotheboomRAISEstem(14).Thedifferenceisinplunger(12)thatwillnevermakedirectcontactwithstem(15).Asaresult,fullpilotpressureof2300kPa(335psi)willneverbesuppliedtooutlet(7).

StickIn

Sincethepilotvalvesareidentical,theoperationofstem(15)willbethesameasboomLOWER.

StickOut,BucketOpenandCloseandSwingRightorLeftOperationofthepilotvalveforthesefunctionsisthesameasthatdescribedforboomRAISE.

PILOTCONTROLVALVE(StickandSwing)27.Pilotcontrolvalveforstickandswing.28.Outletlinetotank.29.PilotoillineforstickIN.30.PilotoillineforswingRIGHT.31.Oillinetopilotoilinlet.32.PilotoillineforstickOUT.33.PilotoillineforswingLEFT.

PILOTCONTROLVALVE(BoomandBucket)34.Pilotcontrolvalveforboomandbucket.35.PilotoillineforboomRAISE.36.Inletforpilotoil.37.PilotoillineforbucketOPEN(shovelDUMP).38.PilotoillineforboomLOWER.39.PilotoillineforbucketCLOSE(shovelTILTBACK).

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