Service Manual

LowertheCuttingDecks(continued)
directedtothebarrelendofallliftcylinderstoextendthecylindersandlowerthe
cuttingdecks.The4xedoricesintheliftcontrolmanifold(C2,C4,C6,and
C8)controltheloweringspeedofthecuttingdecksbyprovidingarestrictionfor
thereturnowfromtheliftcylinders.
Whilethecuttingdecksarebeinglowered,theproportionalreliefvalve(PRV)
hasasecondaryfunctionasacircuitrelieftolimitliftcylindercircuitpressure
to13,800kPa(2,000psi).Theliftcylindercircuitpressurecanbemonitoredat
liftcontrolmanifoldportG4.
Whenthecuttingdecksarefullylowered,theliftmanifoldvalves(S1andPRV)
arede-energized(Figure37).Thede-energizedreliefvalve(PRV)allows
hydraulicowtoreturntotankthroughthemanifold.Thisowthroughthe
pressurereliefvalvecausesapressuredifferentialthatshiftsthelogiccartridge
(LC)whichallowsthemajoritypumpowtobypasstheliftcylinders.Thelift
manifoldvalveS2remainsenergizedwhenthecuttingunitsarefullyloweredto
allowuidowtoandfromtheliftcylinders.Thebidirectionalowisnecessary
forpropercuttingdeckcounterbalance/oatoperation.
Counterbalance/Float
Oncethecuttingdecksarefullylowered,theliftcontrolmanifoldsolenoid
valve(S2)remainsenergizedandtheproportionalreliefvalve(PRV)isusedto
maintainanamountofpressure(counterbalance)ontherodendsofthedeck
liftcylinders(Figure37).Thiscounterbalancepressuretransferscuttingdeck
weighttothemachinetoimprovethetraction.
Apressuretransducerlocatedintheforwardtractionhydraulictubeisusedby
thecontrollerasaninputtodeterminetractioncircuitpressure.Basedonthe
transducerinputandthemachinecounterbalancesetting,anelectricaloutput
fromthecontrollerisprovidedtotheliftcontrolmanifoldproportionalreliefvalve
(PRV)tovarythecounterbalancepressure.Asthetractionpressureincreases
(e.g.,climbingahill)thecounterbalancepressurealsoincreasestoincreasethe
weightonthetiresandimprovetraction.Thecounterbalancesettingcanbe
adjustedtoLOW,MEDIUM,andHIGHviatheInfoCenterdisplay;refertoInfoCenter
Display(page5–7)ortheTractionUnitOperator'sManual.
HydraulicSystem:HydraulicFlowDiagrams
Page4–28
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