Service Manual

Afoursectiongearpumpiscoupledtothepiston(traction)pump.Thefourth
gearpumpsection(farthestfromthepistonpump)supplieshydraulicowtothe
steeringcircuit,theenginecoolingfancircuitandthetractionchargecircuit.
Priorityhydraulicowfromthisgearpumpsectionisprovidedtothesteering
circuitbythepressurecompensatorvalve(EC)locatedinthecombination
manifold.
Note:Thehydraulicschematicsymbolforthepressurecompensatorvalve(EC)
appearstobeatwo(2)positionvalve.Inoperation,thisvalvewilldirectthegear
pumpsectionowtothesteeringcircuitasprioritydependingonsteeringinput.
Theremainderofthegearpumpsectionowwillbedirectedtothechargeand
enginecoolingfancircuits.Ifthereisnosteeringinput,thecompensatorvalve
(EC)directsallgearpumpsectionowtothechargeandenginecoolingfan
circuits.
Thecombinationmanifoldcontrolstheoperationofthesteeringcontrolvalve,
theenginecoolingfanmotorandthecuttingdeckliftcylinders.Thepressure
compensatorvalve(EC)inthemanifoldcontrolstheoilowtothesteering
controlvalvewhichisaclosedcenter,loadsensingvalve.Thesteeringcontrol
valvesensestheoilowthatisneededforsteeringandthecompensatorvalve
(EC)willsupplythecorrectamount.Oilownotneededforthesteeringcircuitis
providedtotheenginecoolingfanmotorandthentothetractionchargecircuit.
Withthesteeringwheelintheneutral,atrestpositionandtheenginerunning,
hydraulicoilfromthenalgearpumpsectionentersthecombinationmanifold
portP4,owsthroughthepressurecompensatorvalve(EC)andtothesteering
controlvalvewhereitdeadheadsatthesteeringcontrolspool.Oilisalsosent
tobothendsofthecompensatorvalve(EC)spool.Ononeendofthespool,oil
isdirectedtothesteeringreliefvalve(RV1)andalsoisdirectedthroughthe
OR1oriceandouttheLSmanifoldporttothesteeringcontrolvalve.Thisow
providessteeringloadsensepressureandisdirectedthroughasmallpassage
inthesteeringcontrolvalvespoolandsleevebeforereturningtothehydraulic
reservoir.Whilethisloadsensepressureisreturningtothereservoir,the
compensatorvalve(EC)spoolshiftstodirectpumpowtotheenginecoolingfan
motorcircuitandthentothetractionchargecircuit.Withoutsteeringinput,nooil
isowingthroughthesteeringcontrolvalvetothesteeringcylinder.
RightTurn
Whenarightturnismadewiththeenginerunning,theturningofthesteering
wheelpositionsthesteeringcontrolvalvespoolsothattheloadsenseow
isblockedoff.Withoutloadsenseow,pressuresontheendsofmanifold
compensatorvalve(EC)starttoequalizecausing(EC)tomovetowardits
neutralpositionwhichallowstheneededoilowtothesteeringcontrolvalve.Oil
isroutedoutmanifoldportCF ,intosteeringvalveportP ,throughthesteering
controlspool,isdrawnthroughtherotarymetersectionandouttheRportto
thesteeringcylinder.Pressureextendsthesteeringcylinderforarightturn.
Therotarymeterensuresthattheoilowtothecylinderisproportionaltothe
amountoftheturningonthesteeringwheel.Fluidleavingthecylinderows
backthroughthesteeringvalveLport,thespoolvalve,outtheTportandthen
returnstothehydraulicreservoir.
Thesteeringcontrolvalvereturnstotheneutralpositionwhenturningis
completed.
Groundsmaster
®
4100-D&4110-D
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HydraulicSystem:HydraulicFlowDiagrams
13203SLRevE