Miller Nitro 7310 - Propel System; Auxiliary Circuit

7-MAINTENANCE
Propelsystem
Thepropelsystemcontains1electronicallycontrolledhydrostaticpumpand4electronicallycontrolledwheelmotors.
Thepropelsystemiscontrolledbyanelectronicdrivelinecontrollerwhichdeterminesthedisplacementofthehydro-
staticpumpandmotorsbasedontheoperatorscommand.Thesystemisaclosedloopcircuitwhichcombinesthe
owofhydrostaticpumpanddistributesittothefourwheelmotors.Thehydrostaticpumphasanintegralcharge
pump.Thepurposeofthechargepumpistosupplyoilintotheclosedlooppropelcircuitwhichislostduetoinefca-
ciesofthepump,motorsandprovidemake-upoilwhichisremovedbyaloopushingvalveineachmotor.
Theoilinthehydraulicreservoirispulledintothechargepumpwhereitispressurizedtoapproximately3447kPa
(500psi).Theoilisthenpushedthroughthepropelpump.Fromthereitgoesintothelowpressuresideofthe
hydrostaticpump(returnow).Fromthepropelpump(44816kPa(6500psi)orgreater)theoilispumpedaccording
todemand(theamountofdisplacementbythejoystickinthecab)tothewheeldrivemotors.Thedisplacementof
theelectronicallycontrolledwheelmotorsiscontrolledbytheelectronicdrivelinecontroller.
Thepressureinthechargepressurecircuitsisalsomonitoredwithtwoidenticalpressuretransducers.Thesepres-
suretransducerstriggerlightsandalarmsinthecabifthepressuredropsbelow1379kPa(200psi)intheirrespective
circuits.Lossinchargepressurecouldbeduetoanumberofitems:abursthose,orafailureinachargepump,a
valveorpropelpump.Propelsystemdamagecanoccurifachargepressurewarningisignored.
Extraowfromthechargepump(asitispositivedisplacement)isemptiedintothecaseofthehydrostaticpump
(propel).Asetamountofoilisalsodrainedoffthepropelcircuit(lowpressureside)toallownewoilintothesystem
(thisisaccomplishedbytheloopushingvalveineachwheelmotor).Thisallowsclean,lteredoiltoenterthesystem
viathechargepump.Theoilwhichisdrainedoffthepropelloopisthendirectedthroughaheatexchangerandthen
combineswiththehydrostaticpumpcaseowstoareturnlterlocatedinsidetheoilreservoir.
Sincetheparkbrakesarepressurereleased,aminimumof2586kPa(375psi)inrequiredintheparkingbrakecircuit
topreventtheparkbrakesfromengaging.Whenthepressuredropsbelowthisvalue,theparkingbrakeswillstartto
engage.Continuedusewiththeparkbrakelightonmaydamagethebrakesandothercomponents.Thebrakesare
protectedwithapressureswitchwhichmonitorspressureinthebrakecircuit.Theparkingbrakecircuitisfeedbythe
parkingbrake/laddervalvewhichinpartoftheauxiliaryhydrauliccircuit.
Auxiliarycircuit
Theauxiliarycircuitoperatesat20684kPa(3000psi).Thepumpsenseshowmuchowisneededfortheauxiliary
circuit.Oilisdrawnfromtheoilreservoirintothepump,whichmaintains20684kPa(3000psi)atalltimes.Theoil
owsfromthepumptothepriorityvalve.Thepriorityvalvegivesthesteeringsystempriorityoverallotherfunctions.
Onlyafterthesteeringcircuitoilneedsaresatised,isanyoilpassedthroughthepriorityvalvetotheotherfunctions:
spraypumpmotor,parkbrake,laddercylinder,liftandboomcylinders,legwidening,etc.Alloftheoilinthiscircuit
returnstoareturnlterlocatedintheoilreservoir.
HydrostaticPressure
ThehydrostatpressurecanbemonitoredonthearmresthomedisplaybyaccessingtheHydraulicsdiagnosticspage.
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