Groundsmaster 4300--D Hydraulic SystemPage 4 -- 19
Lift Circuit: Lower Cutting Decks
A four section gear pump is coupled to the piston (trac-
tion) pump. Gear pump section (P4) supplies hydraulic
flowtotheliftcontrolmanifoldandliftcylinders.Thegear
pump takes its s uction from the hydraulic reservoir.
The lift control manifold includes three (3) electrically
operatedvalves.Solenoidv alve(S1)isusedtodirectoil
flowtoextendtheliftcylinderswhenenergizedorretract
them when de--energized. Solenoid valve (S2) allows
hydraulic flowfrom therod endof thelift cylinderswhen
energized and prevents oil passage from the lift cylin-
ders when de--energized. Proportional relief valve
(PRV) is used to control the operation of the manifold
logiccartridge(LC)andalsoactsasacircuitreliefvalve.
While operating the machine during conditions of not
raisingorloweringthecuttingdecks(joystickintheneu-
tral (center) position) (Fig. 19), all of the lift manifold
valves(S1,S2andPRV)arede--energized.Thede--en-
ergizedreliefvalve(PRV)allowshydraulicflowtoreturn
to tank through the manifold. This flow causes a pres-
suredifferentialthatshifts thelogiccartridge(LC) which
allows pump flow to bypass the lift cylinders. Flow re-
turns to the oil filter and then to the hydraulic reservoir.
NOTE: When the mow speed limiter is in the transport
position, the cutting decks will not lower.
Lower Cutting Decks (Fig. 18)
When the joystick is moved to the lower position, the
controllerenergizesalloftheliftmanifoldvalves(S1,S2
and PRV). The energized relief valve (PRV) prevents
flow through the valve which r eturns logic cartridge LC
to the unshifted position. With lift manifold cartridges in
this position, pump flow is directed to the barrel end of
allliftcylinderstoextendthecylindersandlowerthecut-
ting decks.Fixed orifices in thelift control manifold(C2,
C4,C 6andC8)controltheloweringspeedofthecutting
decks by providing a restriction for the return flow from
the lift cylinders.
While the cutting decks are being lowered, the propor-
tional relief valve (PRV) has a secondary function as a
circuit relief to limit lift circuit pressure to 2000 PSI (138
bar). Lift circuitpressurecan be monitored at lift control
manifold port G4.
When the joystick is returned to the neutral (center)
position, all of the lift manifold valves (S1, S2 and PRV)
arede--energized.Thede--energizedreliefvalve(PRV)
allows hydraulic flow to return to tank through the man-
ifold. This flow causes a pressure differential that shifts
the logic cartridge (LC) which allows pump flow to by-
pass thelift cylinders.All liftcylindersand cuttingdecks
are held in position by de--energized v alve S2.
Counterbalance
Once the cutting decks are fully lowered, the lift control
manifold proportionalrelief valve(PRV) maintainsback
pressure (counterbalance) on the deck lift cylinders.
This counterbalance pressure transfers cutting deck
weighttothemachineto improvetraction.Asetofwires
locatedbehindthecontrolarmaccesscoverallowcoun-
terbalance pressure to be adjusted to one of three set-
tings.
Apressuretransducerlocatedintheforwardtractionhy-
draulictubeisusedbythecontrollerasaninputtodeter-
mine traction circuit pressure. Based on transducer
inputandmachine counterbalancesetting,anelectrical
output from the controller is p rovided to the lift control
manifoldproportionalreliefvalve(PRV)tovarycounter-
balance pressure. As traction pressure increases (e.g.
climbing a hill) the counterbalance pressure also in-
creases toincrease theweight onthe tires andimprove
traction.
Figure 19
LIFT
CONTROL
MANIFOLD
FROM
PUMP P4
TO OIL
FILTER
DE--ENERGIZED
S1, S2 AND PRV
LC SHIFTED
LIFT CIRCUIT: NOT RAISING OR LOWERING
Hydraulic
System
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