Service Manual

Groundsmaster 4300--D Hydraulic SystemPage 4 -- 17
Lift Circuit: Raise Cutting Decks
A four section gear pump is coupled to the piston (trac-
tion) pump. Gear pump section (P4) supplies hydraulic
flowtotheliftcontrolmanifoldandliftcylinders.The gear
pump takes its suction from the hydraulic reservoir.
The lift control manifold includes three (3) electrically
operated valves. Solenoidvalve (S1) is used to direct oil
flowtoextend the liftcylinderswhen energized orretract
them when de--energized. Solenoid valve (S2) allows
hydraulic flow from the rod end of the lift cylinders when
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)and also actsas acircuit relief valve.
While operating the machine during conditions of not
raising or lowering the cutting decks (joystick in the neu-
tral (center) position) (Fig. 17), all of the lift manifold
valves (S1, S2 and PRV)are de--energized. The de--en-
ergized r elief valve (PRV)allows hydraulic flow toreturn
to tank through the manifold. This flow c auses a pres-
sure differentialthat shifts the logic cartridge (LC) which
allows pump flow to bypass the lift cylinders. Flow re-
turns to the oil filter and then to the hydraulic reservoir.
Raise Cutting Decks (Fig. 16)
Whenthejoystick ismovedtothe raiseposition,thecon-
troller energizes the proportional relief valve (PRV).The
energized relief valve (PRV) prevents flow through the
valve which returns logic cartridge LC to the unshifted
position. With lift manifold cartridges in this position,
pump flow is directed to the rod end of all lift cylinders to
retract the cylinders and raise all cutting decks. Flow to
the lift cylinders bypasses the control manifold fixed ori-
fices to prevent flow restriction during deck raising.
Whilethe cutting decks are being raised, the proportion-
al relief valve (PRV) has a s econdary function as a cir-
cuit relief to limit lift circuit pressure to 2000 PSI (138
bar). Lift circuit pressure can be monitored at lift control
manifold port G4.
When the joystick is returned to the neutral (center)
position, the proportional relief valve (PRV) is de--ener-
gized. The de--energized relief valve (PRV) allows hy-
draulic flow to return to tank through the manifold. This
flow causes a pressure differential that shifts the logic
cartridge (LC) which allows pump flow to bypass the lift
cylinders. All lift cylinders and cutting decks are held in
the raised position by de--energized valve S2.
Figure 17
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