Service Manual

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.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. 19), 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.
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
controller energizes all of the lift manifold valves (S1, S2
and 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 barrel end of
alllift cylinders toextend thecylinders andlower thecut-
ting decks. Fixed orifices in the lift control manifold (C2,
C4, C6 and C8) control the lowering speed of the cutting
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 circuit pressure can 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)
are de--energized. The de--energized relief valve (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 the lift cylinders. All lift cylinders and cutting decks
are held in position by de--energized valve S2.
Counterbalance
Once the c utting decks are fully lowered, the lift control
manifold proportional relief valve (PRV) maintains back
pressure (counterbalance) on the deck lift cylinders.
This counterbalance pressure transfers cutting deck
weight to the machine to improvetraction. A set of wires
locatedbehindthecontrolarmaccesscover allow coun-
terbalance pressure to be adjusted to one of three set-
tings.
Apressuretransducerlocatedintheforward tractionhy-
draulictubeis used bythe controller asan input to deter-
mine traction circuit pressure. Based on transducer
input and machine counterbalance setting, an electrical
output from the controller is provided to the lift control
manifold proportional relief valve (PRV)to vary counter-
balance pressure. As traction pressure increases (e.g.
climbing a hill) the counterbalance pressure also in-
creases to increase the weight on the tires and improve
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