Service Manual

Rev. A
Groundsmaster 7200/7210 Hydraulic SystemPage 4 - 13
Lift Circuit (Raise)
A single section gear pump is directly coupled to the
transmission which is driven by the engine. This gear
pump supplies hydraulic flow for raising and lowering
the cutting deck (or implement). The pump takes its suc-
tion from the hydraulic tank.
During conditions of not raising or lowering the cutting
deck ( or implement), flow from the gear pump by- pass-
es the lift circuit and is routed directly to the oil cooler and
then to the transmission. Flow then returns to the hy-
draulic tank.
NOTE: The engine must be running to allow the cutting
deck (or implement) to be raised.
Manual Lift Control (Serial Number Below
313000000)
Machines with serial numbers below 313000000 have
a manual lift control valve that uses a lever to raise the
cutting deck ( or implement).
When the lift control lever is moved to the RAISE posi-
tion, the lift control valve spool is shifted. This shifted
spool allows hydraulic flow from the gear pump to the
barrel end of the lift cylinder. At the same time, the pilot
check valve in the lift control valve is unseated. The lift
cylinder extends, causing the cutting deck (or imple-
ment) to raise. The fluid displaced from the rod end of
the lift cylinder is routed past the unseated pilot check
valve, to the oil cooler, transmission and then to the hy-
draulic tank. An orifice fitting at the barrel end of the lift
cylinder controls the extending speed of the lift cylinder
while raising the cutting deck (or implement).
Load on the lift cylinder causes lift circuit pressure to in-
crease. If lift circuit pressure reaches implement relief
valve pressure (3000 PSI/207 bar), the relief valve in the
gear pump shifts to allow pump flow t o return to the hy-
draulic tank. This condition occurs in both the raise and
lower modes.
When the lift control lever is released from RAISE,
spring action returns the control valve spool to its origi-
nal, centered position, stopping lift cylinder movement.
Gear pump flow is a gain bypassed through the oil cool-
er, transmission and to the hydraulic tank. The pilot
check valve in the control valve will be reseated to lock
the lift cylinder in place.
Electrical Lift Control (Serial Number Above
313000000)
Machines with serial numbers above 313000000 have
a lift control manifold equipped with two (2) solenoid
valves for electrical control of the lift circuit. A deck lift/
lower switch on the right side traction lever is used to
raise the cutting deck (or implement).
When the top of the lift/lower switch is pressed (momen-
tary position), both solenoid valves (A/S1 and B/S2) in
the deck lift manifold are energized t o cause the valves
to shift. Energized solenoid valve B/S1 prevents gear
pump flow from bypassing the lift cylinder. Energized so-
lenoid valve A/S1 allows hydraulic flow from the gear
pump to the barrel end of the lift cylinder. The lift cylinder
extends, causing the cutting deck to raise. The fluid dis-
placed from the rod end of the lift cylinder is routed to the
oil cooler, transmission and then to the hydraulic tank.
An orifice fitting at the barrel end of the lift cylinder con-
trols the extending speed of the lift cylinder while raising
the cutting deck.
Load on the lift cylinder causes lift circuit pressure to in-
crease. If lift circuit pressure reaches implement relief
valve pressure (3000 PSI/207 bar), the relief valve in the
gear pump shifts to allow pump flow to return t o the hy-
draulic tank. This condition occurs in both the raise and
lower modes.
When the top of the lift/lower switch is released, both so-
lenoid valves (A/S1 and B/S2) in the deck lift manifold
are de- energized. De- energized solenoid valve B/S2
allows gear pump flow to bypass the lift cylinder, return-
ing to the oil cooler, transmission and then to the hydrau-
lic tank. De- energized solenoid valve A/S1 prevents
hydraulic flow to and from the lift cylinder to keep the cut-
ting deck in the raised position.
Hydraulic
System