Toro 3200, Service Manual

Page: 82 / 274

Raise and Lower Cutting Units
Raise
The gear pump (P2) is directly coupled to the hydrostat
through gear pump (P1). It supplies hydraulic pressure
for raising and lowering cutting units and maintaining
100 to 150 PSI (6.9 to 10.0 bar) to the low pressure side
of the traction circuit (charge pressure). The pump takes
its suction from the hydraulic reservoir.
During conditions of not lifting or lowering cutting units,
flow from the gear pump is by–passed through the steer-
ing control valve and solenoid valve (S2) directly to the
hydrostat and the charge relief valve(R4). Flow then re-
turns to the hydraulic reservoir.
When the cutting units are to be raised, solenoid valve
(S2) is energized and blocks flow directly to the hydros-
tat. Flow is directed to energized solenoid valve (S3),
which directs flow to de–energized solenoid valve (S4)
and the lift cylinders. Hydraulic pressure against the cyl-
inder pistons moves their shafts causing the cutting
units to raise. At the same time, the pistons push the hy-
draulic fluid out of the lift cylinders and back through so-
lenoid valves (S4 and S3) to the hydrostat. When the
solenoid valves de–energize, spring action returns the
valves to their original position and by–passes flow back
to the hydrostat stopping lift cylinder movement. The
cylinder position is locked in place since there is no com-
plete circuit of flow to and from the lift cylinders.
Lower
Circuit operation for lowering the lift cylinders is similar
to raising them. However, the solenoid valve (S3) re-
mains de–energized and in the down position and sole-
noid valve (S4) is energized and shifts down. Flow is
reversed to and from the lift cylinders, thus moving the
cutting units down.
When the cutting units are to be lowered, solenoid valve
(S2) is energized and blocks flow directly to the hydros-
tat. Flow is directed to de–energized solenoid valve
(S3), which directs flow to energized solenoid valve (S4)
and the lift cylinders. Hydraulic pressure against the cyl-
inder pistons moves their shafts causing the cutting
units to lower. At the same time, the pistons push the hy-
draulic fluid out of the lift cylinders and back through so-
lenoid valves (S4 and S3) to the hydrostat. Flow into the
flow control valve is slowed by the variable orifice to al-
low the rear cutting unit to lower after the front units.
When the solenoid valves de–energize, spring action
returns the valves to their original position and by–
passes flow back to the hydrostat stopping lift cylinder
movement.
Hydraulic System Page 5 – 10 Greensmaster 3200/3200–D