Lift Circuit - Toro Groundsmaster 3280-D Service Manual

Lift Circuit

The hydrostatic transmission charge pump supplies
charge oil for the closed loop traction circuit in addition
to supplying flow for the steering circuit and the cutting
deck (or implement) lift circuit. The charge pump takes
its suction through a filter from the reservoir (front axle).
Pump output flows to the steering control valve before
reaching the lift valve so the steering circuit has priority.
Lift circuit pressure is limited from 700 to 1000 PSI by the
implement relief valve located in the hydrostat.
During conditions of not steering or raising/lowering the
cutting deck (or implement), flow from the charge pump
goes to the lift control valve and is by--passed through
the oil cooler and then to the reservoir (front axle).
Raise Cutting Deck (Or Implement) (Fig. 9)
When the cutting deck (or implement) is to be raised, the
control valve spool is positioned back and flow is di-
rected out the B port of the control valve to the cylinder
(upper) end of the lift cylinders. Hydraulic pressure
against the cylinder pistons extends the lift cylinders. At
the same time, the pistons push the hydraulic fluid in the
lower portion of the lift cylinders out and to the reservoir
(front axle). The extending lift cylinders cause the cut-
ting deck (or implement) to raise.
When the control valve lever is released, spring action
returns the lift control spool to the center position and
by--passes flow back to the reservoir (front axle). Lift cyl-
inder movement is stopped.
LIFT CIRCUIT (LOWER)
Groundsmaster 3280--D/3320
Lower Cutting Deck (Or Implement) (Fig. 10)
When the cutting deck (or implement) is to be lowered,
the control valve spool is moved forward causing the pi-
lot valve to shift. This shifted valve allows a return path
from the lift cylinders to the reservoir (front axle) (Fig.
10). The weight of the cutting deck (or implement)
causes the cylinders to retract thus lowering the cutting
deck (or implement). As the cylinders retract, the pistons
draw hydraulic fluid from the reservoir (front axle) into
the lower portion of the lift cylinders.
When the control valve lever is released, the lift control
spool returns to the center position and causes the pilot
valve to shift. Oil flow by--passes to the reservoir (front
axle) and lift cylinder movement is stopped.
Counterbalance
An adjustable counterbalance valve allows cutting unit
weight transfer to the machine to improve traction. On
early production machines, the counterbalance valve is
incorporated in the lift control valve. Later production
machines have a separate counterbalance manifold.
Changes in traction conditions (e.g. moving up an in-
cline) will cause a valve shift to slightly lift or lower the
cutting deck to alter weight transfer. Counterbalance
pressure settings are dependant on the cutting deck
used on a machine. Refer to Traction Unit Operator's
Manual for counterbalance pressure recommenda-
tions.
Figure 10
Rev. A
Page 5 - - 11 Hydraulic System