Steering Circuit - Toro 30821 Service Manual

Steering Circuit

The gear pump (P2) is directly coupled to the hydrostat.
It supplies hydraulic pressure to the power steering
valve for turning the rear wheel and maintaining 100 to
150 PSI (6.9 to 10.0 Bar) to the low pressure side of the
traction circuit. The pump takes its suction from the hy-
draulic reservoir.
With the steering wheel in the neutral position (rear
wheel positioned straight ahead), the engine running,
and the spool valve in the center position, flow enters the
steering control valve at the IN port and goes through the
spool valve, by- passing the rotary meter (V1) and steer-
ing cylinder. Flow leaves the control valve through the
AUX port to the hydrostat to be available for the lift circuit
and then to the hydrostat (charge).
Right Turn
When a right turn is made with the engine running, the
turning of the steering wheel positions the spool valve so
that flow goes through the bottom of the spool. Flow en-
tering the steering control valve at the IN port goes
through the spool and is routed to two places. First, most
of the flow through the valve is by- passed out the AUX
port back through the 2- spool valve to the hydrostat.
Second, the remainder of the flow is drawn through the
rotary meter (V1) and out port (R). Pressure retracts the
piston for a right turn. The rotary meter (V1) ensures that
Groundsmaster 3500- D
the oil flow to the cylinder is proportional to the amount
of the turning on the steering wheel. Fluid leaving the
cylinder flows back through the spool valve then through
the OUT port and to the hydrostat.
The steering control valve returns to the neutral position
when turning is complete.
Left Turn
When a left turn is made with the engine running, the
turning of the steering wheel positions the spool valve so
that flow goes through the top of the spool. Flow entering
the steering control valve at the IN port goes through the
spool and is routed to two places. As in a right turn, most
of the flow through the valve is by- passed out the AUX
port back through the 2- spool valve to the hydrostat.
Also like a right turn, the remainder of the flow is drawn
through rotary meter (V1) but goes out port (L). Pressure
extends the piston for a left turn. The rotary meter (V1)
ensures that the oil flow to the cylinder is proportional to
the amount of the turning on the steering wheel. Fluid
leaving the cylinder flows back through the spool valve
then through the OUT port and to the hydrostat.
The steering control valve returns to the neutral position
when turning is complete.
Page 4 - 23 Hydraulic System (Rev. G)