Steering Circuit - Toro Groundsmaster 3500 30807 Service Manual

Steering Circuit

The gear pump (P2) is directly coupled to the hydrostat
through gear pump (P1) and driven by the engine. It sup-
plies hydraulic pressure for operating the power steer-
ing system, raising and lowering the cutting units,
operating the sidewinder unit, and maintaining 100 to
150 PSI (6.9 to 10.0 bar) to the low pressure side of the
closed loop traction circuit (charge pressure). The pump
takes its suction directly from the hydraulic tank.
With the steering wheel in the neutral position, the en-
gine running, and the lift/sidewinder spool valve in the
center position, flow enters the steering control valve at
the P port and goes through the valve, by−passing the
rotary meter (V1) and steering cylinder. Flow leaves the
steering control valve through the E port, passes
through the lift/sidewinder valve, hydraulic manifold, hy-
drostat and charge relief valve, and continues on to the
gear pump inlet and hydraulic tank.
Right Turn
When a right turn is made with the engine running, the
turning of the steering wheel positions the steering con-
trol spool valve so that flow goes through the bottom of
the spool. Flow entering the steering control valve at the
P port goes through the spool and is routed to two
places. First, most of the flow through the steering con-
trol valve is by−passed out the E port back through the
lift/sidewinder valve, hydraulic manifold, hydrostat and
charge relief valve, and continues on to the gear pump
inlet and hydraulic tank. 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 the fluid flow to the cylin-
der is proportional to the amount of steering wheel rota-
Groundsmaster 3500
tion. Fluid leaving the cylinder flows back through the
steering control spool valve and through the T port. Re-
turn flow passes through the hydraulic manifold, hydro-
stat and charge relief valve, and continues on to the gear
pump inlet and hydraulic tank.
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 steering con-
trol spool valve so that flow goes through the top of the
spool. Flow entering the steering control valve at the P
port goes through the spool and is routed to two places.
Most of the flow through the steering control valve is by−
passed out the E port back through the lift/sidewinder
valve, hydraulic manifold, hydrostat and charge relief
valve, and continues on to the gear pump inlet and hy-
draulic tank (as in a right turn). The remainder of the flow
is drawn through rotary meter (V1) but during a left turn
the flow goes out port (L). Pressure extends the piston
for a left turn. The rotary meter (V1) ensures that the fluid
flow to the cylinder is proportional to the amount of steer-
ing wheel rotation. Fluid leaving the cylinder flows back
through the spool valve then through the T port. Return
flow passes through the hydraulic manifold, hydrostat
and charge relief valve, and continues on to the gear
pump inlet and hydraulic tank.
The steering control valve returns to the neutral position
when turning is complete.
Page 5 − 29 Hydraulic System