Steering Circuit - Toro Greensmaster 3120 Service Manual

Steering Circuit

Right Turn
Left Turn
Hydraulic System: Hydraulic Flow Diagrams
The tandem gear pump is directly coupled to the piston (traction) pump. The rear
gear pump section (P2) supplies hydraulic flow for the steering circuit (priority
flow), for raising and lowering the cutting units and for the traction charge
circuit. The gear pump takes its suction from the hydraulic tank. Maximum
circuit pressure of 7,998 kPa (1160 PSI) is limited by the relief valve located in
the steering unit.
With the steering wheel in the neutral (not turning) position and the engine
running, the spool valve in the steering unit is in the center position; refer to
Figure 24. Flow enters the steering unit at port (P) and goes through the spool
valve, by-passing the steering cylinder. Flow leaves the control unit out port (E)
to be available for the raise/lower and traction charge circuits.
When a right turn is made with the engine running, the turning of the steering
wheel positions the spool valve in the steering unit so that flow goes through the
bottom of the spool; refer to
(P) goes through the spool and is routed to two places. First, most of the flow
through the valve is by-passed out steering unit port (E) and is available for
raising and lowering the cutting units and for the traction charge circuit. Second,
the remainder of the flow is drawn through the steering valve rotary meter and
out steering unit port (R). Pressure extends the steering cylinder for a right turn.
The rotary meter ensures that the fluid flow to the cylinder is proportional to the
amount of turning on the steering wheel. Fluid leaving the cylinder flows back
through the spool valve then out steering unit port (T) and then to the traction
charge circuit. When turning is complete, the steering unit returns to the neutral
position.
When a left turn is made with the engine running, the turning of the steering
wheel positions the spool valve in the steering unit so that flow goes through
the top of the spool; refer to
(P) goes through the spool and is routed to two places. First, most of the flow
through the valve is by-passed out steering unit port (E) and is available for
raising and lowering the cutting units and for the traction charge circuit. Second,
the remainder of the flow is drawn through the steering valve rotary meter and
out steering unit port (L). Pressure retracts the cylinder for a left turn. The rotary
meter ensures that the fluid flow to the cylinder is proportional to the amount of
turning on the steering wheel. Fluid leaving the cylinder flows back through the
spool valve then out steering unit port (T) and then to the traction charge circuit.
When turning is complete, the steering unit returns to the neutral position.
Figure 24. Flow entering the steering unit at port
Figure 24). Flow entering the steering unit at port
Page 4–24 Greensmaster 3120
17230SL Rev C