Toro Reelmaster 3550-D Service Manual page 59

Steering Circuit
The tandem gear pump is directly coupled to the vari-
able displacement piston pump/hydrostat which is belt
driven by the engine. The rear section of the tandem
gear pump (P2) supplies hydraulic flow for the steering
circuit, for raising and lowering the cutting units and for
the traction charge circuit. The gear pump takes its suc-
tion from the hydraulic tank. Maximum steering circuit
pressure of 1000 PSI (69 bar) is limited by the relief
valve located in the power steering valve.
With the engine running and the steering control valve
in the centered position (steering wheel not being
turned), hydraulic flow enters the steering control valve
at the P port and goes through the control valve, by−
passing the rotary meter and steering cylinder. On Reel-
master 3550−D machine, the steering circuit comes
before the lift circuit. Flow leaves the steering control
valve through the E port to supply the lift circuit and then
the traction charge circuit. On Reelmaster 3555−D and
3575−D machines, the steering circuit comes after the
lift circuit. Flow leaves the steering control valve at the
T port to supply the traction charge circuit.
Right Turn
When a right turn is made with the engine running, the
turning of the steering wheel positions the control valve
so that flow goes through the bottom of the valve. Gear
pump flow entering the steering control valve at the P
port goes through the valve and is routed to two places.
First, most of the flow is by−passed through the steering
valve and exits out the E port (Reelmaster 3550−D) or
T port (Reelmaster 3555−D and 3575−D). Second, the
remainder of the flow is drawn through the rotary meter
in the steering control valve and out port R to the steer-
ing cylinder. Flow retracts the steering cylinder for a right
turn. The rotary meter ensures that the oil flow to the
steering cylinder is proportional to the amount of the
steering wheel rotation. Fluid leaving the steering cylin-
der flows back through the steering control valve then
through the T port and on to the traction charge circuit.
The steering control valve returns to the neutral position
when turning is complete.
Reelmaster 3550−D/3555−D/3575−D
Left Turn
When a left turn is made with the engine running, the
turning of the steering wheel positions the steering con-
trol valve so that flow goes through the top of the valve.
Gear pump flow entering the steering control valve at
the P port goes through the spool and is routed to two
places. As in a right turn, most of the flow is by−passed
through the steering valve and exits out the E port (Reel-
master 3550−D) or T port (Reelmaster 3555−D and
3575−D). Also like a right turn, the remainder of the flow
is drawn through the rotary meter in the steering control
valve but goes out port L to the steering cylinder. Flow
extends the steering cylinder for a left turn. The rotary
meter ensures that the oil flow to the cylinder is propor-
tional to the amount of the turning on the steering wheel.
Fluid leaving the steering cylinder flows back through
the steering control valve then through the T port and on
to the traction charge circuit.
The steering control valve returns to the neutral position
when turning is complete.
Page 4 − 27 Hydraulic System