6-12 4203780 First Edition
HYDRAULICS
6
Theory of Operation and
Diagnostic Information
Steering Circuit Schematic and
Theory of Operation
System Conditions:
• Engine running
• Steering wheel turned to the right or left (right turn
shown)
Oil Supply to Steering Valve
Hydraulic oil is drawn from the hydraulic oil tank by
section 1 of the gear pump assembly. Before entering the
gear pump assembly, the inlet oil is filtered by a
100-mesh screen to remove any debris.
Operating-pressure oil from section 1 of the four-section
gear pump is routed to port “P” of the control valve, flows
through the 4.5-gpm priority valve and out port “ST” to
the steering valve.
The priority valve will supply oil flow to the steering valve
before allowing oil flow to the lift valve, to ensure
maximum steering control at any engine rpm range.
Steering Circuit
Operating-pressure oil enters the steering unit at “IN”
port, and is routed to the pilot line of the 1450-psi relief
valve, against the check valve, and to the steering valve.
With the steering wheel turned to the right, the steering
valve is moved, allowing oil to flow through the valve to
the gerotor metering section. Oil is then routed through
port “RT” of the steering unit to the steering cylinder,
moving the rear wheels in the desired direction.
Oil from the opposite end of the steering cylinder flows
back into the steering unit through port “LT” and back
through the steering valve, exiting through the steering
unit “OUT” port. Oil exiting the steering unit then flows
through the charge filter, and supplies charge-pressure
oil to the traction pump and other systems.
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