6-10 673831-Rev A
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 three-section gear
pump is routed to port “P” of the steering unit.
Steering Circuit
Operating pressure oil enters the steering unit at port “P,”
and is routed to the pilot line of the 2100 psi (145 bar)
relief valve, against the relief valve and check valve, and
to the steering valve.
With the steering wheel in the neutral (straight ahead)
position, the steering valve routes all of the operating
pressure oil out of the steering unit through port “E,”
supplying operating pressure oil to the lift valve.
3WD Option: With the steering wheel turned to the left,
the steering valve is moved, allowing oil to flow through
the valve to the gerotor metering section. Oil is then
routed through port “L” of the steering unit to the left side
of the steering cylinder, shifting the rod to the right and
moving the rear wheels in the desired direction.
Oil exiting the right side of the steering cylinder flows
back into the steering unit through port “R,” through the
steering valve, and through port “T.” Oil exiting the
steering unit is routed through the lift valve and then
returns to the hydraulic tank.
4WD Option: With the steering wheel turned to the left,
the steering valve is moved, allowing oil to flow through
the valve to the gerotor metering section. Oil is then
routed through port “L” of the steering unit to the piston
side of the steering cylinder, extending the rod, and
moving the rear wheels in the desired direction.
Oil from the rod end of the steering cylinder flows back
into the steering unit through port “R,” through the
steering valve, and through port “T.” Oil exiting the
steering unit is routed through the lift valve and then
returns to the hydraulic tank.
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