Textron JACOBSEN GP400, Technical/Repair Manual

Page: 210 / 354

6-18 4252490-Rev A
HYDRAULICS
6
Theory of Operation and
Sub-Circuit Schematics
Steering Circuit Schematic and
Theory of Operation
System Conditions:
• Engine running
• Steering wheel turned to the right or left (left turn
shown)
Oil Supply to Steering Unit
Hydraulic oil is drawn from the hydraulic oil tank by the
charge pump. Before entering the charge pump, the inlet
oil is filtered by a 10 micron filter to remove any debris.
Operating pressure oil from the charge pump is routed
through the 150–210 psi (10–15 bar) charge relief valve,
through port “V1” of the traction pump, and to port “P” of
the steering unit.
Steering Circuit
Operating pressure oil enters the steering unit at port “P,”
and is routed against the 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 “T,” to
the oil cooler, and then to the hydraulic tank.
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 to the oil cooler and then to the
hydraulic tank.
Circuit Relief
The steering system is protected by the 800 psi (55 bar)
implement relief valve. If the pressure on the pilot line of
the relief valve reaches 800 psi (55 bar), the valve will
open, dumping operating pressure oil through port “L1” of
the traction pump to the hydraulic tank.