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DESCRIPTION
Numbers in parentheses refer to Figs. 2 through 6.
The steering system is of the accumulator type which
provides uniform steering, regardless of engine speed,
and provides a limited amount of reserve steering
pressure should the engine stall.
A brief description of the individual components used
in the steering system are listed below. Detailed
service and operating instructions for the individual
components can be found in their relative component
sections in this manual.
Steering and Brake Control Tank (1)
Refer to Section 220-0040, STEERING AND BRAKE
CONTROL TANK.
The steering and brake control tank is the common oil
reservoir for the steering system and the brake control
system. It is mounted off the LH frame rail beside the
main hydraulic tank.
An Oil Level Switch (9), mounted at the rear of the
tank, is used to indicate low oil level in the tank. The
switch terminal is wired to a warning light on the right
hand dash panel.
Steering Pump (2)
Refer to Section 220-0050, STEERING PUMP.
The steering pump is an axial piston, variable
displacement (adjustable) pump, capable of high
pressure operation. Mounted off the transmission
power takeoff the steering pump is the common
pressure supply to both the steering and brake control
systems. Output is controlled to meet system
requirements at any given time.
A compensator valve assembly regulates system
pressure at 159 bar (2 300 lbf/in
The steering pump is assembled for right hand (clockwise)
rotation, as viewed from the driveshaft end.
Note: Never drive a pump in the wrong direction of
rotation, as pump seizure may result.
Accumulator (3)
Refer to Section 220-0080, ACCUMULATOR.
The accumulator is of the piston type and is
precharged with Nitrogen to 55 bar (800 lbf/in
SM 1591 12-98
STEERING SYSTEM - Steering System Schematic
2
).
2
).
Mounted off the frame at the rear of the steering and
brake control tank, the accumulator assembly consists
of a charging valve, end cap, cylinder and piston.
The charging valve is equipped with a locking feature
which, when opened, will allow the precharge to be
checked or the accumulator charged. The piston acts
as a separator dividing the cylinder into two sections.
The section nearest the charging valve contains the
nitrogen precharge. The other section receives the
hydraulic oil from the steering pump, via accumulator
valve (4).
Accumulator Valve (4)
Refer to Section 220-0130, ACCUMULATOR VALVE.
Note: The relief valve cartridge can be replaced only
as an assembly.
Incorporated in this assembly are three valves; a
check valve, accumulator two-way valve and a system
pressure protection valve.
An accumulator two-way valve is located in the centre
portion of the assembly. In the operating position,
engine running and two-way valve energized, this
valve allows the accumulator to retain its pressure. In
its non-operating position, engine shutdown and two-
way valve de-energized, a controlled bleed-down of
the accumulator pressure to the steering and brake
control tank occurs. This bleed-down takes 3 to 5
minutes.
A relief valve cartridge, at the lower portion of the
assembly, is preset to 207 bar (3 000 lbf/in
seated. This valve acts as a backup in the event of a
malfunction of the steering pump compensator valve.
Should the compensator valve allow steering system
pressure to exceed the preset pressure of the relief
valve cartridge, valve will open and relieve excess oil
pressure to the steering and brake control tank.
Steering Valve (5)
Refer to Section 220-0090, STEERING VALVE.
The steering valve is mounted to the cab firewall and
is connected to the steering column, and controls
hydraulic flow in the steering system. The steering
valve is a closed centre orbitrol type valve. Closed
centre means that the valve does not have any flow
through it when it is in the neutral or no steering
position.
Section 220-0000
2
) and
1
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