Operation and maintenance manual

Section 220-0000
SM 1390 Rev 2 2-02
1
STEERING SYSTEM - Steering System Schematic
DESCRIPTION
Numbers in parentheses refer to Fig. 1.
The operation of the steering system is hydrostatic.
That is to say, there is no mechanical connection
between the steering column and the steered wheels.
Instead there are hydraulic pipes and lines between
the steering components and the steering cylinders.
Actuating pressure for steering operation is supplied
by main hydraulic pump (2).
When the steering wheel is turned, steering valve (7)
meters an oil volume proportional to the amount of
turn. This volume of oil flows through flow amplifier
valve (5) and is led to the appropriate side of
cushioned steering cylinders (8). Steering valve (7)
returns automatically to its neutral position when
turning is completed.
Emergency steering pressure is provided by a wheel
driven emergency steering pump (3) on the transmission.
A warning light (on the right hand bank of warning lights
in the cab) illuminates to warn of a fault in the steering
system supply pressure. If the light illuminates, stop the
vehicle and investigate the cause.
Note: The steering system warning light illuminates
when the ignition is turned on and should go out when
the engine starts.
A brief description of the individual components used
in the steering system are listed below. Detailed
service and operating instructions can be found in the
relevant component sections of this manual.
Hydraulic Tank (1)
Refer to Section 230-0040, HYDRAULIC TANK.
The hydraulic tank is the common reservoir for the
steering, braking and body hoist systems. It is
mounted off the frame and fender bracket at the rear
right hand side of the tractor.
Integral with the hydraulic tank assembly are the
hydraulic oil filter, oil strainer and oil level sight gauge.
Located on top of the tank assembly is the filler cap
and breather.
Main Hydraulic Pump (2)
Refer to Section 230-0050, MAIN HYDRAULIC PUMP.
Mounted off the transmission power takeoff, the main
hydraulic pump supplies hydraulic oil for operating
the steering and body hoist systems. Hydraulic oil is
drawn from the hydraulic tank (1) and pumped
through the dual manifold check valve (6) to the flow
amplifier valve (5). A priority spool within the flow
amplifier valve (5) directs oil supply from the main
hydraulic pump to the steering valve.
The maximum oil delivery rate of the pump is fixed by
the width of its respective gear set and the speed at
which the driveshaft is turned.
The pump operates in the one direction only (it is
assembled for right hand (clockwise) rotation, as
viewed from the driveshaft end).
Note: Never drive a pump in the wrong direction of
travel as pump seizure may result.
Emergency Valve (4)
Refer to Section 220-0140, EMERGENCY VALVE.
Located on the inside of the front left hand side frame
rail, the emergency valve forms part of the emergency
steering system. It is connected to the main output line
of the wheel driven Emergency Steering Pump (3)
mounted on the transmission.
Dual Manifold Check Valve (6)
Located on the inside of the front left hand side frame
rail, the dual manifold check valve is supplied by the
main hydraulic pump (2). A pilot line to the emergency
valve (4) holds off the emergency valve (4) when the
main hydraulic pump (2) is operating. The dual manifold
check valve distributes oil from the main hydraulic
pump (2) to the flow amplifier valve (5) under normal
operating conditions. If the main hydraulic pump (2)
fails, the emergency valve (4) directs oil to the flow
amplifier valve (5) via the dual manifold check valve.
Flow Amplifier Valve (5)
Refer to Section 220-0100, FLOW AMPLIFIER VALVE.
The flow amplifier valve amplifies the oil flow from the
steering valve to the steering cylinders by eight. It is
mounted on the cradle assembly at the rear of the
cab and consists of the following:
Counter pressure & anti-cavitation valve maintains a
back pressure of 5 bar (73 lbf/in²) to give improved
suction during steering and prevent cavitation in the
steering cylinder circuit.