Rover DEFENDER 300Tdi, Workshop Manual

Page: 218 / 450

STEERING
5 DESCRIPTION AND OPERATION
Pump and regulator valve operation
The pump which is belt driven from the engine is an
eccentric roller type and also houses the pressure
regulator and flow control valve. The pressure is
controlled by a spring loaded ball valve (3) which is
housed inside the flow control valve piston (4).
No demand for assistance High flow through box -
Low pressure
With no demand for assistance the rotary valve in the
steering box acts as a pressure relief valve, allowing
fluid (A) to flow freely through the steering box and
back to the reservoir and pump inlet (B).
No demand for assistance
1. Reservoir
2. Pump
3. Pressure control ball valve and spring
4. Flow control valve and spring
5. Press fit plug (ball bearing)
6. Restrictor
The ball plug (5) is pressed into the valve (4)
during manufacture and determines the opening
pressure of pressure relief valve (3).
No flow, through box - High pressure
When the steering is turned, the rotary valve
effectively stops all fluid flow through the steering box,
thus causing an increase in pressure (A). This
increase in pressure is felt in the flow control valve
spring chamber where, at a pre-determined pressure
the relief valve (3) will open and allow the pressure to
escape. The fall in pressure in the flow control spring
chamber, allows the flow control valve to move to the
right, which in turn allows pump output (A) to escape
directly into the pump inlet (B).
Assistance demanded
As soon as the steering wheel is released after
making a turn, the system reverts to the condition
seen in J6292 and the road wheels are returned to the
straight ahead position by the mechanical steering
geometry.
In the event of any hydraulic failure, steering control,
though heavy, will be maintained through the
mechanical components in the steering box.