211-02 Power Steering: Description And Operation (page 6 of 7)

 
The power steering pumps used on the three engine variants are basically the same pump with different connection 
fitments, therefore they are not interchangeable. The pump is a positive displacement, vane type pump which supplies 
hydraulic pressure to the steering gear valve unit. The pump is driven by a Poly Vee belt from the crankshaft pulley and 
output from the pump increases proportionally with engine speed. A self-adjusting tensioner is fitted to maintain the 
correct tension on the belt. 
 
The pump has an internal pressure relief valve which also incorporates a flow control valve. The pressure relief valve 
limits the maximum pressure supplied to the steering gear to 114 bar (1653 lbf in

2

) ± 4 bar (58 lbf in

2

). The flow control 

valve limits the maximum flow to 8.8 l/min (1.93 gal/min) ± 0.5 l/min (0.1 gal/min) regardless of engine speed. The pump 
has a displacement of 9.6 cc/rev (0.58 in

3

/rev). 

 
A shaft runs longitudinally through the pump. One end of the shaft is fitted with a pressed-on drive pulley, the opposite 
end of the shaft is closed by a cover. The shaft runs in bearings located in the body and oil seals at each end of the shaft 
prevent leakage of hydraulic fluid. 
 
The pump contains ten vanes which rotate within a cam ring and are driven by the shaft. As the vanes rotate, the cam 
ring causes the space between the vanes to increase. This causes a depression between the vanes and fluid is drawn 
from the reservoir via the suction hose into the space between the vanes. 
 
As the shaft rotates, the inlet port is closed to the vanes which have drawn in fluid, trapping the fluid between the vanes. 
The cam ring causes the space between the vanes to reduce and consequentially compresses and pressurises the 
hydraulic fluid trapped between them. 
 
Further rotation of the shaft moves the vanes to the outlet port. As the vanes pass the port plate the pressurised fluid 
passes from the pump outlet port into the pressure hose to the steering gear. 
 
The pressurised fluid is subject to control by the flow control and pressure relief valve. The flow control valve maintains a 
constant flow of fluid supplied to the steering gear irrespective of engine speed variations. The pressure relief valve 
controls the pressure on the output side of the pump. A metering orifice is included in the discharge port of the pump. If 
the pressure in the orifice reaches a predetermined level, a spring loaded ball in the center of the flow control valve is 
lifted from its seat and allows pressurised fluid to recirculate within the pump. 
 
The pressure relief valve will operate if the discharge from the pump is restricted, i.e.; steering held on full lock. If the 
output from the pump is blocked, all output is recirculated through the pump. In this condition, as no fresh fluid is drawn 
into the pump from the reservoir, the fluid temperature inside the pump will increase rapidly. Consequentially, periods of 
operation of the steering gear on full lock should be kept to a minimum to prevent overheating of the pump and the fluid 
within it. 
 

RESERVOIR 

Item  Part Number  Description 

1

 -

4.0L V6

2

 -

4.4L V8

3

 -

TdV6