The principle of operation of the hydraulic booster (Freelander 2)

Schematic representation of a typical fixed volume pump:

Pos.	spare part no	Name
1	-	Tank
2	-	Fluid cooler
3	-	valve block
4	-	Steering rack and pinion
5	-	Flow control/pressure relief - return line
6	-	Flow regulator/reducing valve
7	-	output port
8	-	Power steering pump
9	-	Low pressure suction line

When the engine is running, the working fluid from the reservoir enters the power steering pump through the low pressure suction line. Fluid passes through the pump and exits under pressure from the outlet. The high pressure hose directs pressurized fluid to the steering valve block.

If the steering wheel does not turn, there is little to no reduction in system flow and pump delivery pressure is low. Minimum pressure is applied to each side of the piston in the hydraulic cylinder through the valve block and all fluid from the power steering pump returns to the reservoir through the cooler.

When the steering wheel is turned in either direction, the return flow of fluid to the reservoir is restricted by the valve block, thereby increasing the pump delivery pressure. Pressurized fluid is directed by the valve block to the appropriate side of the piston in the hydraulic cylinder, making it easier to turn the steering wheel. Fluid displaced from the low pressure side of the cylinder returns through the valve block and fluid cooler to the reservoir. The fluid cooler reduces fluid temperature, improving fluid performance. The cooler also extends the life of the hoses and seals in the system.