The principle of operation of the power steering (Freelander 2)

Schematic representation of a typical fixed displacement pump:

Pos.	Spare part number	Name
1	-	Tank
2	-	Working fluid cooler
3	-	Valve block
4	-	Steering rack and pinion
5	-	Flow control/pressure relief - return line
6	-	Flow regulator/pressure 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 via the low-pressure suction line. The fluid passes through the pump and exits under pressure from the outlet. The high-pressure hose directs the fluid under pressure to the steering gear valve block.

If the steering wheel is not turned, the system capacity is almost not reduced and the pump feed pressure is low. Minimal pressure is supplied to each side of the piston in the hydraulic cylinder through the valve block and all the fluid from the power steering pump returns to the reservoir through the cooler.

When the steering wheel is turned in any direction, the return flow of fluid to the reservoir is restricted by the valve block, increasing the pump feed pressure. The 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 the fluid cooler to the reservoir. The fluid cooler reduces the temperature of the fluid, improving the performance of the fluid. The cooler also extends the life of the hoses and seals in the system.

(The original text can be found at: LRman.ru)