Power steering distributor valve

Power steering distributor valve

The power steering pump is driven by the engine by a belt, and can supply a feed pressure varying from 3.5 bar in the "neutral" position to a maximum of 85 bar in the "full lock" position. The power-assisted steering assembly is similar to a mechanical steering gear, except for the following differences: a. the steering gear contains an actuating cylinder (2) in which a double-effect piston (1) slides, joined to the rack; b. in the seating of the worm screw, there is a distributor valve (3) with its pipes. It is controlled by a torsion device (4), located at the end of the worm screw. Depending on the torsion transmitted by the steering wheel to the device, the fluid is sent from the pump to the reservoir, or to one of the two chambers A or B of the actuating cylinder. The force generated by the fluid pressure on the lateral surface of the piston causes the piston, and hence the rack, to move.

Longitudinal section of power-assisted rack and pinion steering gear

Checking operation

Check the steering wheel's rolling torque with the car stopped and the engine running. The torque should be between 0.6 daN with the engine idling and 0.75 daN with the engine at maximum rpm. If it exceeds these values, check the system pressure with the wheels at full lock. To do this, fit a pressure gauge, with a T connector, on the pressurized fluid delivery pipe to the power steering gear (from the pump) and turn the steering wheel to full lock on one side. When the steering wheel is forced to rotate further, the pressure reading on the pressure gauge should rise to about 85 bar. If this does not happen, check whether there is a fault in the power steering fluid pump or distributor valve. The above check should be conducted with the engine running at 2000 - 4000 rpm.

NOTE Under no circumstances should the power steering assembly and vane pump be dismantled into their components; instead they should be returned to the manufacturer for overhaul.

Checking fluid level: the fluid level should be checked with the engine running, and it should be topped up as necessary.