Control valve

Control valve

A. Control valve, normal position




1. Delivery pipe
2. Throttle valve
3. Pressure channel
4. Return channel
5. Control valve
6. Safety valve
7. Spring
8. Connecting channel

B. Control valve, maximum pressure




There is a control valve in the pump housing which regulates the oil quantity and maximum pressure.

When the pump starts the valve (5 in illustration A) is pushed to the left by the spring (7). The oil from the pump passes through the pressure channel (3) via the throttle valve (2) into the pressure pipe (1) and then to the steering gear.

The space to the right of the control valve is connected to the pressure pipe (1) by the connecting channel (8) and has the same pressure.

The throttle valve (2) makes the pressure on the left-hand side of the control valve piston higher than in the pressure pipe and the space to the right of the piston. When the spring pressure is overcome the piston is pushed to the right.

When rotation is sufficiently high in relation to the counter pressure the piston has been moved so much that the surplus oil can pass back to the pump side, see illustration A. Because the pump is delivering a smaller amount than maximum capacity this valve position can be called normal.

If the pump outlet flow is stopped, by the steering movement being blocked for example, the pressure rises in the pipe (1) and the pressure difference on the ends of the control valve is equalized. The spring then pushes the valve back to the left, the connection with the return channel is closed and the pressure rises again.

At maximum pressure (see specification Steering Steering the spring pressure on the safety valve (6), that is the inner part of the control valve, is overcome and oil can pass out to return channels (4), see illustration B. The pressure on the right-hand side of the piston is decreased and the control valve is moved to the right and opens the connection to return channel.

When the pressure has sunk to a normal value the safety valve shuts and the control valve returns to the normal position.