The power steering oil pump generates the oil pressure and the oil enters into the rotary valve. And the torsion bar is twisted by the force between the steering wheel rotation and the resistance of the tire to the ground. At a high speed of vehicle, the oil passing the rotary valve comes into the solenoid valve through the lower hole and goes out through the upper hole flowing the connecting space of piston. At this time the piston is pushed back away due to the spring force overcoming the solenoid plunger. The oil flows through the space between the piston and side wall. And then the oil flows again into the rotary valve and finally is drained into the reservoir through the drain hole between the rotary valve and the torsion bar. Therefore,the oil pump pressure does not affect the steering effort.

As the vehicle speed decreases, the hole of piston connecting the left chamber and right chamber is gradually closed while the oil pressure produced by oil pump is being transferred to the left chamber. Therefore, the steeringeffort is reduced.

The operation procedure of right turn is the reverse of left turn.