Rotary Valve

The rotary design control valve uses relative rotational motion of the power steering gear input shaft and control and valve sleeve to direct fluid flow.
^ When the steering wheel is turned, resistance of the wheels and the weight of the vehicle cause a torsion bar to deflect.
^ This deflection changes the position of the input shaft and sleeve ports, directing fluid under pressure to the appropriate end of the power cylinder.
^ The difference in pressure forces on the piston help move the steering gear rack to assist turning effort.
^ The piston is retained directly to the steering gear rack, and the steering gear housing functions as the power cylinder.
^ The fluid in the opposite end of the power cylinder is forced to the control valve and back to the pump reservoir.
^ When the driver stops applying steering effort, the valve is returned back to a centered position by the torsion bar.
^ When this occurs, pressure is equalized on both sides of the piston and the front wheels tend to return to a straight-ahead position.