How Does a Pneumatic Rotary Valve Actuator Convert Air Pressure into Rotational Motion

Air Pressure Input

Compressed air is directed into one of two chambers (A or B) via a control valve.

In a double-acting actuator, air enters chamber A to push a piston (the "rack") linearly.

In a spring-return actuator, air pushes the piston in one direction, while a spring provides return motion.

Rack-to-Pinion Conversion

The piston's linear motion drives a toothed rack connected to a pinion gear mounted on the valve's shaft.

As the rack moves horizontally, the pinion gear rotates, transmitting torque to the valve stem.

For a 90° quarter-turn valve (e.g., ball or butterfly valve), the pinion rotates the shaft from the fully closed to fully open position (or vice versa).

Reversing Motion

To reverse the valve's position, air is directed to the opposite chamber (B), pushing the rack in the opposite direction.

In spring-return models, air is released from the active chamber, and the spring pushes the piston/rack to reset the pinion.

Air Pressure and Piston Motion

Compressed air acts on a piston within a cylinder, driving it linearly.

The piston is connected to a yoke (a U-shaped frame) that fits over an eccentric plug on the valve shaft.

Eccentric Plug Mechanism

As the piston moves, the yoke follows the eccentric plug's curve, converting linear motion into rotational motion.

This design generates high torque at the start and end of the stroke (ideal for valves requiring heavy initial force), making it suitable for high-pressure applications.