Operating principle of Pneumatic Actuated Ball Valve The most common mechanism for a pneumatic actuator for ball valves is the rack and pinion mechanism. This comprises of the rack (a linear gear) and the pinion (a circular gear). The rack is attached to a piston which is pushed by compressed air to achieve linear motion. This linear motion is converted to circular motion by the pinion. The pinion drives the stem of a ball valve to open and close positions. To control the pneumatic actuator for ball valves, the compressed air is regulated by solenoid valves. Electrical signals from the controller energize the solenoid valve to either open or close positions allowing compressed air to flow through to both piston sides of the pneumatic actuator. The piston pushes the rack which turns the pinion connected to the stem of the ball valve.