In this instance we are referring to rotary 90 degree switch Pneumatic Actuators (You can even get linear in addition) which are built to change a valve (usually ball, butterfly or plug) through ninety degree rotation (open and close). Pneumatic air pressure is utilised to work the actuator. The bottom https://butterfly-valve94702.blogripley.com/17443560/not-known-facts-about-pneumatic-actuator-solenoid-valve