Pneumatic actuator is an actuator that uses pneumatic pressure to drive the opening and closing or regulating valve. It is also called pneumatic actuator or pneumatic device, but it is generally called pneumatic head. Pneumatic actuators are sometimes equipped with certain auxiliary devices. Commonly used are valve positioner and handwheel mechanism. The function of the valve positioner is to improve the performance of the actuator by using the feedback principle, so that the actuator can realize accurate positioning according to the control signal of the controller. The function of hand wheel mechanism is to directly operate the control valve to maintain the normal production when the control system is powered off, gas stops, the controller has no output or the actuator fails.