A pneumatic actuator is an actuator that uses air pressure to drive the opening and closing or adjusting the valve. It is also called a pneumatic actuator or a pneumatic device, but it is generally called a pneumatic head. Pneumatic actuators are sometimes equipped with certain auxiliary devices. Commonly used are valve positioner and handwheel mechanism. The role of the valve positioner is to use the feedback principle to improve the performance of the actuator, so that the actuator can achieve accurate positioning according to the control signal of the controller. The function of the handwheel mechanism is to use it to directly manipulate the control valve to maintain the normal production when the control system has no output due to power failure, gas failure, or the controller has no output or the actuator fails.