Pneumatic actuator is an actuator that uses pneumatic pressure to drive the opening and closing or regulating of valves, also known as pneumatic actuator or pneumatic device, but commonly referred to as pneumatic head. Pneumatic actuators are sometimes equipped with certain auxiliary devices. Commonly used are valve positioners and handwheel mechanisms. The function of a valve locator is to use 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 directly operate the control valve to maintain normal production when the control system experiences power outage, gas outage, controller output failure, or actuator failure.