The actuator is an essential part of the automatic control system. Its function is to accept the control signal sent by the controller and change the size of the controlled medium, so as to maintain the controlled variable at the required value or within a certain range. According to its energy form, actuators can be divided into three categories: pneumatic, hydraulic and electric. Pneumatic actuators use compressed air as energy source. They are characterized by simple structure, reliable action, stable operation, large output thrust, convenient maintenance, fire and explosion prevention, and low price. Therefore, they are widely used in chemical, paper, and oil refining production processes. It can be conveniently used in conjunction with passive instruments. Even when using electric instruments or computer control, as long as the electric signal is converted into a standard pressure signal of 20-100kPa by an electric-pneumatic converter or an electric-pneumatic valve positioner, pneumatic actuators can still be used. The electric actuator has convenient energy access and rapid signal transmission, but its structure is complex and its explosion-proof performance is poor. The hydraulic actuator is basically not used in the chemical, oil refining and other production processes. It is characterized by a large output thrust.