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The actuator is extremely important for self-acting control valves; therefore, the selection of an actuator must be done with great care, taking various factors into consideration. When choosing an actuator for a self-acting control valve, the following points should be kept in mind: 1. Consideration of output force – Regardless of the type of actuator, its output force is the force used to overcome the load on the valve (mainly referring to unbalanced forces and torques, as well as friction, sealing forces, gravity, and other related forces). Therefore, for an automatic control valve to function properly, the actuator must be configured to generate sufficient output force to overcome various resistances, thereby ensuring high sealing performance and smooth operation of the valve. For double-acting pneumatic, hydraulic, or electric actuators, a return spring is generally not installed. The magnitude of the force is independent of the direction of operation; therefore, the key to selecting an actuator is to determine the motor’s maximum output force and torque. For single-acting pneumatic actuators, the output force is related to the valve opening, and the force on the valve also affects its motion characteristics; therefore, it is necessary to establish force balance across the entire range of valve openings. 2. Determine the type of actuator for the automatic control valve. After determining the output force of the driving mechanism, select the appropriate one based on the process requirements and operating environment. To meet the on-site explosion protection requirements, pneumatic actuators should be selected, and the junction box must be of explosion-proof type; electric actuators cannot be used. If there are no explosion-proof requirements, pneumatic and electric actuators can be used; however, from an energy-saving perspective, electric actuators should be preferred whenever possible. Although hydraulic actuators are not as widely used as pneumatic or electric actuators, they feature high control precision, fast response speeds, and good stability. Hydraulic actuators are necessary in applications such as the speed control of transparent units in power plants and the temperature control of reactors in catalytic units in oil refineries.