According to different classification methods, the actuators of control valves are classified differently.

(1) Classification by energy used

According to the energy used, actuators are divided into pneumatic, electric, hydraulic and manual types.

Pneumatic actuators have the characteristics of long history, low price, simple structure, stable performance, convenient maintenance and intrinsic safety, so they are widely used. According to the different components, pneumatic actuators can be divided into diaphragm type, roller diaphragm type, bellows type, cylinder piston type, gear rack type, fork type and vane type. The small diaphragm actuator is a pneumatic actuator with a multi-spring structure launched in recent years.

Electric actuators have the characteristics of being able to directly connect electric instruments or computers and do not require electrical conversion links, but they are expensive and complex in structure. When used, explosion-proof and other issues need to be considered. According to the working principle and application occasions, electric actuators can be divided into linear, angular, multi-turn and electromagnetic actuators.

Hydraulic actuators have the advantage of large thrust (or thrust torque), but the device is large in size and the flow path is complex. It is often used in applications requiring large thrust (torque). Electro-hydraulic actuators convert electrical signals into hydraulic signals to drive the actuator. Gas-hydraulic actuators convert air pressure signals into hydraulic signals to drive the actuator. Hydraulic actuators directly receive hydraulic signals and drive the actuator.

Manual actuators are often used when the actuator fails or is in the process of starting and stopping. The operator changes the flow area in the valve body through the manual actuator to change the fluid flow. It is usually used in conjunction with other actuators.

(2) Classification by the direction of movement of the actuator output

According to the direction of movement of the actuator output, the actuator is divided into positive-acting and negative-acting actuators. Positive-acting actuators are actuators whose output rods extend outward as the input signal increases and can automatically retract inward as the input signal decreases. Reverse-acting actuators are actuators whose output rods retract inward as the input signal increases and can automatically extend outward as the input signal decreases.

(3) Classification by the type of actuator output displacement

According to the type of actuator output displacement, the actuator is divided into linear actuators, angular actuators and multi-turn actuators. Linear actuators output linear displacement. Angular-turn actuators output angular displacements that are less than 360°. For example, an actuator for a butterfly valve with a rotation angle of 90° or 60°. Multi-turn actuators are similar to angular-turn actuators, but the angular displacement can be multiple turns.

(4) Classification by actuator action mode

According to the actuator action mode, actuators are divided into two categories: continuous and discrete. The output of a continuous actuator is a continuously changing displacement signal. The output of a discrete actuator is a switching displacement signal. Solenoid valves are commonly used electric discrete control valves, and safety vent valves are also common discrete control valves.

(5) Classification by actuator installation method

According to the actuator installation method, actuators are divided into direct-mounted and side-mounted actuators. Direct-mounted actuators are directly installed on the regulating mechanism. Side-mounted actuators are installed on the side of the regulating mechanism. They change the displacement direction and force through a force-enhancing device.

(6) Classification by the type of actuator input signal

According to the type of actuator input signal, actuators are divided into analog actuators and digital actuators. Analog actuators receive analog signals, such as 20~100kPa air pressure signals, 4~20mA standard current signals, etc. Digital actuators receive digital signals, usually a series of binary signals, which are used to open and close the corresponding digital valves or adjust the opening of the control valve after digital-to-analog conversion. With the application of fieldbus technology, actuators that receive fieldbus digital signals are being widely used.

(7) Classification by the action characteristics of actuator output and input

According to the action characteristics of actuator output and input, actuators are divided into proportional type, proportional-integral type and other types. Proportional type The output of the actuator is linearly related to the input signal. The output of the proportional-integral actuator is the sum of the proportional and integral effects of the input signal.