How to select electric actuators

Electric actuators, also known as electric devices, intelligent Electric Actuators, and Electric Actuators, are mainly divided into switching type and adjustment type, with various torques, and are used in various types, various calibers, and various torque valves.

1. Select the control mode of the Electric Actuator according to the on-site production process control requirements 
　　The control modes of electric actuators are generally divided into two categories: switching type (open-loop control) and regulating type (closed-loop control). 
1. Switching type (open-loop control):
On-off electric actuators typically open or close valves that are either fully open or fully closed, and do not require precise control of the flow of the medium. In particular, it is worth mentioning that switching electric actuators can also be divided into split structure and integrated structure due to different structural forms. This must be explained when selecting the model, otherwise it will often occur in the field installation and other mismatch phenomena such as conflicts with the control system. 
a) Split structure (usually called ordinary type): the control unit is separated from the electric actuator, the electric actuator can not realize the control of the valve alone, and the external control unit must be added to achieve the control, and the controller or control cabinet is generally used externally to match. The disadvantage of this structure is that it is not convenient for the overall installation of the system, increases the wiring and installation costs, and is prone to failure, and is not convenient for diagnosis and maintenance when the fault occurs, and the cost performance is not ideal.

b) Integrated structure (usually called integral type): the control unit and the electric actuator are packaged as a whole, and can be operated on the spot without an external control unit, and can be operated remotely by simply outputting relevant control information. The advantages of this structure are that it is convenient for the overall installation of the system, reduces wiring and installation costs, and is easy to diagnose and troubleshoot. However, the traditional integrated structure products also have many imperfections, so the intelligent electric actuator has been produced, and the intelligent electric actuator will be explained later. 2. Regulating type (closed-loop control) Regulating electric actuator not only has the function of switching integrated structure, but also can accurately control the valve, so as to accurately adjust the medium a) Control signal type (current, voltage) The control signal of the regulated electric actuator generally has a current signal (4~20mA, 0~10mA) or a voltage signal (0~5V, 1~5V), and the type and parameters of the control signal need to be clarified when selecting the type.  b) Working form (electric open type, electric off type) The working mode of the regulating electric actuator is generally electric open type (taking 4~20mA control as an example, electric open type means that the 4mA signal corresponds to the valve close, and 20mA corresponds to the valve open), and the other is the electric close type (taking the control of 4-20mA as an example, the electric open type means that the 4mA signal corresponds to the valve open, and 20mA corresponds to the valve off).  c) Loss of signal protection Loss of signal protection refers to the loss of control signals due to faults such as lines, the electric actuator will open and close the Control Valve to the set protection value, the common protection value is fully open, fully closed, keep in place three situations, and it is not easy to modify after leaving the factory.

2. Select the electric actuator according to the type of valve
There are quite a lot of types of valves, and the working principle is not the same, generally to rotate the angle of the valve plate, lift the valve plate, etc. to achieve opening and closing control, when matched with the electric actuator, the electric actuator should be selected according to the type of valve. 
1. Angular turn electric actuator (turning angle The rotation of the output shaft of the electric actuator is less than one week, that is, less than 360 degrees, and usually 90 degrees to realize the opening and closing process control of the valve. This kind of electric actuator is divided into two types: direct connection type and base crank type according to the different installation interface methods. The common ones are Electric Butterfly Valves and electric ball valves.
a) Direct connection: refers to the direct connection installation of the output shaft of the electric actuator and the valve stem.
b) Base crank type: refers to the form in which the output shaft is connected with the valve stem through the crank. These electric actuators are suitable for butterfly valves, ball valves, plug valves, etc.
2. Multi-turn electric actuator (turning angle> 360 degrees) 
The rotation of the output shaft of the electric actuator is greater than one week, that is, greater than 360 degrees, and it generally takes many turns to realize the opening and closing process control of the valve. This kind of electric actuator is suitable for inlet gate valves, inlet globe valves, etc., which constitute electric gate valves and electric globe valves.
3. Linear stroke (linear motion) 
　　The movement of the output shaft of the electric actuator is linear motion, not rotation. These electric actuators are suitable for single-seat Control Valves, double-seat Control Valves, etc.

3. Determine the electrical parameters according to the requirements of the working conditions 
　　Due to the differences in the electrical parameters of different actuator manufacturers, it is generally necessary to determine their electrical parameters when designing and selecting models, mainly including motor power, rated current, secondary control loop voltage, etc. Often negligence in this regard, as a result, the parameters of the control system and the electric actuator do not match, resulting in the operation of the empty open trip, fuse blow, thermal overload relay protection and other fault phenomena. 
4. Determine the output torque of the electric actuator according to the torque required by the valve 
　　The torque required for valve opening and closing determines how much output torque the electric actuator selects, generally proposed by the user or selected by the valve manufacturer, as the actuator manufacturer is only responsible for the output torque of the actuator, the torque required for the normal opening and closing of the valve is determined by factors such as the size of the valve diameter and the working pressure, but because of the difference in the processing accuracy and assembly process of the valve manufacturer, the torque required for the valve of the same specification produced by different manufacturers is also different, even if the torque of the valve of the same specification produced by the same valve manufacturer is also different. If the torque of the actuator is too small, it will not be able to open and close the valve normally, so the electric actuator must choose a reasonable torque range. 
5. Select the shell protection level and explosion-proof level according to the use occasion
1. Enclosure protection level 
The enclosure protection level refers to the anti-foreign object and waterproof level of the shell of the electric actuator, which is represented by adding two digits after the letter IP, the first digit is represented by 1~6 and the second is indicated by 1~8 waterproof level. For example, the imported electric actuator of VTON in the United States has a common protection level of IP65, IP66, IP67, and IP68.
2. explosion-proof grade
　　In places where explosive gases, vapors, liquids, combustible dusts, etc. may cause fire or explosion hazards, it is necessary to put forward explosion-proof requirements for  electric actuators , and select explosion-proof forms and categories according to different application areas. The explosion-proof level can be indicated by the explosion-proof mark EX and the explosion-proof content (refer to "Explosion-proof Electrical Equipment for Explosive Atmospheres" GB3836-2000). The content of the explosion-proof mark includes: explosion-proof type + equipment category + (gas group) + temperature group.