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What can I do if I don't choose an electric actuator? Look here!

2022-10-26

1. Select electric actuator according to valve type

There are many types of valves, and their working principles are different. Generally, the opening and closing control is realized by turning the valve plate angle, lifting and lowering the valve plate, etc. When matching with the electric actuator, the electric actuator shall be selected first according to the type of valve.

1.1. Angle travel electric actuator (angle<360 degrees)

The rotation of the output shaft of the electric actuator is less than one circle, that is, less than 360 degrees. Normally, the opening and closing process of the valve is controlled when it is 90 degrees. This kind of electric actuator can be divided into direct connection type and base crank type according to the different installation interface modes.

a) Direct connection type: refers to the type of direct connection between the output shaft of the electric actuator and the valve rod.

b) Base crank type: refers to the form in which the output shaft is connected with the valve rod through the crank. These electric actuators are applicable to butterfly valves, ball valves, plug valves, etc.

1.2. Multi turn electric actuator (angle>360 degrees)

The rotation of the output shaft of the electric actuator is greater than one circle, that is, greater than 360 degrees. It usually takes multiple turns to realize the opening and closing process control of the valve. These electric actuators are applicable to gate valves, globe valves, etc

1.3. Straight stroke (straight movement)

The movement of the output shaft of the electric actuator is linear, not rotational. This kind of electric actuator is applicable to single seat regulating valve, double seat regulating valve, etc.

2. Determine the control mode of the electric actuator according to the production process control requirements

The control modes of electric actuators are generally divided into switch type (open loop control) and regulation type (closed loop control).

2.1. Switch type (open-loop control)

The switch type electric actuator generally realizes the opening or closing control of the valve. The valve is either in the fully open position or in the fully closed position. Such valves do not need to accurately control the medium flow. It is particularly worth mentioning that the switch type electric actuator can also be divided into separate structure and integrated structure due to different structural forms. This must be explained when selecting the model, otherwise it will often conflict with the control system during field installation.

a) Split structure (commonly referred to as ordinary type): the control unit is separated from the electric actuator. The electric actuator cannot control the valve independently, and control can only be achieved by adding a control unit. Generally, the external form is controller or control cabinet. 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. When the failure occurs, it is not convenient for diagnosis and maintenance, and the cost performance is not ideal.

b) Integrated structure (usually referred to as integrated structure): the control unit and electric actuator are packaged as a whole, which can be operated locally without external control unit, and can be operated remotely only by outputting relevant control information. The advantage of this structure is that it is convenient for the overall installation of the system, reduces the 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, which will be explained later.

2.2. Regulating type (closed loop control)

The adjustable 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 flow.

a) Type of control signal (current, voltage)
The control signal of the adjustable electric actuator generally includes current signal (4~20mA, 0~10mA) or voltage signal (0~5V, 1~5V). The type and parameters of the control signal shall be specified when selecting the type.

b) Working mode (electric open type, electric close type)
The working mode of the regulating electric actuator is generally electric open type (taking the control of 4~20mA as an example, the electric open type means that the 4mA signal corresponds to the valve closing, and the 20mA signal corresponds to the valve opening), and the other type is 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 opening, and the 20mA signal corresponds to the valve closing).

c) Loss of signal protection
Loss of signal protection means that when the control signal is lost due to line fault, the electric actuator will open and close the control valve to the set protection value. The common protection values are full open, full close, and remain in place, which are not easy to modify after leaving the factory.

3. Determine the output torque of the electric actuator according to the torque required by the valve

The torque required for the opening and closing of the valve determines the output torque of the electric actuator, which is generally proposed by the user or selected by the valve manufacturer. As an actuator manufacturer, it 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 the valve diameter, working pressure and other factors, but the processing precision and assembly process of the valve manufacturer are different, Therefore, the torque required for valves of the same specification manufactured by different manufacturers is different, even for valves of the same specification manufactured by the same valve manufacturer, the torque of the actuator is too small when selecting the type, which will cause the valve cannot be opened and closed normally. Therefore, a reasonable torque range must be selected for the electric actuator.

4. Determine the electrical parameters according to the selected electric actuator

Because the electrical parameters of different actuator manufacturers are different, it is generally necessary to determine their electrical parameters during design and selection, mainly including motor power, rated current, secondary control circuit voltage, etc. Due to negligence in this respect, the mismatch between the control system and the electric actuator parameters results in open tripping, fuse fusing, thermal overload relay protection tripping and other fault phenomena during operation.

5. Select the enclosure protection grade and explosion-proof grade according to the application occasion

5.1. Enclosure protection grade
The enclosure protection grade refers to the foreign matter prevention and waterproof grade of the electric actuator housing, which is represented by the letter IP followed by two digits. The first digit represents the foreign matter prevention grade from 1 to 6, and the second digit represents the waterproof grade from 1 to 8.

5.2. Explosion proof grade

In places where fire or explosion hazards may occur due to explosive gas, steam, liquid, combustible dust, etc., explosion-proof requirements must be put forward for electric actuators, and explosion-proof forms and categories must be selected according to different application areas. The explosion-proof grade can be indicated by the explosion-proof mark EX and explosion-proof content (refer to Explosion proof Electrical Equipment for Explosive Atmospheres GB3836 － 2000). The explosion-proof signs include: explosion-proof type+equipment category+(gas group)+temperature group.

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