Time：2023-06-07
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1. Select the electric actuator according to the valve type
There are quite a number of types of valves, and the working principle is not the same. Generally, the opening and closing control is achieved by rotating the valve plate Angle, lifting the valve plate, etc. When matching with the electric actuator, the electric actuator should first be selected according to the type of valve.
1.1. Angular travel electric actuator (Angle <360 degrees)
The rotation of the output shaft of the electric actuator is less than one week, that is, less than 360 degrees, usually 90 degrees, to achieve the valve opening and closing process control. This type of electric actuator is divided into two types: direct connection type and base crank type according to the different installation interface methods.
a) Direct connection: refers to the electric actuator output shaft and valve stem directly connected installation form.
b) Base crank type: it refers to the form in which the output shaft is connected to the valve stem through a crank. This kind of electric actuator is suitable for butterfly valve, ball valve, plug valve, etc.
1.2. Multi-turn electric actuator (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 process control of opening and closing the valve. This kind of electric actuator is suitable for gate valve, stop valve, etc.
1.3. Straight stroke
The motion of the output shaft of the electric actuator is linear motion, not rotation. This kind of electric actuator is suitable for single-seat regulating valve, two-seat regulating valve, etc.
2. Determine the control mode of the electric actuator according to the production process control requirements
The control mode of electric actuators is generally divided into two categories: switching type (open loop control) and regulating type (closed loop control).
2.1. Switch type (open loop control)
The switch type electric actuator generally realizes the open or close control of the valve, and the valve is either in the fully open position or in the fully closed position. Such valves do not need to control the medium flow ******. In particular, it is worth mentioning that switching electric actuators can be divided into separate structures and integrated structures due to different structural forms. This must be explained when selecting, otherwise it will often occur in the field installation and control system conflicts and other mismatches.
a) Split structure (commonly known as the common type) : the control unit is separated from the electric actuator, the electric actuator cannot control the valve separately, and the control unit must be added to achieve control. Generally, the external controller or control cabinet form is used for matching. The disadvantage of this structure is that it is not easy to install the system as a whole, increase the wiring and installation costs, and it is easy to fail, when the failure occurs, it is not easy to diagnose and maintain, and the cost performance is not ideal.
b) Integrated structure (usually called integral type) : the control unit and the electric actuator are packaged into one, which can be operated on the spot without an external control unit, and can be operated remotely only by outputting relevant control information. The advantages of this structure are convenient for the overall installation of the system, reduce wiring and installation costs, and easy diagnosis and troubleshooting. However, the traditional integrated structural products also have many imperfections, so the intelligent electric actuator is generated, and the intelligent electric actuator will be explained later.
2.2. Control type (closed loop control)
Regulating electric actuator not only has the function of switching integrated structure, it can also control the valve ******, thus ****** adjust the medium flow.
a) Type of control signal (current, voltage)
The control signal of the regulating electric actuator generally has a current signal (4 ~ 20mA, 0 ~ 10mA) or a voltage signal (0 ~ 5V, 1 ~ 5V), and the type of control signal and parameters should be clearly defined when selecting.
b) Working form (electric on type, electric off 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 refers to the 4mA signal corresponding to the valve close, 20mA corresponds to the valve open), and the other is electric close type (taking the control of 4-20mA as an example, the electric open type refers to the 4mA signal corresponding to the valve open, 20mA corresponds to the valve close).
c) Loss of signal protection
Loss of signal protection means that when the control signal is lost due to a fault such as a line, the electric actuator will control the valve to the set protection value. The common protection value is fully open, fully closed, and in situ, and it is 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 to open and close the valve determines how much output torque the electric actuator chooses, generally put forward by the user or the valve manufacturer itself, as the actuator manufacturer is only responsible for the output torque of the actuator, the torque required for normal opening and closing of the valve is determined by the valve diameter size, working pressure and other factors, but because the valve manufacturer processing accuracy, assembly process is different. Therefore, the torque required by the same specification valve produced by different manufacturers is also different, even the torque of the same specification valve produced by the same valve manufacturer is also different, and the torque selection of the actuator is too small when the selected type will cause the valve to be unable to open and close normally, so the electric actuator must choose a reasonable torque range.
4. Determine the electrical parameters according to the selected electric actuator
Due to the differences in the electrical parameters of different actuator manufacturers, the electrical parameters are generally determined when designing and selecting, mainly motor power, rated current, secondary control loop voltage and so on. Often negligent in this respect, the result is that the control system and the electric actuator parameters do not match, resulting in the working time and space tripping, fuses blown, thermal overload relay protection tripping and other failures.
5, according to the use of the selection of shell protection level, explosion-proof level
5.1. Case protection class
Shell protection grade refers to the shell of the electric actuator's object protection and waterproof grade, which is expressed by the letter IP followed by two digits, ****** digits 1 to 6 indicate the object protection grade, and the second digit 1 to 8 indicate the waterproof grade.
5.2. Explosion-proof class
In places where explosive gas, steam, liquid, flammable dust, etc. may cause fire or explosion danger, it is necessary to put forward explosion-proof requirements for electric actuators, and select explosion-proof forms and categories according to different application areas. Explosion-proof level can be expressed by explosion-proof mark EX and explosion-proof content (refer to "Explosion-proof electrical equipment for Explosive Environments" GB3836-2000). The content of explosion-proof mark includes: explosion-proof type + equipment category + (gas group) + temperature group.