Valve Electric Device is an indispensable driving device to realize valve program control, automatic control and remote control. Its movement process can be controlled by stroke, torque or axial thrust. Because the valve electric device operating characteristics and utilization depends on the type of valve, device specifications and valve in the pipeline or equipment location.
1. Select Electric Actuator According To Valve Type
1.1 Angle Stroke Electric actuator (Angle<360°) is suitable for butterfly valve, ball valve, plug valve, etc. .
Electric actuator output shaft rotation less than a week, that is less than 360°, usually 90° to achieve the valve opening and closing process control. This type of electric actuator according to the installation of different interface is divided into direct-connected type, base crank type two.
A) Direct connection: refers to the electric actuator output shaft directly connected to the valve stem in the form of installation.
B) Base crank type: refers to the output shaft through the crank and stem connection form.
1.2 Multi-turn electric actuators (Angle>360°) for gate valves, globe valves, etc.. Electric actuator output shaft rotation is more than a week, that is more than 360°, generally need to be multi-cycle to achieve the valve opening and closing process control.
1.3 Straight stroke (straight motion) is suitable for single seat regulating valve, double seat regulating valve, etc. . The motion of the output shaft of the electric actuator is linear, not rotational.
2. Determine the control mode of the electric actuator according to the control requirements of the production process
2.1 Switch type (open loop control) switch type electric actuators generally provide open or closed control of the valve, either in fully open position or fully closed position, such valves do not require accurate control of media flow. It is especially worth mentioning that the switch type electric actuator can be divided into two parts and integrated structure because of different structural forms. Type selection must be made to this, or often occur in the field installation and control system conflict and other mismatched phenomena.
A) Split structure (commonly known as common type): The control unit is separated from the electric actuator. The electric actuator can not control the valve by itself, but must be controlled by an additional control unit. The disadvantage of this structure is that it is not convenient to install the whole system, increases the wiring and installation cost, and is easy to appear fault, when the fault occurs, it is not convenient to diagnose and maintain, the performance-price ratio is not ideal.
B) Integrated structure (commonly referred to as Monolithic) : The control unit is integrated with the electric actuator and can be operated in place without the external control unit, and can be operated remotely only by outputting relevant control information. The advantage of this structure is to facilitate the overall system installation, reduce wiring and installation costs, easy diagnosis and troubleshooting. But the traditional integrated structure product also has many imperfect places, therefore has produced the intelligent electric actuator.
2.2 Adjustable (closed-loop control) adjustable electric actuator not only has the function of switch-type integrated structure, but also can accurately control the valve and adjust the medium flow.
A) Control signal type (current, voltage) control signal of regulated electric actuator generally has current signal (4 ~ 20MA, 0 ~ 10MA) or voltage signal (0 ~ 5V, 1 ~ 5V) .
B) Type of work (electric open type, electric close type) regulation type of electric actuator work mode is generally electric open type (4 ~ 20MA control for example, electric open type is 4MA signal corresponding to the valve closed, 20MA corresponding to the valve open) , the other type is electric closed type (4-20MA control for example, electric open type is 4MA signal corresponding to the valve open, 20MA corresponding to the valve closed) .
C) Loss of signal protection means that the electric actuator opens and closes the control valve to the set protection value when the control signal is lost due to the fault of the circuit, etc. .
3. Determine the output torque of the electric actuator according to the torque required to open and close the valve. The torque required to open and close the valve determines how much output torque the electric actuator chooses, which is usually offered 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 the factors such as the size of the valve orifice, working pressure, etc. Therefore, the torque required by the same valve of the same specification varies from one manufacturer to another, even from the same valve manufacturer of the same specification When the choice of actuator Torque is too small will cause the normal opening and closing valve, so electric actuator must choose a reasonable range of torque.
4. According to the use of the environment and explosion-proof grade classification of electric devices according to the use of the environment and explosion-proof grade requirements, electric devices can be divided into general type, outdoor type, flameproof type, outdoor flameproof type and so on.
5. Basis Of Selecting Valve Electric Device Correctly:
5.1 Operating Torque: operating torque is the most important parameter of selecting valve electric device, the output torque of electric device should be 1.2 ~ 1.5 times of the maximum operating Torque of valve.
5.2 Operating Thrust: There are two main types of valve actuator: one is to output torque directly without a thrust plate, and the other is to have a thrust plate with the output torque converted to output thrust by the stem nut in the thrust plate.
5.3 Output Shaft Rotation Number: valve electric device output shaft rotation number of the number of turns with the nominal diameter of the valve, valve stem pitch, number of threads, calculate in terms of m = H / Zs (m is the total number of turns that the electric device should satisfy, h is the valve opening height, s is the stem drive thread pitch, Z is the stem thread head) .
5.4 Stem Diameter: A multi-turn stem valve can not be assembled if the maximum stem diameter allowed by the electric device can not pass through the stem of the supplied valve. Therefore, the electric device hollow output shaft diameter must be greater than the stem stem stem stem diameter stem valve. For some rotary valves and non-return valve stem valves, although do not consider the stem diameter through the problem, but in the selection should also fully consider the stem diameter and keyway size, so that the assembly can work properly.
5.5 Output Speed: Valve opening and closing speed if too fast, easy to produce water hammer phenomenon. Therefore, should be based on different conditions of use, the selection of the appropriate opening and closing speed.
Post time: Jul-28-2021