What is a valve electric device?
What is a valve electric device?
Valve electric device is a device that uses electricity to drive opening and closing or regulating valves.
The 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. The working characteristics and utilization of the valve electric device depend on the type of valve, the working specifications of the device and the position of the valve on the pipeline or equipment.
Electric devices generally consist of the following parts:
- Special motor, characterized by strong overload capacity, large starting torque, small moment of inertia, short-time and intermittent work;
- Deceleration mechanism to reduce the output speed of the motor;
- Stroke control mechanism to adjust and accurately control the opening and closing position of the valve;
- Torque limiting mechanism to adjust the torque (or thrust) and make it not exceed a predetermined value;
- Manual and electric switching mechanism, interlocking mechanism for manual or electric operation;
- The opening indicator is used to show the position of the valve during the opening and closing process.
Choose electric actuator according to valve type
Quarter-turn electric actuator
Angular stroke electric actuator (angle of rotation <360 degrees)-suitable for butterfly valves, ball valves, plug valves, etc.
The rotation of the output shaft of the electric actuator is less than one revolution, 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.
Direct connection type: refers to the form in which the output shaft of the electric actuator is directly connected to the valve stem.
Base crank type: refers to the form in which the output shaft is connected to the valve stem through a crank.
Multi-turn electric actuator
Multi-turn electric actuators (angle of rotation> 360 degrees)-suitable for gate valves, globe valves, etc.
The rotation of the output shaft of the electric actuator is more than one circle, that is, more than 360 degrees. Generally, it takes more than one circle to realize the valve opening and closing process control.
Straight stroke (linear motion)-suitable for single-seat control valves, double-seat control valves, etc.
The motion of the output shaft of the electric actuator is linear motion, not rotating.
Determine the control mode of the electric actuator according to the production process control requirements
Control mode of electric actuator
|Switch type (open loop control)||Switch-type electric actuators generally realize the opening or closing control of the valve. The valve is either in the fully open position or in the fully closed position. This type of valve does not require precise control of the medium flow. It is particularly worth mentioning that switch-type electric actuators can be divided into split structure and integrated structure due to different structural forms. This must be explained when selecting the model, otherwise there will often be mismatches such as conflicts with the control system during on-site installation.|
|1. Split structure (usually called ordinary type): The control unit is separated from the electric actuator. The electric actuator cannot control the valve alone. It must be controlled by an external control unit. Generally, the external controller or control cabinet is used for control. Matching. The disadvantage of this structure is that it is inconvenient for the overall installation of the system, increases wiring and installation costs, and is prone to failure. When a failure occurs, it is not easy to diagnose and repair, and the cost performance is not ideal.|
|2. Integrated structure (usually called integral type): The control unit and the electric actuator are packaged as a whole. It can be operated on the spot without external control unit, and can be operated remotely only by outputting relevant control information. The advantage of this structure is to facilitate the overall installation of the system, reduce wiring and installation costs, and facilitate diagnosis and troubleshooting. However, traditional integrated structure products also have many imperfections, so intelligent electric actuators are produced.|
|Regulation type (closed loop control)||Regulating electric actuators not only have the function of an on-off integrated structure, but also can accurately control the valve and adjust the medium flow.|
|1. Type of control signal (current, voltage). Regulating electric actuator control signals generally have current signals (4~20mA, 0~10mA) or voltage signals (0~5V, 1~5V). The type of control signal and parameters should be clarified when selecting the model.|
|2. Working form (electric opening type, electric closing type). Regulating electric actuators generally work as electric open type (take 4-20mA control as an example, electric open type means that 4mA signal corresponds to valve closing, and 20mA corresponds to valve opening), and the other is electric closing type (Take 4-20mA control as an example, the electric opening type means that the 4mA signal corresponds to the valve opening, and the 20mA signal corresponds to the valve closing).|
|3. Loss of signal protection. Loss of signal protection means that when the control signal is lost due to line faults, the electric actuator will open and close the control valve to the set protection value. The common protection values are fully open, fully closed, and keep in place.|
Electric devices classified according to use environment and explosion-proof grade
- According to the use environment and explosion-proof grade requirements, the electric device of the valve can be divided into ordinary type, outdoor type, explosion-proof type, outdoor explosion-proof type, etc.
- 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 the output torque of the electric actuator. It is generally proposed by the user or selected by the valve manufacturer. As the actuator manufacturer, it is only responsible for the output torque of the actuator. The valve is required for normal opening and closing. The torque of the valve is determined by the valve diameter, working pressure and other factors. However, due to the difference in the processing accuracy and assembly technology of the valve manufacturer, the required torque of the valve of the same specification produced by different manufacturers is also different, even if it is produced by the same valves manufacturers. The torque of the specifications of the valve is also different. When the torque of the actuator is selected too small, it will cause the valve to be unable to open and close normally, so the electric actuator must select a reasonable torque range.
The basis for correct selection of valve drive device
The operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric device should be 1.2~1.5 times the maximum valve operating torque.
There are two main structures of the valve electric device: one is not equipped with a thrust plate and directly outputs torque; the other is equipped with a thrust plate, and the output torque is converted into output thrust through the stem nut in the thrust plate.
Number of turns of output shaft
The number of turns of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the stem, and the number of thread heads. It should be calculated as M=H/ZS (M is the total number of turns that the electric device should meet, and H is the valve Opening height, S is the thread pitch of the stem drive thread, Z is the number of stem threads).
For multi-turn rising stem valves, if the maximum stem diameter allowed by the electric device cannot pass through the stem of the matched valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the rising stem valve. For part-turn valves and dark-stem valves in multi-turn valves, although the passage of the stem diameter does not need to be considered, the stem diameter and the size of the keyway should also be fully considered when selecting, so that it can work normally after assembly.
If the opening and closing speed of the valve is too fast, water hammer is likely to occur. Therefore, the appropriate opening and closing speed should be selected according to different use conditions.
Source: China Electric Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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