Electric actuators generally consist of the following parts: Special motor, characterized by strong overload capability, large starting torque, small moment of inertia, short-term and intermittent operation. A speed reduction mechanism for reducing the output speed of the motor. The stroke control mechanism is used to adjust and accurately control the opening and closing position of the valve. A torque limiting mechanism for adjusting the torque (or thrust) and not exceeding a predetermined value. Manual, electric switching mechanism, interlocking mechanism for manual or electric operation. The opening indicator is used to indicate the position of the valve during the opening and closing process. First, select electric actuator according to valve type 1. The angular stroke electric actuator (angle <360 degrees) is suitable for butterfly valves, ball valves, etc. 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 opening and closing process control of the valve. Such electric actuators are divided into direct connection type and base crank type according to different installation interface modes. a) Direct connection: refers to the form in which the output shaft of the electric actuator is directly connected to the valve stem. b) Base crank type: refers to the form in which the output shaft is connected to the valve stem through the crank. 2. Multi-turn electric actuator (angle > 360 degrees) is suitable for gate valves, globe valves, etc. The rotation of the output shaft of the electric actuator is greater than one week, that is, greater than 360 degrees. Generally, multiple turns are required to control the opening and closing process of the valve. 3. Straight stroke (linear motion) is suitable for single seat control valve, double seat control valve and so on. The movement of the output shaft of the electric actuator is linear, not in the form of rotation. Second, determine the control mode of the electric actuator according to the production process control requirements 1. Switch type (open loop control) Switching electric actuators generally control the opening or closing of the valve. The valve is either in the fully open position or in the fully closed position. Such valves do not require precise control of the medium flow. It is particularly worth mentioning that switch-type electric actuators can be divided into split structures and integrated structures due to different structural forms. This must be explained during the selection, otherwise it will often occur in the field installation and conflict with the control system and other mismatches. a) Separate structure (commonly referred to as common type): The control unit is separated from the electric actuator. The electric actuator cannot realize the control of the valve separately. It is necessary to add the control unit to realize the control. Generally, the external controller or control cabinet is used. Matching. The disadvantage of this structure is that it is not convenient for the whole system to be installed, the wiring and installation cost are increased, and the fault is easy to occur. When the fault occurs, it is not convenient for diagnosis and maintenance, and the cost performance is not satisfactory. b) Integrated structure (commonly referred to as integral type): The control unit is integrated with the electric actuator, which can be operated locally without external control unit. The remote control can be operated only by outputting relevant control information. The advantage of this structure is that it facilitates the overall installation of the system, reduces wiring and installation costs, and is easy to diagnose and troubleshoot. However, traditional integrated structural products also have many imperfections, so intelligent electric actuators have been produced. 2. Adjustable type (closed loop control) The regulated electric actuator not only has the function of a switch-type integrated structure, but also precisely controls the valve to regulate the flow of the medium. a) Control signal type (current, voltage) The control type electric actuator control signal generally has a current signal (4~20mA, 0~10mA) or a voltage signal (0~5V, 1~5V). The type and parameter of the control signal should be specified when selecting the type. b) working form (electric open type, electric off type) The working mode of the regulating electric actuator is generally electric opening type (taking 4~20mA control as an example, the electric opening type means that the 4mA signal corresponds to the valve closing, the 20mA corresponds to the valve opening), and the other is the electric switching type. (Taking 4-20 mA control as an example, the electric opening type means that the 4 mA signal corresponds to the valve opening, and the 20 mA 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 faults such as lines, the electric actuator will control the valve to open and close to the set protection value. The common protection values ​​are full open, full off, and in-situ. 3. Electric devices classified according to the 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 and the like. Determine the output torque of the electric actuator based on the torque required by the valve The torque required for the valve to open and close determines the output torque of the electric actuator. It is usually recommended by the user or the valve manufacturer can choose it. As the actuator manufacturer, it is only responsible for the output torque of the actuator. The torque is determined by factors such as valve size and working pressure. However, due to the difference in machining accuracy and assembly process of valve manufacturers, the torque required for different specifications of valves produced by different manufacturers is also different, even if it is produced by the same valve manufacturer. The torque of the specification valve is also different. When the torque selection of the actuator is too small, the valve cannot be normally opened and closed. Therefore, the electric actuator must choose a reasonable torque range. Fourth, the correct choice of valve electric device based on: Operating torque: The operating torque is the main parameter of the valve electric device. The output torque of the electric device should be 1.2 to 1.5 times the large torque of the valve operation. Operational thrust: There are two kinds of main structure of the valve electric device: one is that the thrust plate is not arranged, and the torque is directly output; the other is to configure the thrust plate, and the output torque is converted into the output thrust through the stem nut in the thrust plate. Electric actuator classification and advantages and disadvantages: There are many types of electric actuators. It is called in different industries. It is called valve electric device in the industrial pipe valve industry. It is called electric actuator in the instrument industry, but there is no clear distinction in the industry. The angular stroke, straight stroke and multi-turn actuators are classified according to the way of movement. It is a drive that provides linear or rotational motion, using some kind of drive energy and working under certain control signals, regardless of which classification has its own characteristics. Angle-stroke electric actuators, straight-stroke electric actuators and multi-turn electric actuators Most of the angular stroke and straight stroke actuators are modified on the basis of multi-turn type: based on multi-rotation type, with worm gear worm secondary gearbox to form 0~90° angular stroke electric actuator; A straight-stroke electric actuator is formed by a screw member. Angular stroke: 0~90° angular stroke for controlling angular stroke valves such as ball valves, plug valves, butterfly valves and louver valves; Multi-turn electric actuator Multi-rotation type: It needs to run more than 360° to realize the opening and closing of the valve, mainly used for the shut-off valve, the pipe clamp valve and the diaphragm valve; Straight stroke: the output is the force, the displacement is generated, mainly used for the gate valve and the slide valve. Commonly used for supporting various valves to form electric valves or electric control valves (for example: gate valves, regulating valves, single seat valves, etc.) AC or DC power is used as the driving energy; it is divided into two categories according to the operation mode (electric switch type and electric adjustment type) The utility model has the advantages that the energy is convenient to use, the signal transmission speed is fast, the transmission distance is long, the centralized control is convenient, the sensitivity and the precision are high, the electric adjustment instrument is convenient to cooperate, and the installation wiring is simple. The disadvantage is that the structure is complicated, the average failure rate is higher than that of the pneumatic actuator, and it is suitable for places where the explosion-proof requirements are not high and the gas source is lacking. 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Electric actuator detailed and classification and advantages and disadvantages
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