Basic knowledge of valve electric device and parameter setting

Valves electric device is to achieve program-controlled valves, automatic control and remote control indispensable drive equipment, the movement process by stroke, torque or axial thrust to control the size. As the valve actuator operating characteristics and utilization depends on the type of valve, the device specifications and the valve position on the pipeline or equipment. Electric device generally consists of the following components: Special motor, characterized by strong overload? Starting torque? Moment of inertia, short-term intermittent work. Reducing mechanism to reduce the motor output speed. Travel control agencies, to regulate and accurately control the valve opening and closing position. A torque limiting mechanism adjusts the torque (or thrust) so that it does not exceed a predetermined value. Manual? Electric switching mechanism, manual or electric operation of the interlocking mechanism. Opening indicator, used to show the valve opening and closing process in the position. First, according to the type of valve to choose electric actuator 1. Angular travel electric actuator (angle <360 degrees) for butterfly valves, ball valves, plug valves and so on. Electric actuator output shaft rotation less than a week, that is less than 360 degrees, usually 90 degrees to achieve the valve opening and closing process control. Such electric actuator according to the different ways to install the interface is divided into direct-connected, base crank type two. a) Direct connection: refers to the electric actuator output shaft and stem mounted in direct connection. b) base crank type: refers to the output shaft through the crank and stem connected to the form. 2. Multi-turn electric actuators (corner> 360 degrees) for gate valves, globe valves and so on. Electric actuator output shaft rotation is greater than a week, that is greater than 360 degrees, generally need to be lapped in order to achieve the valve opening and closing process control. 3. Straight stroke (linear motion) for single-seat control valve, two-seat control valve. Electric actuator output shaft movement of linear motion, not the rotation form. Second, according to the production process control requirements to determine the electric actuator control mode 1. Switch (open-loop control) switch-type electric actuators generally open or close the valve control, the valve is either in the fully open position, or in the fully-closed position, such valves do not need precise control of the medium flow. Particularly worth mentioning is the switch-type electric actuator due to the different forms of structure can be divided into split structure and integrated structure. Selection must be made on this description, or often occur in the scene of the installation and control system conflicts do not match the phenomenon. a) Split structure (usually called ordinary type): the control unit is separated from the electric actuator. The electric actuator can not control the valve independently, and an external control unit is required to realize the control. Generally, the control unit or control cabinet is used for external control Supporting. The disadvantage of this structure is that it is inconvenient to install the whole system, increase the wiring and installation costs, and prone to failure, not easy to diagnose and repair when the fault occurs, the price is not satisfactory. b) All-in-one structure (often referred to as integral type): The control unit is packaged with the electric actuator and can be operated in real-time without the need of a control unit. The remote control unit can output the relevant control information and operate it remotely. The advantage of this structure is to facilitate the overall system installation, reduce wiring and installation costs, easy to diagnose and troubleshooting. However, the traditional integrated structure of the product there are many imperfections, resulting in a smart electric actuator. 2. Regulated (closed-loop control) Regulated electric actuator not only has the function of a switch-type integrated structure, but also precise control of the valve to regulate the flow of media. a) Control signal type (current, voltage) The control signal of actuator is generally with current signal (4 ~ 20mA, 0 ~ 10mA) or voltage signal (0 ~ 5V, 1 ~ 5V) Signal type and parameters. b) Type of operation (electric open type, electric close type) The operating mode of the regulated electric actuator is generally electric open type (taking 4-20mA control as an example, electric open type means the 4mA signal corresponds to the valve closed and 20mA corresponds Is the valve open), and the other for the electric-type (4-20mA control, for example, electric open type 4mA signal corresponds to the valve open, 20mA corresponds to the valve). Wear-resistant electrode c) loss of signal protection Loss of signal protection refers to the failure of the control signal due to line failures, the electric actuator will control the valve opening and closing to set the protection value, the common protection value is fully open, all off, keep In situ three cases. Third, according to the use of the environment and explosion-proof electrical equipment classified according to the use of the environment and explosion-proof grade requirements, the valve electric device can be divided into ordinary type, outdoor type, flameproof, outdoor flameproof and so on. According to the required torque of the valve to determine the output torque of the electric actuator The torque required to open and close the valve determines the choice of how much the output torque of the electric actuator is generally proposed by the user or the valve manufacturer to choose as the actuator manufacturer only The torque output of the actuator is responsible for the normal opening and closing of the valve required torque by the valve size, pressure and other factors, but the valve manufacturers processing accuracy, assembly process are different, so different manufacturers produce the same specifications of the valve torque There are some differences, even with the same valve manufacturers produce the same specifications of the valve torque is also different, when the type of actuator torque selection is too small will not be able to normally open and close the valve, so the electric actuator must choose a reasonable torque range . Fourth, the correct choice of valve electric device based on: Operating torque: Operating torque is the most important parameter to choose the valve electric device, electric device output torque should be the valve operating torque of 1.2 to 1.5 times. Operation thrust: There are two kinds of main structure of the valve electric device: one is do not configure the thrust plate, the direct output torque; the other is configured thrust plate, the output torque through the thrust plate of the stem nut is converted to output thrust.