How to choose the right electric control valve actuator devices
The electric valve actuator device is an indispensable device for realizing the valve control electrically, automatic control and remote control. The movement process can be controlled by the stroke, torque or axial thrust. Since the operating characteristics and utilization rate of the modulating valve actuator device depend on the type of control valve, the working specification of the device, and the position of the control valve on the pipeline or equipment, the correct selection of the control valve electric device prevents overloading (work transfer) The moment is higher than the control torque).
In general, the correct choice for adjusting the valve's electric device is as follows:
Operating torque: The operating torque is the most important parameter for selecting the electric device of the regulating valve. The output torque of the electric device should be 1.2 to 1.5 times the maximum torque for adjusting the valve operation.
Operational thrust: There are two types of mainframe structures for adjusting the valve electric device: one is to configure the thrust plate without directing the thrust plate; 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.
The number of rotations of the output shaft: the number of rotations of the output shaft of the regulating valve is related to the nominal diameter of the regulating valve, the pitch of the valve stem, and the number of threads. It should be calculated according to M=H/ZS (M is the electric device should meet) The total number of revolutions, H is the adjustment valve opening height, S is the stem drive thread pitch, Z is the stem thread number).
Stem Diameter: For multi-turn type bright rod control valve, if the maximum stem diameter allowed by the electric device cannot pass the valve stem of the control valve, it cannot be assembled into an electric control valve. Therefore, the inner diameter of the hollow output shaft of the electric unit must be larger than the outer diameter of the stem of the rod adjustment valve. For the partial rotary adjustment valve and the dark rod adjustment valve in the multi-turn control valve, although the problem of the diameter of the stem is not considered, the diameter of the stem and the size of the keyway should be fully considered in the selection, so that the assembly can work normally. .
Output speed: If the opening and closing speed of the valve is adjusted too fast, water hammer is likely to occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
Regulating the valve actuator electric device has its special requirements that it must be able to limit the torque or axial force. Usually the electric valve device is adjusted to use a torque limiting coupling. When the specifications of the electric device are determined, the control torque is also determined. Generally running in a predetermined time, the motor will not be overloaded. However, if the following conditions occur, the overload may be caused: first, the power supply voltage is low, the required torque is not obtained, and the motor stops rotating; second, the torque limiting mechanism is set incorrectly to be greater than the stopped torque. Cause continuous excessive torque generation, so that the motor stops rotating; Third, intermittent use, the generated heat accumulation exceeds the allowable temperature rise value of the motor; Fourth, for some reason, the torque limiting mechanism circuit fails, causing the torque to pass Large; five is the use of ambient temperature is too high, relatively reducing the thermal capacity of the motor.
In the past, the protection of the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods have their own advantages and disadvantages. For the variable load device of the electric device, there is no absolute and reliable protection method. Therefore, various combinations must be adopted, which can be summarized in two ways: one is to judge the increase and decrease of the input current of the motor; the other is to judge the heat of the motor itself. In either case, the time margin given by the thermal capacity of the motor must be considered.
Generally, the basic protection method of overload is: using a thermostat for overload protection of continuous or jog operation of the motor; using a thermal relay for the protection of the motor stall; and using a fuse or an overcurrent relay for a short circuit accident.
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