Valve electric device is an indispensable device to realize valve programmable control, automatic control and remote control. Its motion process can be controlled by stroke, torque or axial thrust. Because the working characteristics and utilization rate of the electric valve device depend on the type of valve, the working specifications of the device and the position of the valve on the pipeline or equipment. Therefore, the correct choice of valve electric device is very important to prevent overload.
Usually, the correct choice of valve electric device is based on the following:
1 Operating Torque
The operating moment is the most important parameter to select the valve electric device. The output moment of the electric device should be 1.2-1.5 times of the maximum operating moment of the valve.
2 Operational Thrust
The main structure of the valve electric device has two kinds: one is to output the torque directly without the thrust disc; the other is to configure the thrust disc, and the output torque is converted to the output thrust through the valve stem nut in the thrust disc.
3 Number of rotation cycles of output axes
The number of rotating rings 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 threaded heads.
4 Stem diameter
For multi-turn , if the maximum diameter of the stem allowed by the electric device cannot pass through the valve stem of the matched valve, the electric valve such as electric actuated ball valves cannot be assembled. 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 open stem valve. For some rotary valves and CONCEALED-ROD valves in multi-rotary valves, although the passage of stem diameter is not considered, the diameter of stem and the size of the key groove should also be fully considered when selecting and matching, so that the valve can work normally after assembly.
5 Output Speed
If the opening and closing speed of the valve is too fast, it is easy to produce a water hammer phenomenon. Therefore, we should choose the appropriate opening and closing speed according to different conditions of use.
Valve electric devices such as electric actuated butterfly valves have special requirements, that is, they must be able to limit the torque or axial force. Usually, the valve electric device adopts the coupling which restricts the torque. When the specifications of electric devices are determined, the control torque is also determined. Generally, the motor will not be overloaded if it runs in a predetermined time.
In the past, fuses, overcurrent relays, thermal relays and thermostats were used to protect motors, but these methods have their own advantages and disadvantages. There is no absolutely reliable protection method for the variable load equipment of electric devices. Therefore, it is necessary to adopt various combinations, which can be summed up in two ways: one is to judge the increase or decrease of the input current of the motor; the other is to judge the enthusiastic condition of the motor itself. Either way, the time margin given by the thermal capacity of the motor should be taken into account.
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