The electric control valve is composed of a combination of a regulating valve and an electric device. Therefore, how to correctly select the electric device after the valve is determined is an important factor related to whether it can meet the engineering needs in actual use. When selecting the electric device, not only the above-mentioned working environment, electrical control and general technical performance should be considered, but also the comprehensive technical performance of the electric device should be fully considered. 
1. Output torque and speed 
of electric device The output torque value is one of the important technical parameters of the electric device, and it is also an important parameter to be selected during use. It is not advisable to use excessive or insufficient output torque of the electric device selected when grouping the regulating valve. Because of the general situation, the electric device manufacturer needs to test and adjust the output torque value when the product is shipped, which is relatively accurate. If the excessive output torque surplus is selected, the movable regulating valve will have great potential danger. Once the control and protection failure occurs, the valve will be easily damaged (the valve stem is bent and the valve body is broken). Caused a pipe system accident. Therefore, it is not advisable to choose an excessive output torque margin. If you can not open the valve in the actual work is also an unreasonable choice. 
Regarding the determination of the output speed of the electric device, when the valve does not have strict requirements for its opening and closing time, it should try to use a slower speed. 
Because of the unnecessary speed, the motor power will be increased under the same torque requirement. This will not only waste energy, increase the construction cost, but also cause the electric device to increase in size and cause many wastes. 
At present, the number of electric motors designed and equipped in each frame is small (usually 2-3 specifications), and the speed ratio range of the gear and worm gears in the main transmission is limited. Therefore, there are not many torque bins and speed bins for each frame number. 
2. Maximum allowable thrust value of the electric device 
If the axial force of the valve is borne by the electric device (ie, the stem nut is in the electric device), its thrust value must not exceed the allowable value of the electric device. 
3, the maximum number of turns of the stem nut
When selecting the multi-turn valve electric device, it is necessary to explain the maximum number of turns of the stem nut when the valve is working, so that the relevant gear ratio of the position indicating mechanism in the electric device can be correctly selected so that the position indication has enough accuracy to meet the valve working process. The observation of the degree of opening and closing of the valve may cause illusions and affect normal work.