Electric control valve is composed of control valve and electric device, so when the valve is determined, how to correctly select the electric device is an important factor related to whether the actual use can meet the needs of the project. When selecting the electric device, not only the working environment, electrical control and general technical performance mentioned above should be considered, but also the comprehensive technical performance of the electric device.
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 in use. If the output torque of the selected electric device is too large or insufficient, it is not advisable. Because in general, the electric device manufacturer needs to test and adjust the output torque value when the product leaves the factory, which is relatively accurate. If the output torque margin is too large, the dynamic control valve will have great potential risk. Once the control and protection failure occurs, it will easily cause valve damage (valve stem bending, valve body rupture) phenomenon, which is very easy to cause pipeline system accidents. Therefore, it is not advisable to select too large output torque margin. If the valve cannot be opened in the actual work, it is also unreasonable to choose.
As for the determination of the output speed of the electric device, when the valve has no strict requirements on its opening and closing time, the slower speed should be selected as far as possible.
Because of the unnecessary faster speed, the motor power will be increased under the same torque requirements, which not only wastes energy and increases the project cost, but also makes the electric device volume increase, resulting in waste in many aspects.
At present, there are not many motor specifications (generally 2-3 specifications) designed and equipped in each frame number of the electric device developed and developed in China, and the speed ratio range of the gear pair and worm gear pair in the main drive is limited, so the torque and speed grades of each frame number are not much.
2. Allowable maximum thrust of electric device
If the axial force of the valve is borne by the electric device (i.e. the valve stem nut is in the electric device), its thrust value is not allowed to exceed the allowable value of the electric device.
3. Maximum number of turns of stem nut
When selecting the electric device of multi rotary valve, the maximum number of turns of the stem nut must be stated when the valve is working. In this way, the gear speed ratio of the position indicating mechanism in the electric device can be correctly selected, so that the position indication can have enough precision to meet the observation of the valve opening and closing degree during the valve working process, otherwise, it is easy to cause illusion and affect the normal operation.