Since the electric valve is composed of a valve and an electric device, 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 an electric device, not only the aforementioned working environment, electrical control and general technical performance should be considered, but also the comprehensive technical performance of the electric device should be comprehensively considered.
1. The output torque and speed of the electric device
The output torque value is one of the important technical parameters of the electric device, and it is also an important parameter that needs to be selected in use. If the output torque of the electric device selected when assembling the electric valve is too large or insufficient, it is not desirable. Because in general, electric device manufacturers need 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 electric valve will have great potential danger. Once the control and protection failure occurs, it will easily cause valve damage (the valve stem is bent, the valve body is broken), and it is very easy to cause damage to the valve. Plumbing system accident. Therefore, it is not advisable to select too large output torque margin. If the valve cannot be opened in actual work, it is also an unreasonable choice.
Regarding the determination of the output speed of the electric device, when the valve does not have strict requirements on its opening and closing time, the slower speed should be selected as much as possible.
Because of the unnecessary high speed, the motor power will be increased under the same torque requirement, which not only wastes energy, increases the project cost, but also increases the volume of the electric device, causing waste in many aspects.
At present, the domestic self-developed electric device has a small number of motor specifications designed and used in each frame size (generally 2-3 specifications), and the range of the speed ratio of the gear pair and the worm gear pair in the main drive is limited. , so there are not many torque bins and speed bins for each frame size.
2. The maximum thrust allowable value of the electric device
If the valve axial force is borne by the electric device (that is, 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. The maximum number of turns of the stem nut
When selecting an electric device for a multi-turn valve, the maximum number of turns of the valve stem nut must be specified, 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 sufficient accuracy to meet the valve operation. During the process, observe the degree of opening and closing of the valve, otherwise it is easy to cause misunderstanding and affect the normal work.
4. Allowable value of stem diameter
When selecting an electric device for a lift stem valve, attention should be paid to the diameter of the valve stem that it allows to pass, and the diameter of the valve stem must be smaller than this value. In addition, for the multi-turn electric device, the requirements for the height of the valve stem cover (related to the valve diameter) should also be put forward when selecting. Rotary stem valves are available without a stem cover.
5. Connection between valve and electric device
The connection type and size of the valve and the electric device should conform to the national standards: GB/T12222-1989 Connection of multi-turn valve drive device, GB/T12223-1989 Connection of part-turn valve drive device.
At present, the electric device of part-turn valve has a mechanical limit to prevent the disc position from being unable to be judged. The corresponding relationship between the connection screw hole and the keyway position between this kind of valve and the electric device is strictly required.