Differences in the structure between regulating butterfly valves and switching butterfly valves themselves
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Are regulating butterfly valves and switching butterfly valves the same in terms of their structural design, that is, aspects such as the valve body and valve stem, aside from the valve positioner and solenoid valve?
It’s the same. A control butterfly valve becomes a on/off butterfly valve when the positioner is removed, while a on/off butterfly valve becomes a control butterfly valve when a positioner is added.
I heard that there is still a difference. Today, a butterfly valve manufacturer said that a control valve can be converted into a on/off valve, but an on/off valve cannot be converted into a control valve. In other words, manufacturers that can produce control valves can generally also produce on-off valves, but those that can produce on-off valves may not necessarily be able to produce control valves. But since the switch butterfly valves in their factory are all made by their own company’s control butterfly valves, he isn’t very clear about the differences. But he is sure that there are some differences, probably on the valve plate.
What LZ said about ‘the control valve can be replaced with a gate valve’ also depends on the specific circumstances. Common gate valves include ball valves, butterfly valves, and eccentric valves; in fact, it’s mainly the shape of the valve core that determines which type is suitable. It’s appropriate to use a linear or quick-opening type control valve as a gate valve, but valve cores with a proportional or parabolic shape might not be suitable for this purpose.
Control valves are required to have a equal percentage flow characteristic; at the very least, they should have a linear flow characteristic； The requirement for on-off valves is a fast-opening flow characteristic; at the very least, a linear flow characteristic is acceptable ； All butterfly valves I have seen have a linear flow characteristic, so there is no distinction between those used for regulation and those used for switching; positioners are used to regulate butterfly valves, while they are not needed for switching them.
Control valves have high requirements for sealing – they must not leak and should exhibit low resistance; otherwise, the dead zone and hysteresis will be too large, resulting in poor control performance. It doesn’t matter what type of valve it is; as long as it can be opened and closed, that’s fine.
The most fundamental reason for the existence of manual-automatic valves is to reduce the labor intensity of people, especially for diameters above DN250. We have processed valve stems with long stroke lengths, and installed them in conjunction with pneumatic actuators, electric actuators, and so on; we have also seen control ball valves produced by some small valve manufacturers. As for manual and control butterfly valves, they seem to differ little in terms of the valve disc and valve stem, so it is feasible to perform interchangeable modifications. But it’s hard to say whether the control requirements are met, as there are significant differences in terms of the valve’s flow capacity calculation and the required control precision. These are immature opinions for reference only.