Why do control valves allow internal leakage? ?
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After looking at the structure of the control valve, it is similar to a globe valve, with the addition of a valve cage; when the control valve is fully closed, the valve stem and the seat are completely sealed. Then why does the control valve still experience internal leakage when it is closed? Please find **. What I’m asking is why there is internal leakage when the control valve is completely closed? Please do not answer off-topic; no, no, it’s not about the leakage level of the control valve
Regarding investments, if one has money, they will choose those with a lower leakage level. The control valve is primarily used for regulating performance; if necessary, front and rear manual valves can also be used to shut it off.
Is the insufficient machining precision causing poor contact between the sealing surfaces? I guess
The pressure at which a control valve shuts off completely is fixed, and the force required to close a globe valve downward is greater than that of a control valve.
Control valves are a general term for a category of valves named according to their function; they are not limited to globe valves only, but also include ball valves, butterfly valves, and those with other designs. The leakage rating you mentioned cannot be ignored; all valves have a leakage rating. For ball valves used for sealing and isolation, a VI rating will definitely result in higher costs compared to a IV rating. The function of a control valve is to regulate the flow of the medium. Unless specifically requested by the user, no manufacturer will voluntarily raise the leakage level beyond the standard requirements, as this would certainly lead to increased costs. We also produce control valve products, including globe valves as well as ball valves. In fact, unless the valve malfunctions or is of poor quality, the leakage that occurs after it fails to close isn’t that severe. If requested by the user, we can also increase the leakage resistance of our valves to achieve a shut-off and sealing function.
In my opinion, there are three reasons for leakage in control valves: First, the control valve operates in a regulating mode for an extended period of time, and the sealing surface is also the throttling surface, which leads to erosion and resulting in poor sealing； Secondly, when the control valve does not require a sealed shut-off, its sealing surface has a low precision level and goes through no processes such as grinding, which leads to leakage. Thirdly, in order to reduce the size of the actuator, the sealing force is not strong enough, which is related to the selection process.
1. Will there be no leaks after pressurizing the new valve once it arrives? 2. The machining precision of the sealing surface of the control valve is crucial; the grinding process is just as important as that for other valves! 3. So just increase the size of the actuator?
Thank you all for your answers, but they all raise doubts. In the sealing tests for international valves, why are control valves not included? In other words, from the very beginning of its design and right from the time it leaves the factory, the control valve is designed to allow internal leakage even when it is fully closed. Why? From a technical perspective, don’t talk about costs! I have never seen a control valve with zero leakage to date