Regarding the calculation of valve diameter, how to take into account the issue of reduced diameter
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Generally, even if the valve diameter corresponding to the calculated Kv value meets the requirements for the degree of opening, if the pipe diameter is too large, it is possible to consider reducing it. There is a saying that it can be reduced by at most half or by two sizes. The question is: why can’t it be reduced more? Insufficient traffic? Is there a theoretical basis to calculate and verify exactly how much reduction is possible, and at what point reduction becomes a problem?
That is, the diameter of the control valve can be calculated based on two main parameters: the flow rate specified by the process engineering team and the corresponding valve pressure drop. Generally, the calculated valve diameter is slightly smaller than the pipe diameter, so a reduction in diameter is necessary. However, too large a reduction in diameter leads to excessive energy loss. If the calculated valve diameter is much smaller than the pipe diameter, there are two possible reasons: either the pipe size was chosen to be too large for the required flow rate, or the pressure drop across the valve might be very high. In either case, it represents an unreasonable design. Of course, there are exceptions; some valves do have a high pressure drop, in which case the diameter may need to be reduced significantly. But from experience, downgrading from second to third gear is not considered small.