Why is there a reduction in diameter at the control valve on the pipeline?
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Why is there a reduction in diameter at the control valve on the pipeline?
I have the same problem; in most cases, the control valves shrink in diameter when piping is installed. The exact reason is unknown and needs to be investigated
Selection of valve diameter: It is determined based on the process flow rate, allowable pressure drop, appropriate valve resistance, and most importantly, the optimal control curve of the valve; generally, the nominal diameter of the valve is smaller than that of the process pipeline； Selection of process piping: maximum allowable pressure drop and flow rate ； Thus, since the optimal valve diameter differs from the optimal process pipeline size, how should they be connected? I’m sure it’s due to the diameter change! Using a variable diameter isn’t for any specific purpose; it’s just to connect the two optimal designs together!
The main factor determining diameter reduction is still the process parameters; in other words, if the calculated KV value is too low, in order to improve the accuracy of adjustment and to avoid damage to the valve’s service life due to operation at low opening degrees, diameter reduction is carried out
Your explanation seems reasonable, but it’s a bit far-fetched and doesn’t address the original poster’s question. The control valve is determined based on the maximum operating flow rate and the calculated pressure difference, and its diameter is fixed by verifying the opening degree and the adjustable ratio. Typically, to reduce frictional losses along the pipeline, diameters of 1–2# are commonly chosen; therefore, diameter reductions are often seen at control valves.
The diameter of the control valve is calculated by the instrumentation and control team based on the Cv value, and it is very likely to differ from the pipe diameter. Just knowing this is enough; there’s no need to worry about these details when working on piping.