Questions regarding the nominal diameter of control valves
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Based on the calculations carried out under the process conditions, the nominal diameter of the control valve is larger than the diameter of the pipeline; does this engineering diameter have any practical significance? Has anyone seen this situation before?
It makes no sense; usually the values are less than that, and if they’re greater, it’s likely impossible to keep control.
Perhaps the process conditions were specified incorrectly; I’ve never heard of a control valve having a nominal diameter larger than that of the pipeline.
1) Incorrect input of process conditions. 2) The wrong type of control valve was selected; for example, when the flow rate is high and the pressure difference is low, a GLOBE valve is chosen, and in such cases the calculated diameter might be larger than that of the pipe. In such situations, a butterfly valve should be used instead. If neither of the above two situations applies, it indicates that the process conditions themselves are unreasonable; it is necessary to discuss this with the process engineering team in order to redesign the process requirements.
Agree with the view on floor 4. The process parameters were calculated incorrectly; there is no margin (such as for pressure drop losses) for installing control valves.
It must be a mistake; if the nominal diameter of the control valve is larger than that of the pipeline, how can it be controlled when it is opened to full extent?
This is a principled mistake. There’s no need to question it.
It must be a mistake; this indicates that the mediation range is greater than 100%, which is impossible
Thank you all for the discussion; I now understand! There must be an issue with the process calculation.
It makes sense. It depends on what the situation is. I’ve encountered it; it’s like this. This is a side-line level control loop, and the process operates as a self-pressuring loop with a very small pressure difference; therefore, the valve selected must have a diameter at least equal to that of the pipeline in order to ensure the proper functioning of this control loop. If the valve is chosen to be too small, it will cause throttling, resulting in a high liquid level that cannot drop. There are also self-protecting valves for gases, and it’s possible to choose larger ones as well.
There’s a problem with the process design; otherwise it’s your calculations that are incorrect
If the diameter of the control valve is larger than that of the pipe, it is not possible to ensure controllability throughout the entire range of motion; the control valve will operate at a low opening degree, making it difficult to guarantee control quality.
If the inner diameter of the control valve is larger than the diameter of the pipeline, it will be restricted by the pipeline, and the control valve will not be able to achieve its maximum flow rate; therefore, this is a problem
At this point, the flow rate in the process pipeline is already too high
Since no specific parameters were provided, it is impossible to conduct a calculation; it can only be said that there may be an issue with the selection of the control valve.