Issues related to flow rate calculation for control valves
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During the flow calculation using a control valve, it was found that there is a significant difference in flow rate when the valve stem moves upward and downward (at the same opening degree); I’m not sure what the reason for this is Furthermore, there is very little information available regarding the control valve purchased, and it is not even known what flow characteristics this valve has. I hope experts can offer guidance; thank you!
At the same opening degree, differences in the pressure difference before and after will cause changes in flow rate. F=K√△P
The selection information for control valves includes details on whether a proportional or linear response is required, as well as whether there is any change in pressure before and after the valve is opened or closed
First point: By \"upward\" and \"downward\" that you mentioned, I understand it to refer to the opening and closing of the valve. But, the opening degree you mentioned is the same. Is it the same height measured at the valve stem on-site, or is it the same height displayed in the DCS via feedback from the positioner? This is very crucial. If only the DCS height is consistent while the actual measured height is not, then it is a problem with the locator. Generally, standard valves have specified tolerance requirements for backlash (that is, the upward movement followed by downward movement mentioned by the original poster). There won’t be such a large difference in traffic. If so, it’s just a coincidence that this hysteresis occurs at a sensitive point in the flow rate change. In response to the original poster’s question about traffic characteristics. If the specification requirements at the time of purchase cannot be found. Then it can only be determined through the relationship between changes in opening degree and flow rate. To make a judgment.
I’m not sure what you use for calculations; I use conval here, and it works fine in most cases