Replacing small-diameter control valves with large-diameter ones
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In our workshop, there is a control valve with a small diameter and low flow rate on the ethylene oxide aqueous solution pipeline. Due to lack of maintenance over time, it has been replaced with an unused control valve of larger diameter. The CV values of these two control valves differ by a factor of 3; as a result, automatic regulation cannot be achieved when using linear characteristics, and the flow rate fluctuates too much, requiring manual adjustment. I would like to ask the experts here: if we switch to equal percentage control and limit the valve position to 50% or 60%, can the flow rate at these positions still meet the maximum flow rate achievable by the original control valve? Is this approach feasible??? If not, please let me know the reasons, preferably along with some relevant information. I’m sorry, but I’m a beginner in instrumentation work... :)
It is best to provide your process parameters to the valve manufacturer so that they can calculate the opening degree for you. At present, the CV value indicates a three-fold difference in opening degrees; larger-diameter valves have much smaller opening degrees compared to smaller valves. However, when the valve opening degree is small, it is difficult to adjust the flow characteristics, and linearity becomes apparent only when the opening degree is larger
It’s best to have specific parameters; re-calculation is necessary. Contact the manufacturer of the unused valves – they will help you out. Without their calculation software, it’s very difficult to resolve the issue on one’s own.
The traffic characteristics will change after the modification; therefore, recalculation is required