What to do if a pneumatic control valve doesn’t adjust properly?
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I’m currently conducting IO tests. When adjusting the valves on-site, many of them don’t get adjusted properly – they often fail to open or close fully. I hope experts can share some tips for tuning control valves! !
If the adjustment is not proper, there are several possible reasons. One is that the manufacturer did not set the positioner correctly; in this case, it’s simple – just adjust the positioner. Another reason could be that the manufacturer did not take into account sufficient head pressure in the pipeline when selecting the valve, or the pipeline pressure exceeds the designed value. There’s also the issue of the handwheel: sometimes it isn’t closed or opened fully, and even with DCS control, the valve may not be closed or opened properly
1. Reasons: 1) Severe wear of the valve core and seat; 2) Foreign objects stuck between the valve core and seat; 3) Air leakage in the actuator diaphragm of the control valve; 4) Excessive pre-tensioning force of the zero-point spring; 5) The valve stem is set too short; 6) Large pressure difference before and after the control valve; 7) Fault in the valve positioner
If it is a new product, the reasons are roughly as follows: first, has the valve stroke of the manufacturer been adjusted properly? First, this needs to be determined. Second, the accuracy of the locator is slightly affected due to transportation and handling; a slight adjustment of the locator will suffice. If the product has been in use for some time, it could be a problem with the valve core, leakage in the diaphragm head, or hardware issues such as the valve not being suitable for the pipeline pressure difference.
In some cases, the zero point of the locator has shifted. In some cases, over time foreign particles and wear occur in the valve core and seat, and there may also be a low air supply pressure. The transmission mechanism is stuck.