The pneumatic control valve cannot be adjusted
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Due to mechanical maintenance of the valve body, the instrumentation staff removed the wires, after which the mechanical valve was taken apart for maintenance. After the maintenance was completed and the instrumentation staff reconnected the wires, it became impossible to make adjustments; the air supply was found to be in good condition. Set it to fully open for 4AM, and set it to fully closed (air shut-off valve) for 5AM or later. It still cannot be adjusted even after setting it according to the instructions (I tried adjusting it multiple times, but I’m not sure if it was done successfully). The same problem persisted even after replacing the valve positioner with a new one. Is it possible that the significant changes that occurred after the valve stem was repaired are the reason for the large discrepancy in the position of the feedback rod after it was connected, compared to its position before disconnection, which in turn makes control impossible? The instrument just had its wires disconnected; nothing else was touched. The valve model is ZPZD3100.
Based on the phenomenon described by the poster, I believe it is due to the incorrect connection position of the feedback rod, which causes a change in the measurement range; adjusting the position of the feedback rod again should resolve this issue.
Photos of the feedback rod should be uploaded, and it should also be stated in the instructions that after reinstallation, the stroke needs to be recalibrated; the feedback rod must be horizontal at half of the stroke length.
In my humble opinion, it can be checked in this way: first, determine whether it is a gas-on valve or a gas-off valve. For a gas-on valve, it closes completely when the air supply is cut off, and it opens fully when air directly reaches the diaphragm head; check then whether the stroke has reached its full extent. For a gas-off valve, the process is reversed. This allows one to determine whether the problem lies with the valve or the actuator. Only by methodically troubleshooting can problems be solved effectively.
Check whether the valve stroke is correct. See if it matches the original itinerary. If the travel distance is short, the valve stem length needs to be shortened.
Thank you all for your answers above; the issue has been resolved – it was caused by too large a change in the position of the feedback rod. :handshake
It might be due to feedback; it’s either fully on or fully off – is the operation of the valve in between linear?
It seems like the itinerary location has changed