What causes fluctuations in Fisher valve positioners?
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Both the valve and the actuator are from Fisher. When the value goes from 0 to 100, there is sticking and noise caused by friction of the valve stem, but no fluctuations occur. However, when the value drops from 100 to 75 or 25, fluctuations occur at those two valve positions, along with noise due to valve stem friction. Can someone explain this? How should it be repaired?
If that’s the case, then it’s likely a problem with the mechanical parts; it’s possible that something has gotten stuck inside the valve core, or that the valve stem has bent during operation
There might be medium on the valve stem; it just needs to be cleaned.