The pneumatic butterfly valve closes on its own after being operated manually
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Our unit is equipped with a double-acting pneumatic butterfly valve; when operated manually via the DCS, the valve occasionally closes on its own to 8% when the temperature is low. When the site is switched to manual operation, the DCS cannot be controlled, and it shuts down on its own to 8%. What is the reason for this? If forced to be operated manually on-site, it will also shut down on its own.
It is recommended that, if possible, a valve position verification be conducted to check whether the on-site readings match those of the DCS at each opening degree. Check for leaks in the diaphragms of the valve positioner and the valve actuator’s cylinder, etc.
The details are not very clear. 1. Manual operation at the site – it shuts down on its own; possibly the rack mechanism is damaged. 2. If manual operation at the site works normally, then DCS manual control is used, and it shuts down on its own; there might be condensation in the air supply line. It is recommended that, if possible, the mechanical components be inspected, and the air used for instruments and for driving mechanisms have their contaminants removed
Verification has been done, and the valve openings at the site are basically consistent. Will air leakage due to diaphragm aging cause the valve to close on its own after manual intervention at the site?
Conditionally check the instrument air. What’s unclear now is whether manual intervention was carried out on site; logically, shouldn’t the instrument air be unable to control the valve opening and closing?
Yes. So the rack is suspected. However, the mechanisms installed in different manufacturers may not be identical; therefore, it is still necessary to refer to the diagram of the transmission mechanism.
It’s probably a problem with the valve itself; have the maintenance staff work together with the instrumentation team to fix it