Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question dated 2020-09-07
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Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-09-07: Discussion question: 228. How can one determine if the diaphragm of a control valve is damaged?
The liquid level measurement indicates a high level, and the regulator’s output is also high; however, the control valve still cannot open
The liquid level measurement indicates a high level, and the regulator’s output is also high; however, the control valve still cannot open
The method for judging the answer given upstairs can only indicate that there is a problem at the site, but it cannot determine whether it is a damaged diaphragm (failure to operate of the valve, low air supply pressure, or a faulty actuator could all be the cause). To determine whether the diaphragm is damaged or not, it’s necessary to check on-site whether there is any leakage from the vent hole of the valve actuator.
Use your hand to check whether air is leaking from the diaphragm of the control valve; if air is present, it indicates that the diaphragm of the control valve is damaged.
If the control valve does not reach the desired position even when a normal signal is applied, and if the output pressure indicated by the valve positioner of the on-site control valve is normal but there is air leakage from the exhaust hole of the on-site valve actuator, it indicates that the diaphragm of the control valve is damaged.
When the control valve diaphragm head is kept under air supply (with pressure below 3 kilograms), if air continues to leak from the exhaust port of the diaphragm head, it indicates that the diaphragm is damaged.
If the control valve does not reach the desired position even when a normal signal is applied, and if the output pressure indicated by the valve positioner of the on-site control valve is normal but there is air leakage from the exhaust hole of the on-site valve actuator, it indicates that the diaphragm of the control valve is damaged.
If the control valve does not reach the desired position even when a normal signal is applied, and if the output pressure indicated by the valve positioner of the on-site control valve is normal but there is air leakage from the exhaust hole of the on-site valve actuator, it indicates that the diaphragm of the control valve is damaged.
If the control valve does not reach the desired position even when a normal signal is applied, and if the output pressure indicated by the valve positioner of the on-site control valve is normal but there is air leakage from the exhaust hole of the on-site valve actuator, it indicates that the diaphragm of the control valve is damaged.
The liquid level measurement indicates a high level, and the regulator’s output is also high; however, the control valve still cannot open