The pneumatic valve actuator is malfunctioning; it is necessary to ensure that the valve remains at a certain opening degree. How to handle this?
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There is a fault with the pneumatic valve actuator; it is necessary to ensure that the valve remains at a certain opening degree. I remember that in the past a handwheel was used to force the valve open, but I can’t recall exactly what it was called.
Does the valve come with a handwheel? If you are using it, first determine the opening degree you need to maintain, such as 10%, then use the handwheel to adjust the valve to that 10% setting; that’s all. The automatic adjustment range of the valve is from 10% to 100%.
If there is a handwheel, use it to adjust the control valve to the desired opening degree； If there is no handwheel, a pneumatic setpoint device can be connected to the diaphragm of the control valve to keep it at the desired opening degree.
A common method used for on-site maintenance is to use instrument air to push the valve to the desired position, and then support the area around the valve stem’s coupling nut with wooden blocks or steel components.
If the positioner fails, it is still necessary to maintain the valve position as it was before the failure; generally, a hold-down valve is installed in the pneumatic circuit to keep the valve position unchanged
The idea mentioned on the 5th floor makes some sense; if nothing is attached to the valve, a pressure reducing valve can be used to connect directly to the membrane head. It is not recommended to perform maintenance or adjustments on the control valve while it is in motion, as this can lead to problems.