Is it a problem with the valve, or an issue with the signal from the equipment?
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For the pneumatic control valve, the instrument technician sent a fake signal of 4-20mA, and the valve operated normally. However, when the signal from the plant equipment indicates an opening degree of less than 20%, the valve does not move; once the opening degree increases by more than 20%, the valve suddenly moves to the specified opening degree. Excuse me, what is this problem?
Most valves come equipped with front and rear hand valves as well as bypass lines; it is recommended to disconnect them and take them apart for inspection.
First, check whether there is any sticking in the valve stem and valve core, then check the pneumatic components.
1. Try replacing the safety barrier (you can try removing one from a valve that is not used frequently nearby)； 2. If the safety barrier is ruled out, check the locator and examine whether there is any water ingress in the wiring box; if no signs of water intrusion are present, replace it with a new one if possible. If this has not happened before, valve abnormalities are usually caused by these two situations.
The valve suddenly moves to the specified opening; check the other components in the control circuit
First determine the signal type of your control valve, and then address the issue with the air supply pressure?
Check whether the given current signal from the controller to the valve is correct Another possibility is that there is something stuck inside the valve
Try operating it manually first to see if the valve switches smoothly; if manual operation works fine, it’s likely a problem with the instrument regulator
There is no problem when adjusting the means.
It’s probably because the valve is a bit stuck, or there’s an issue with the initial pressure