The control valve opens fully automatically in the absence of a signal
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Experts, I’m facing an issue with a control valve; I would appreciate your advice. After a fault causing automatic full opening occurs in the pneumatic control valve, once the signal line is disconnected and air is supplied, it will still open fully automatically even in the absence of a signal. Replacing the pilot valve didn’t help either; the coil resistance is normal. Please, those who have encountered similar problems, help me out.
The actuators for such valves vary, as do their signal settings. Specifically, the guidance for controlling the opening and closing of this valve should start by checking from the valve’s air supply side. It’s best to send a video showing whether there is leakage in the piston or diaphragm, or issues with the solenoid valve…… There are many possible problems, but checking each part individually is quite simple; this is for reference only.
Does the control valve operate in FC mode or FO mode? What is the position of the control valve when the air supply is disconnected?
It was confirmed to be a problem with the positioner, but even after replacing it with a new pilot valve and torque motor, the issue persisted; the only solution was to replace the entire positioner.
The control valve will automatically open fully when there is air supply despite a power outage; it’s possible that your control valve is of the air-operated shut type, meaning the spring inside the diaphragm is located beneath the diaphragm, and in the event of a fault the spring will push the diaphragm upward, causing the valve to remain in the fully open position
Yours is of the normally closed type, right? Normally closed means it closes when there is no air flow and opens when air flow is present; the opposite is true for normally open types