Help needed
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What can cause a control valve or on/off valve to fail to close?
Stuck? No power? Out of air? Is the signal cable broken? The control card is broken; the signal isn’t being sent? Is the actuator broken? Is the locator broken? There are too many; to ask for help, at least describe the specific phenomenon.
Pneumatic or electric? Check whether the filter in front of the pneumatic check valve is clogged, or there is a problem with the air supply, or the diaphragm at the top of the actuator is damaged, resulting in insufficient air pressure and thus preventing it from opening. There may be a fault with the electric actuator or positioner for inspection, and a power outage is also possible. Alternatively, there could be issues such as control system feedback failures, problems with the signal source, or signal lines.
There are too many reasons; it depends on the specific symptoms of the fault, which require a detailed analysis