Instrument air failure
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How does the remotely controlled isolation valve operate in the event of a problem with the instrument air?
1. For the remotely operated shut-off valves that have been designed and are now installed for trial use on site, the valve position in the event of a problem with the instrument air is indicated on the P&ID diagram; there are three possible scenarios: the valve opens in the event of an FO failure, it closes in the event of an FC failure, and it remains in its locked position in the event of an FL failure； 2. During the design phase, it is necessary to determine the location where failures in the valves may occur, in order to meet safety and process requirements; this is determined by the process design, with the instrumentation being used to implement it.
Loss of instrument air is just one type of fault. If the valve fails for any reason, it should return to a safe state for the system. This safety state should be determined by the process. If the feed valve of an exothermic reactor fails and remains in the open position, material will continue to flow in, and the reaction will get out of control. This feed valve should clearly be in the fault-off position.
Based on the PID in the design documents, FO, FC, and FL are usually indicated next to the valve icon on the PID.