Discussion on the failure location (FO, FC, FL) of pneumatic valves

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In valve fault closed/fault open, “fault” refers to the behavior of the valve when there is a problem with the air supply. Regarding the failure positions of pneumatic valves, as I understand it, there are the following situations: 1. When the control valve is not involved in the device’s interlock mechanisms, the valve can be in one of the following states: FC – Loss of air supply; valve in closed position. FO – Loss of air supply; valve in open position. FL – Loss of air supply; valve in its last known position and remains there. FLC – Loss of air supply; valve retains its position but tends to close, eventually ending up in the closed position (when the gas in the cylinder is exhausted). FLO – Loss of air supply; valve retains its position but tends to open, eventually ending up in the open position (when the gas in the cylinder is exhausted). 2. When the control valve or on/off valve is involved in the device’s interlock mechanisms, the valve can be in one of the following states: FC – Loss of air supply or deactivation of the solenoid valve; valve in closed position. FO – Loss of air supply or deactivation of the solenoid valve; valve in open position. AFL/EFC – 1. Loss of air supply but the solenoid valve remains active; valve retains its position ； 2. Whether or not the air supply is lost, if the solenoid valve loses power, the valve remains in the closed position. AFL/EFO – 1: If the air supply is lost but the solenoid valve does not lose power, the valve retains its current position ； 2. Regardless of whether the air supply is lost or the solenoid loses power, the valve remains in the open position