Thread Content
What do these codes for the failure positions of pneumatic valves mean? FC, FO, FL, FLC, FLO, AFL/EFC, and AFL/EFO refer to the safe position that the valve remains in when there is a failure in the air supply or control system. These are fault states predetermined from a process safety perspective, with different codes corresponding to different fault behaviors. The specific meanings are as follows: 1FC–Fail to Close: When the air supply is lost or the solenoid valve loses power, the valve remains in the closed position; this is also known as fail-closed mode, and it applies to valves that operate on air pressure to stay open. 2FO–Fail to Open: When the air supply is lost or the solenoid valve loses power, the valve remains in the open position; this is known as fail-open mode, and it applies to valves that operate on air pressure to stay closed. 3FL–Fail Lock: When the air supply is lost, the valve maintains its original opening degree before the failure occurred, that is, it retains its fault position. 4FLC: When the air supply is lost, the valve maintains its position but tends to close, eventually ending up in the closed position (when the gas in the cylinder is exhausted). 5FLO: When the air supply is lost, the valve maintains its position but tends to open, eventually ending up in the open position (when the gas in the cylinder is exhausted). When control valves/switch valves are used in device interlock functions, two types of failures—those related to the air supply and those related to the solenoid valve—are considered, resulting in two combined codes: 6AFL/EFC: When the air supply is lost but the solenoid valve does not lose power, the valve remains in its original position; regardless of the status of the air supply, if the solenoid valve loses power, the valve will close. 7AFL/EFO: When the air supply is lost but the solenoid valve remains powered, the valve stays in its original position; regardless of the air supply status, as long as the solenoid valve loses power, the valve will open. The selection of air-open or air-close pneumatic valves for a project is determined based on the safety considerations of the manufacturing process. Whether it is safer for the valve to be in the closed position or the open position when the gas supply is cut off depends on the operating conditions.