The Fault State of Control Valves
This article is mainly about finding out the fault state of the control valve and ensuring the safety of the device fault.
Here we only discuss the fault location of the pneumatic diaphragm regulating valve and single-acting pneumatic shut-off valve. When selecting a control valve, it is reasonable to determine the fault location from the perspective of "fault safety" to protect the safety of equipment and personnel. According to the technological requirements, when a fault occurs, it is one of the effective measures to ensure the safety of the device in case of fault.
Little knowledge of valves:
Gas loss-safety: when the driving energy is lost, the valve shut-off element will be fully opened, fully closed, or left in the last position, and any position is to protect the technological process to a safe state; Loss of gas-closing: when the driving energy is lost, the valve shutoff element tends to close; Loss of gas-opening: when the driving energy is lost, the valve shutoff element tends to open position; Fault position: after the valve loses the driving power, specify the position of the valve, that is, the action of the valve when the instrument air (the air source is lost) or the power supply of the solenoid valve fails (applicable to the solenoid valve with power on, but not applicable to the solenoid valve with power off).
The valve fault location is analyzed in three cases as follows:
Situation 1
There are the following three situations in the position where the regulating valve loses air supply, air supply pressure < working pressure or power supply (no 24V power supply, output current < 4mA or > 20mA): FC (Failed Close)—the air source is lost and the valve is in the closed position. FO (Failed Open, i.e., fail open, valve closed)—the air source is lost and the valve is in the open position; FL (Failed Lock)—failure retention, and the valve keeps the position before failure.
Situation 2
In the case of adjusting the gas tank (according to the capacity of the gas tank and the gas consumption in the gas tank), the valve position should have the following two situations: FLC—The gas source is lost, the valve is in position but tends to close, and the valve is finally in the closed position (the gas in the cylinder is exhausted); FLO—The air source is lost, the valve remains in position but tends to open, and the valve is finally in the open position (the gas in the cylinder is exhausted).
Situation 3
Control valves or on-off valves (equipped with solenoid valve) position has the following situations:
FC—Loss of air supply or solenoid valve, and the valve is in the closed position.
The fo—The air source is lost or the solenoid valve is out of power, and the valve is in the open position.
AFL—Air source is lost (the solenoid valve is not powered off), and the valve is in position.
EFC—The solenoid valve is out of power and the valve is in the closed position.
EFO—The solenoid valve loses power and the valve is in the open position.
Here we only discuss the fault location of the pneumatic diaphragm regulating valve and single-acting pneumatic shut-off valve. When selecting a control valve, it is reasonable to determine the fault location from the perspective of "fault safety" to protect the safety of equipment and personnel. According to the technological requirements, when a fault occurs, it is one of the effective measures to ensure the safety of the device in case of fault.
Little knowledge of valves:
Gas loss-safety: when the driving energy is lost, the valve shut-off element will be fully opened, fully closed, or left in the last position, and any position is to protect the technological process to a safe state; Loss of gas-closing: when the driving energy is lost, the valve shutoff element tends to close; Loss of gas-opening: when the driving energy is lost, the valve shutoff element tends to open position; Fault position: after the valve loses the driving power, specify the position of the valve, that is, the action of the valve when the instrument air (the air source is lost) or the power supply of the solenoid valve fails (applicable to the solenoid valve with power on, but not applicable to the solenoid valve with power off).
The valve fault location is analyzed in three cases as follows:
Situation 1
There are the following three situations in the position where the regulating valve loses air supply, air supply pressure < working pressure or power supply (no 24V power supply, output current < 4mA or > 20mA): FC (Failed Close)—the air source is lost and the valve is in the closed position. FO (Failed Open, i.e., fail open, valve closed)—the air source is lost and the valve is in the open position; FL (Failed Lock)—failure retention, and the valve keeps the position before failure.
Situation 2
In the case of adjusting the gas tank (according to the capacity of the gas tank and the gas consumption in the gas tank), the valve position should have the following two situations: FLC—The gas source is lost, the valve is in position but tends to close, and the valve is finally in the closed position (the gas in the cylinder is exhausted); FLO—The air source is lost, the valve remains in position but tends to open, and the valve is finally in the open position (the gas in the cylinder is exhausted).
Situation 3
Control valves or on-off valves (equipped with solenoid valve) position has the following situations:
FC—Loss of air supply or solenoid valve, and the valve is in the closed position.
The fo—The air source is lost or the solenoid valve is out of power, and the valve is in the open position.
AFL—Air source is lost (the solenoid valve is not powered off), and the valve is in position.
EFC—The solenoid valve is out of power and the valve is in the closed position.
EFO—The solenoid valve loses power and the valve is in the open position.
