A pneumatic valve is one of the most used devices in various industries in recent years. It is driven by compressed air to realize the opening and closing of the valve. Pneumatic actuators can simply realize fast linear cyclic movement, has simple structure, convenient maintenance, and can be used in various harsh working environments, such as explosion-proof, dusty or humid working conditions. Pneumatic valves are mainly used in petroleum, natural gas, chemical, electricity, printing and dyeing, mining, pharmaceutical and other industries.
Pneumatic valves can be generally divided into valves opened by pressure and valves closed by pressure according to their functions. The choice of opening and closing by pressure is considered from the safety of process production. When the air supply is cut off, whether the regulating valve is safe in the closed position or open position.
Opening by pressure means that when the air pressure on the membrane head increases, the valve moves in the direction of increasing the opening degree. When the upper limit of the input air pressure is reached, the valve is in a fully open state. Conversely, when the air pressure decreases, the valve moves in the closing direction; when no air is input, the valve is fully closed. Therefore, the valve opened by pressure is also called the fail-to-close type (FC).
The moving direction of valves closed by pressure is just opposite to that of valves opened by pressure. When the air pressure increases, the valve moves to the closing direction; when the air pressure decreases or stops, the valve moves to the opening direction or is fully opened. Therefore, it is sometimes called the Fail to Open type (FO).
Then, in the process of use, several fault positions that usually occur are FO, FC and FL. The fault in the valve refers to the action of the valve when the air source fails. For the fault positions of pneumatic valves, they are mainly divided into the following situations:
1. In the case of interlocking action of the pneumatic valve device, the valve position should be in the following situations:
FC: Air supply is lost, and the valve is in a closed position.
FO: Air supply is lost, and the valve is in an open position.
FL: Air supply is lost, the valve is in the time position and has been maintained.
FLC: Air supply is lost; the valve remains in place but tends to close. The valve is in the closed position. The gas in the cylinder is exhausted.
FLO: Air supply is lost, and the valve remains in place but tends to open; the valve is in the open position. The gas in the cylinder is exhausted.
2. When the regulating valve or switching valve participates in the interlocking action of the device, there are the following valve positions:
FC: Air supply loses or the solenoid valve loses power; the valve is in the closed position.
FO: Air supply loses or the solenoid valve loses power; the valve is in the open position.
AFL or EFC: 1. The solenoid valve is not de-energized when the air source is lost, and the valve remains in position. 2. Regardless of whether the air source is lost or not, the solenoid valve is de-energized, and the valve is in the closed position.
AFL or EFO: 1. The solenoid valve is not de-energized when the air source is lost, and the valve remains in position. 2. Regardless of whether the air source is lost or not, the solenoid valve is de-energized, and the valve is in the open position.
The pneumatic valve realizes the functions of cutting off, connecting, and adjusting the valve through the output signal. Its opening and closing speed are relatively fast, which is often used for quick two-position cuting off, and can also be used to adjust the flow. Various control methods can be achieved with different accessories.