Nov.07.2024
Pneumatic valves are widely used in various industrial equipment. The valve is opened and closed by compressed air. The pneumatic actuator can perform fast linear cycles and control the valve switch. It has a simple design and is easy to maintain. It can be used in various harsh working environments, such as explosion safety requirements, and dusty and damp working conditions. It is mainly used in oil, gas, chemical industry, power, printing, painting, mining, pharmaceuticals, and other places.
Air valves are generally divided into normally open and normally closed based on their operating principle.
Air opening and closing are selected taking into account the safety of the process plant. When the air source is shut off, is it safe for the valve to be in the closed or open position?
Air-open type (normally closed type): when the air pressure on the diaphragm head increases, the valve acts in the direction of increasing the opening, and when the upper limit of the input air pressure is reached, the valve is in the fully open state. Conversely, when the air pressure decreases, the valve moves in the direction of closing, and when there is no input air, the valve is fully closed. Usually, we call the air-open type regulating valve the fault closure type valve.
Air-closed type (normally open type) operates in exactly the opposite direction to the air-open type. When the air pressure increases, the valve to close the direction of action; air pressure decreases or no air pressure, the valve to open the direction or full open until. Usually we call the air-off type regulating valve for the failure to open type valve.
During use, several failure points usually occur FO, FC, FL. Fail close/open valve failure refers to the operation of the valve if the gas source fails, i.e. the gas supply is interrupted.
1. When the air valve is shut off, the position of the valve must meet the following conditions:
FC—The air source is lost and the valve is in the closed position.
FO——The air source is lost and the valve is in the open position.
FL——The air source is lost and the valve is in its current position and remains open.
FLC——The air source is lost, the valve maintains its position but tends to close, and the valve is in the closed position (the gas in the cylinder has been exhausted).
FLO——Air source is lost, the valve maintains its position but tends to open, the valve is in the open position (gas in the cylinder has been exhausted)
2. If a control valve or switching valve is involved in the shutoff action of the device, the valve position shall be as follows:
FC——The air source has been lost or the solenoid valve has lost power and is in the closed position.
FO——Air source has been lost or the solenoid valve has lost power and the valve is in the open position.
AFL/EFC——⑴The solenoid valve does not lose power even if the air source is lost, and the valve maintains its position. ⑵Even if the solenoid valve loses power due to the air source being removed, the valve remains in the closed position.
AFL/EFO——⑴Even if the air source disappears, the solenoid valve does not lose power and maintains its position. ⑵Whether the air source is gone or not, the solenoid valve loses power and the valve is in the open position.
Pneumatic valves achieve disconnection, connection, adjustment, and other valve functions through output signals. Its opening and closing speed is relatively fast. Pneumatic valves are often used for two-position high-speed disconnects and can also be used for flow control.
