Pneumatic valves mainly refer to valves that are activated by cylinders to form a power source through compressed air, thereby achieving the purpose of regulating switches. When the regulating pipeline receives control signals generated from the automation control system, it will adjust relevant parameters (such as temperature, flow rate, pressure, etc.).

Pneumatic valves are mainly composed of three components, namely pneumatic actuator, valve body, and accessories. The actuator includes springs, diaphragms/pistons, pneumatic rods, handwheels, etc. It mainly uses clean compressed air as power, receives 20-100kPa gas signals or 4-20mA electrical signals, and then drives the valve body to move, adjusting the flow area between the valve core and valve seat to achieve the purpose of regulating flow. The valve body is mainly composed of components such as valve disc, valve cage, valve stem, valve seat, and valve cage pressure ring; The attachments mainly include pressure reducing valves, solenoid valves, positioners, current/voltage converters, filters, flow amplifiers, etc. Overall, the working principle of pneumatic valves is as follows: after inputting a pressure signal of 0.02-0.10MPa into the regulator chamber, the thin film will generate thrust, which achieves the purpose of compressing the spring during the downward movement of the thrust plate, thereby pushing the valve stem, push rod, and valve core to continuously move downwards, achieving the purpose of regulating the valve.

Pneumatic valves mainly have the following advantages: firstly, they act quickly and can complete adjustment commands in a short time; secondly, they can cooperate with large cylinders to achieve large torque driving force; thirdly, pneumatic valves can operate safely and stably for a long time in various harsh conditions.

Common faults of pneumatic valves
1. Fault and cause of increased leakage of pneumatic valves
The leakage rate of pneumatic valves mainly depends on the valve switch. In summary, the increase in leakage rate of pneumatic valves is mainly due to the following two factors: firstly, the valve core inside the pneumatic valve wears out due to prolonged use, causing the valve to not close tightly and resulting in an increase in leakage rate; The second is that if there are foreign objects mixed inside the valve or the inner lining is sintered, or under the control of pressure between various media, when the pressure difference of the media is large, it will lead to a decrease in rigidity, causing the valve to not fully close, and ultimately increasing the leakage of the pneumatic valve.

2. Unstable operation faults and causes of pneumatic valves
Both unstable signal pressure and unstable gas source pressure can cause unstable operation of pneumatic valves. Unstable signal pressure can cause unstable output of the regulator, while unstable gas source pressure can cause failure of the pressure reducing valve due to the small capacity of the compressor. It is also possible that the gap between the amplifier spray group baffles in the locator can cause unstable operation of pneumatic valves. In addition, the output pipe or output line is not tight, which can also cause unstable operation of pneumatic valves; The gap formed by friction between the amplifier ball valve and foreign objects can also affect the stability of the pneumatic valve.

3 Pneumatic valve vibration faults and their causes
Pneumatic valves are easily affected by surrounding environmental factors during operation. After a long period of operation, the lining and valve core will form gaps under the action of friction, mechanical equipment with additional vibration around the pneumatic valve, and uneven installation position of the pneumatic valve can cause vibration of the pneumatic valve. In addition, improper selection of the size of the pneumatic valve or when the closing direction of a single seat valve is not consistent with the direction of the medium flow can also cause vibration of the pneumatic valve.

4. Fault and Cause of Slow Action of Pneumatic Valves
The importance of the valve stem is beyond doubt during the movement of pneumatic valves. When the valve stem is bent, it increases the friction generated by its back and forth movement, causing the pneumatic valve to act slowly. When graphite and asbestos packing lubricating oil and PTFE packing are abnormal, it can also cause the pneumatic valve to act slowly. When there is dust inside the valve body or a locator installed inside the pneumatic valve, it will increase the resistance of the pneumatic valve stem to operate, thereby causing the pneumatic valve to act slowly.

5. Pneumatic valve failure and reasons
Air source and signal are the prerequisites and foundation for ensuring the smooth operation of pneumatic valves. If the locator has no air source, the pressure reducing valve may malfunction, and in severe cases, it may even cause filter and pipeline blockage; If the locator has an air source but no output, it will block the throttle hole of the locator; If there is no air source or signal, when the temperature is low and the air source is not turned on, it will fail due to blockage of the pressure reducing valve and air duct, ultimately leading to compressor failure. If there is an air source but no signal, it will damage the regulating mesh and cause air leakage in the corrugated pipe of the locator.