March 10, 2025
There may be several reasons why a pneumatic control valve does not close in place:
1. Signal problems
Valve control signal transmission problems, may be a signal line failure, or control system in the sensor, transmitter and other equipment failure.
2. Pneumatic control valve itself
Valve internal parts wear, loose, etc. lead to valve closure is not tight. May be the valve seat, valve plate and other parts are damaged or aging.
3. Pneumatic device problems
Pneumatic device in the air control components are damaged, such as air control valves, cylinders, etc., resulting in insufficient power transmission, the valve is not closed in place.
4. Pressure problems
If the import and export pressure imbalance, or the media flow rate is too high, may lead to the valve closure is not complete.
5. Temperature problems
If the medium temperature is too high, it may lead to expansion of the valve material, resulting in the closure is not in place.
The most common pneumatic valves are pneumatic control valves, pneumatic ball valves and pneumatic butterfly valves. This article analyzes in detail what are the reasons for pneumatic valves not closing?
Valves have a certain amount of leakage, to see whether the leakage of the valve exceeds the standard specified value, more than is a quality problem.
Is the valve stuck by debris? Is the valve stem stuck? Why is the positioner malfunctioning?
Is the pressure difference between the front and rear of the pneumatic control valve too large, and there is a problem with the selection? Is the actuator output force too small?
If your pneumatic valve has a manual, then stop it every time and let the manual shake it to death, or let the instrumentation personnel, re-calibrate it, and re-calibrate the zero point and the positioner;
The stroke of the off position is not in place, the valve stem is badly worn, whether the compressed air pressure is up to standard, there are many reasons, the first valve positioner to rectify a little, and then adjust the stroke of the off position;
Valve is a gas open or gas shut-off valve. If it is a gas-off valve, you can look at the air source pressure, the positioner zero range adjustment is normal, and is the spool of the valve with or without the card, and so on.
If the valve is gas open, the gas source will be disconnected, the valve should be closed if it is not closed, it may be the valve body with or without foreign objects stuck in the problem;
If the valve appears randomly shut down phenomenon, it is recommended to check whether the instrument wind pressure is sufficient, that is, whether the output of the positioner wind pressure can reach the pressure under the closed state of the regulating valve; to see whether the gas pressure is sufficient, and then see whether the valve is stuck, or internal leakage, which is also shut down. It is best to adjust the positioner first try;
Air open valve:
1. the spring preload is not enough, you can increase some appropriate
2. working conditions allow, the valve should be removed to do a pressure test, through which you can check the spool valve seat sealing, as well as the spool and the valve seat whether there is damage.
3. if it occurs again, the case of shutdown, you can cut out the valve, check the spool valve seat whether there is a foreign body
4. Check whether the zero point of the valve is high or not
Air off the valve:
1. the spring preload is too large, you can reduce the preload appropriately
2. working conditions allow, the valve should be removed to do a pressure test, through which you can check the spool valve seat sealing, as well as the spool and the valve seat whether there is damage.
3. if it occurs again, can not close the situation, you can cut out the valve, check the spool valve seat whether there is a foreign body
4. check whether the valve's air pressure is normal
5. check whether the diaphragm is broken
6. check whether the zero point of the valve is high if the above work is not closed after the situation, it is recommended to check the relevant parameters of the valve to see whether the design of the relevant parameters and the actual working conditions are different.
In short, the reasons for the pneumatic control valve closed in place may be multifaceted, need to consider a variety of potential problems, careful inspection and maintenance.
