The most common types of pneumatic valves are pneumatic control valves, pneumatic ball valves, and pneumatic butterfly valves. This article will analyze in detail the reasons why pneumatic valves cannot be fully closed.
All valves have a certain leakage rate. It is necessary to check whether the leakage rate of the valve exceeds the standard value. If it does, it is a quality issue.
Is the valve stuck by debris? Is the valve stem stuck? Is there a problem with the positioner?
Is the pressure difference before and after the pneumatic control valve too large? Is there a problem with the selection? Is the output force of the actuator too small?
We can first find the cause from the above descriptions and then apply the solutions.
Several solutions for pneumatic valves that cannot be fully closed
If your pneumatic valve has a manual function, you can manually close it each time or have the instrument personnel recalibrate the zero point and positioner.
The closing stroke is not in place, the valve stem is severely worn, and the pressure of the compressed air does not meet the standard. There are many reasons. First, adjust the valve positioner, and then adjust the closing stroke.
Is the valve a pneumatic open or pneumatic close valve? If it is a pneumatic close valve, check whether the air supply pressure and the zero and range adjustment of the positioner are normal. Also, check if the valve core is stuck.
If it is a pneumatic open valve, disconnect the air supply. The valve should be fully closed. If it cannot be fully closed, it may be that there is debris stuck in the valve body.
If the valve cannot be fully closed randomly, it is recommended to check whether the instrument air pressure is sufficient, that is, whether the air pressure output by the positioner can reach the pressure required for the valve to be fully closed. Check whether the air supply pressure is sufficient and whether the valve is stuck or has internal leakage. It is best to adjust the positioner first and try.
Air-to-open valve:
1. The preload force of the spring is insufficient and can be appropriately increased.
2. When the working conditions permit, the valve should be disassembled for a pressure test to check the sealing condition of the valve core and valve seat, as well as whether there is any damage to the valve core and valve seat.
3. If the valve cannot be fully closed again, the valve can be isolated and checked for any foreign objects at the valve core and valve seat.
4. Check if the zero point of the valve is too high.
Air-to-close valve:
1. The preload force of the spring is too large and can be appropriately reduced.
2. When the working conditions permit, the valve should be disassembled for a pressure test to check the sealing condition of the valve core and valve seat, as well as whether there is any damage to the valve core and valve seat.
3. If the valve cannot be fully closed again, the valve can be isolated and checked for any foreign objects at the valve core and valve seat.
4. Check if the air supply pressure of the valve is normal.
5. Check if the diaphragm is damaged.
6. Check if the zero point of the valve is too high. If the valve still cannot be fully closed after the above operations, it is recommended to verify the relevant parameters of the valve to see if there is any discrepancy between the designed parameters and the actual working conditions.