Causes and solutions of internal leakage of pneumatic control valve

Pneumatic control valve is more and more widely used in various industrial control systems because of its high control precision, easy installation and debugging. However, in the process of using, there are also some problems that are bothering the field instrument personnel, namely, the leakage of valve. Here we discuss the common causes and solutions of the leakage of pneumatic regulating valve, hoping to help the maintenance personnel in the factory.

1. The zero position of the actuator is not set accurately and the valve is not fully closed. Adjustment method: 1) manually close the valve (it must be confirmed that it has been completely closed); 2) Close the valve manually again with a little force, which shall prevail; 3) Screw back (open valve direction) for half a turn; 4) then adjust the limit.

2. The valve is push down and closed. The thrust of the actuator is not large enough. It is easy to reach the full close position when there is no pressure. When there is lower thrust, the liquid upward thrust cannot be overcome, so it can not be closed in place. Solution: replace the actuator with high thrust or the balanced valve core to reduce the unbalanced force of medium.

3. Internal leakage caused by the manufacturing quality of pneumatic regulating valve

The valve manufacturer has not strict control over the valve material, processing process and assembly process during the production process, which causes the sealing surface to be grinded unqualified, and the defects such as pitting point and sand hole are not completely eliminated, which causes the leakage of the pneumatic control valve. Solution: reprocess sealing surface.

4. The control part of pneumatic regulating valve affects the internal leakage of the valve

The traditional control mode of pneumatic regulating valve is through mechanical control mode such as valve limit switch and over torque switch. Due to the influence of ambient temperature, pressure and humidity, these control elements cause valve positioning misalignment, spring fatigue, uneven coefficient of thermal expansion, etc., which causes the internal leakage of pneumatic regulating valve. Solution: readjust the limit.

5. Internal leakage caused by the commissioning of pneumatic regulating valve

Due to the influence of processing and assembly process, pneumatic regulating valve is generally closed manually and cannot be opened. If the stroke of pneumatic regulating valve is adjusted slightly by the action position of upper and lower limit switch, the valve is not closed tightly or the valve cannot be opened; If the stroke of the pneumatic regulating valve is adjusted larger, the over torque switch protection action will be caused; If the action value of over torque switch is adjusted larger, the accident of crashing down the transmission mechanism or valve or even burning the motor will occur. To solve this problem, in general, when the pneumatic regulating valve is debugged, manually shake the pneumatic control valve to the bottom, then swing it one turn in the open direction, set the lower limit switch position of the pneumatic valve, and then open the pneumatic regulating valve to the full open position and the upper limit switch position. Thus, the pneumatic control valve will not open manually and then the pneumatic valve can not be opened, so that the pneumatic valve can be opened and closed freely, But invisible causes the leakage of the pneumatic door. Even if the adjustment of pneumatic regulating valve is ideal, because the action position of limit switch is relatively fixed, the medium controlled by the valve will wash and wear the valve constantly during operation, which will cause the leakage caused by the valve not closing tightly. Solution: readjust the limit.

6. The cavitation corrosion of valve caused by wrong selection causes the leakage of pneumatic regulating valve

Cavitation is related to pressure difference. When the actual pressure difference of valve is greater than the critical pressure difference △ PC, cavitation will occur. During cavitation, the bubble will release huge energy, which will cause great damage to throttle elements such as valve seat and valve core. Generally, the valve can run for three months or even shorter under cavitation condition, that is, the valve suffers from serious cavitation corrosion, The leakage of valve seat can reach more than 30% of rated flow, which can not be compensated. Therefore, different uses of pneumatic valve have different specific technical requirements. It is very important to select the pneumatic regulating valve reasonably according to the system process. Solution: to improve the process, select multi-stage pressure reducing or sleeve regulating valve.

7. Internal leakage caused by medium scour and aging of pneumatic regulating valve

After the adjustment of the pneumatic regulating valve, it has been operated for a certain time. Due to the cavitation of the valve, the erosion of medium, the wear of valve core and valve seat, and aging of internal components, the phenomenon of large stroke and tight closing of pneumatic regulating valve will occur, which will cause the leakage of pneumatic regulating valve to become larger. With the passage of time, the leakage in the pneumatic control valve will become more and more serious. Solution: readjust the actuator and maintain and correct it regularly.