What to do if the AOX electric control valve is not tightly closed? Several schemes for regulating valve internal leakage
During the use of valves, there are often some troublesome problems, such as whether the valve is tightly closed or not. What should be done? The following are several methods for dealing with internal leakage in control valves.
1. The zero position setting of the actuator is not accurate and has not reached the fully closed position of the valve
1) Manually close the valve (it must be confirmed that it has been fully closed);
2) Apply more force to manually close the valve, whichever cannot be turned slightly with force;
3) Turn back (in the direction of opening the valve) another half turn;
4) Then adjust the limit
2. The valve is a downward push closed type, and the thrust of the actuator is not large enough. When debugging without pressure, it is easy to reach the fully closed position. However, when there is a downward thrust, it cannot overcome the upward thrust of the liquid, so it cannot be closed in place.
Solution: Replace the high thrust actuator or switch to a balanced valve core to reduce the imbalance force of the medium.
3. The internal leakage caused by the manufacturing quality of electric control valves is caused by the valve manufacturer's lax control over valve material, processing technology, assembly process, etc. during the production process, resulting in unqualified grinding of sealing surfaces, incomplete removal of products with defects such as pits and sand holes, resulting in internal leakage of electric control valves.
Solution: Rework the sealing surface.
4. The control part of the electric control valve affects the internal leakage of the valve. The traditional control mode of the electric control valve is through the mechanical control mode such as the valve limit switch and the over torque switch. Because these control elements are affected by the environmental temperature, pressure and humidity, the valve positioning is inaccurate, spring fatigue, uneven coefficient of thermal expansion and other objective factors cause the internal leakage of the electric control valve.
Solution: Readjust the limit.
5. The internal leakage caused by the debugging problem of the electric control valve is generally affected by the processing and assembly process, and there is a phenomenon that the electric control valve cannot be opened after being manually closed tightly. If the stroke of the electric control valve is adjusted smaller by the action position of the upper and lower limit switches, an ideal state of the electric control valve not being tightly closed or the valve not being opened will occur; Adjusting the stroke of the electric control valve larger will cause the over torque switch protection action; If the action value of the torque switch is adjusted larger, there may be accidents such as damaging the deceleration transmission mechanism or valve, or even burning the motor. To solve this problem, usually during the debugging of the electric control valve, manually swing the electric control valve to the bottom, then rotate it one circle in the open direction to set the lower limit switch position of the electric door, and then open the electric control valve to the fully open position and set the upper limit switch position. This way, the electric control valve will not be unable to open after manual closing, which can make the electric door open and close freely, but invisibly cause internal leakage of the electric door. Even if the adjustment of the electric control valve is relatively ideal, due to the relatively fixed action position of the limit switch, the constant erosion and wear of the valve controlled medium during operation can also cause internal leakage caused by the valve not being tightly closed.
Solution: Readjust the limit.
6. The selection error causes cavitation corrosion of the valve, which leads to internal leakage of the electric control valve. Cavitation is related to pressure difference. When the actual pressure difference △ P of the valve is greater than the critical pressure difference △ Pc that generates cavitation, cavitation occurs. During the cavitation process, when the bubble ruptures, it releases huge energy, which has a huge destructive effect on throttle components such as the valve seat and core. Generally, valves operate for three months or even shorter under cavitation conditions, The valve has suffered severe cavitation corrosion, resulting in seat leakage of over 30% of the rated flow rate, which cannot be compensated. Therefore, electric valves for different purposes have different specific technical requirements, and it is crucial to choose electric control valves reasonably according to the system process flow.
Solution: Make process improvements and choose multi-stage pressure reducing or sleeve regulating valves.
7. Due to the erosion of the medium and internal leakage caused by the aging of the electric control valve, after the electric control valve is adjusted and operated for a certain period of time, due to reasons such as cavitation and erosion of the medium, wear of the valve core and valve seat, and aging of internal components, the electric control valve stroke may be too large and the electric control valve may not be tightly closed, resulting in a larger amount of leakage of the electric control valve. Over time, The phenomenon of internal leakage in electric control valves will become increasingly serious.
Solution: Readjust the actuator and perform regular maintenance and calibration.