Electric control valves have been more and more widely used in various industrial control systems due to their high control accuracy, convenient installation and commissioning. However, in the process of use, there are also some problems that plague field instrument personnel, that is, the problem of valve leakage. Here we will discuss the common causes and solutions of internal leakage of electric control valves, hoping to help the on-site maintenance personnel of the factory.
1. The zero setting of the actuator is not accurate, and the full closing position of the valve is not reached.
Adjustment method: 1) Manually close the valve (must confirm that it has been completely closed); 2) Then close the valve manually, and the valve will not be screwed with a little force; 3) Twist back (valve opening direction) half a turn; 4) Then adjust the limit.
2. The valve is a downward push closing type, the thrust of the actuator is not large enough, and it is easy to reach the full closing position when there is no pressure, and when there is a downward thrust, it cannot overcome the upward thrust of the liquid, so it is not closed in place.
Solution: Replace the actuator with high thrust, or use the balanced spool to reduce the unbalanced force of the medium.
3. Internal leakage caused by the manufacturing quality of electric control valves
In the production process, the valve manufacturer does not strictly control the valve material, processing technology, assembly process, etc., resulting in unqualified sealing surface grinding, pitting, trachoma and other defective products are not completely eliminated, resulting in internal leakage of electric control valves.
Solution: Rework the sealing face.
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 ambient temperature, pressure and humidity, resulting in the valve positioning inaccuracy, spring fatigue, uneven thermal expansion coefficient and other objective factors, resulting in the internal leakage of the electric control valve.
Workaround: Readjust the limit.
5. Internal leakage caused by the debugging problem of the electric control valve
Affected by the processing and assembly technology, the electric control valve generally has the phenomenon that the electric control valve cannot be opened after the manual closing is tight, such as the stroke of the electric control valve is adjusted smaller through the action position of the upper and lower limit switches, then the electric control valve is not closed tightly or the valve can not be opened in an unsatisfactory state; If the stroke of the electric control valve is adjusted larger, it will cause the over-torque switch protection action; If the action value of the torque switch is adjusted larger, there will be an accident that the deceleration transmission mechanism will be damaged, or the valve will be damaged, or even the motor will be burned. In order to solve this problem, usually, the electric control valve is manually shaken to the end during the commissioning of the electric control valve, and then shake it in the direction of opening, and then the lower limit switch position of the electric door is fixed, and then the electric control valve is opened to the full open position to set the upper limit switch position, so that the electric control valve will not appear to be open after the manual closing is not opened, so that the electric door can be opened and closed freely, but the electric door leakage is caused invisibly. Even if the adjustment of the electric control valve is ideal, because the action position of the limit switch is relatively fixed, the medium controlled by the valve will continue to wash and wear the valve during operation, which will also cause the internal leakage phenomenon caused by the valve is not closed strictly.
Workaround: Readjust the limit.
6. The cavitation corrosion of the valve caused by the wrong selection causes the internal leakage of the electric control valve
Cavitation is related to the pressure difference, when the actual pressure difference of the valve △P is greater than the critical pressure difference △Pc of cavitation, cavitation will occur, and a huge amount of energy will be released when the bubble bursts during the cavitation process, which will have a huge destructive effect on the valve seat, valve core and other throttling elements, and the general valve will run for more than three months or even less under cavitation conditions, that is, the valve suffers from serious cavitation corrosion, resulting in the leakage of the valve seat can reach more than 30% of the rated flow, which is irreparable, therefore, Different types of electric doors have different specific technical requirements, and it is very important to choose a reasonable electric control valve according to the system process.
Solution: Carry out process improvement, choose multi-stage pressure reduction or sleeve control valve.
7. Internal leakage caused by the erosion of the medium and the aging of the electric control valve
After a certain period of operation after the adjustment of the electric control valve, due to the cavitation of the valve and the erosion of the medium, the wear of the valve core and the valve seat, the aging of internal components, etc., the electric control valve will have a large stroke and the electric control valve is not closed tightly, resulting in a large leakage of the electric control valve, and the leakage of the electric control valve will become more and more serious over time.
Solution: Readjust the actuator and perform regular maintenance and calibration.
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