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What to do if the electric control valve is not tightly closed? Several schemes for internal leakage of control valves

2023-03-31

During the use of valves, there are often some troubling problems, such as whether the valve is tightly closed or not. What should I do? The following describes several treatment methods for internal leakage of control valves.

1. The zero position setting of the actuator is not accurate and does not reach the full closing position of the valve

Adjustment method:

1) Manually close the valve (it must be confirmed that it has been completely closed);

2) Manually close the valve with additional force, subject to slight force failure;

3) Tighten it back (in the valve opening direction) by half a turn;

4) Then adjust the limit

2. The valve is of the downward push closing type, and the thrust of the actuator is not large enough. When debugging without pressure, it is easy to reach the fully closed position. 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 actuator with a large thrust, or change to a balanced valve core to reduce the unbalanced force of the medium.

3. Due to internal leakage caused by the manufacturing quality of electric control valves, the valve manufacturer did not strictly control the 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 method of the electric control valve is through mechanical control methods such as valve limit switches and over torque switches. Due to the influence of these control elements by ambient temperature, pressure, and humidity, objective factors such as valve positioning misalignment, spring fatigue, and uneven thermal expansion coefficient can cause internal leakage of the electric control valve.

Solution: Readjust the limit.

5. Due to internal leakage caused by debugging problems of electric control valves, due to the influence of processing and assembly processes, it is common for electric control valves to fail to open after being manually closed tightly. If the stroke of the electric control valve is adjusted to be smaller by the action position of the upper and lower limit switches, an undesirable state may occur where the electric control valve is not tightly closed or the valve cannot be opened; Adjusting the stroke of the electric control valve a bit larger will cause the over torque switch protection action; If the action value of the over torque switch is adjusted larger, there may be accidents such as crashing the decelerating transmission mechanism, crashing the valve, or even burning the motor. In order to solve this problem, usually, when debugging the electric control valve, manually swing the electric control valve to the bottom, and then rotate it in the open direction for one circle to set the lower limit switch position of the electric valve. Then, open the electric control valve to the full open position and set the upper limit switch position, so that the electric control valve will not fail to open after being manually closed tightly, so that the electric valve can be opened and closed freely, but it can potentially cause internal leakage of the electric valve. 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 scouring and wear of the valve controlled medium during operation can also cause internal leakage caused by the valve being not tightly closed.

Solution: Readjust the limit.

6. "Incorrect type selection results in cavitation corrosion of the valve, resulting in internal leakage of the electric control valve. Cavitation is related to the pressure difference. When the actual pressure difference △ P of the valve is greater than the critical pressure difference △ Pc that produces cavitation, cavitation occurs. During the cavitation process, when the bubble bursts, it releases enormous energy, causing significant damage to throttle elements such as the valve seat and valve core. Generally, valves operate for three months or even less under cavitation conditions,", That is, the valve suffers from severe cavitation corrosion, resulting in valve seat leakage of up to 30% of the rated flow, which is irreparable. Therefore, electric valves for different purposes have different specific technical requirements, and it is important to reasonably select electric control valves according to the system process flow.

Solution: Carry out process improvement and select multistage pressure reducing or sleeve regulating valves.

7. "Due to media erosion, internal leakage caused by aging of the electric control valve, and after a certain period of operation of the electric control valve after adjustment, due to cavitation and media erosion of the valve, wear of the valve core and valve seat, aging of internal components, and other reasons, the electric control valve stroke may be too large, and the electric control valve may not be tightly closed, resulting in greater leakage of the electric control valve. Over time,", The internal leakage of electric control valves will become increasingly serious.

Solution: Readjust the actuator, and perform regular maintenance and calibration.

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