Analysis of Methods for Addressing Internal Leakage in Electric Control Valves
Electric control valves are specialized valves designed to regulate the flow of a medium. These valves automatically control the valve opening based on measured parameters (such as temperature, pressure, or flow rate) to maintain a constant measured parameter. Due to the precise regulation capabilities of electric control valves, internal leakage has become a significant weakness of such products.
The following sections describe several methods for addressing internal leakage in control valves.
1. The zero-position setting of the actuator is inaccurate, and the valve has not reached the fully closed position.
Adjustment method:
Manually close the valve completely (must confirm it is fully closed)
Then manually close the valve with force, until it cannot be turned further with slight force
Then turn it back (in the valve opening direction) by half a turn
Then adjust the limit switch
2. The valve is a downward-pushing closure type. The actuator's thrust is insufficient. During testing without pressure, it is easy to achieve the fully closed position. However, when downward thrust is applied, it cannot overcome the upward thrust of the liquid, resulting in incomplete closure.
3. Internal leakage caused by manufacturing quality issues in electric control valves. Valve manufacturers fail to strictly control material quality, processing techniques, and assembly processes during production, resulting in unqualified sealing surface grinding and the retention of defective products with pits or sand holes, leading to internal leakage in electric control valves.
4. Internal leakage of electric control valves caused by control components. Traditional control methods for electric control valves rely on mechanical components such as valve limit switches and over-torque switches. However, these control elements are influenced by environmental factors such as temperature, pressure, and humidity, leading to issues like valve positioning inaccuracies, spring fatigue, and uneven thermal expansion coefficients, which contribute to internal leakage in electric control valves.
Solution: Re-adjust the limit switches.
5. Internal leakage caused by issues during the commissioning of electric control valves. Due to manufacturing and assembly processes, electric control valves commonly exhibit the phenomenon where the valve cannot be opened electrically after being manually closed tightly. If the travel of the electric control valve is adjusted to be smaller by setting the action positions of the upper and lower limit switches, it may result in the valve not closing tightly or failing to open fully; if the travel is adjusted to be larger, it may trigger the over-torque switch protection mechanism. If the action value of the over-torque switch is set too high, it may cause damage to the reducer transmission mechanism or the valve, or even burn out the motor. To address this issue, during electric control valve commissioning, manually rotate the valve to its fully closed position, then rotate it one full turn in the open direction to set the lower limit switch position. Then open the valve to its fully open position to set the upper limit switch position. This prevents the valve from failing to open electrically after being manually closed, enabling smooth opening and closing operations. However, this inadvertently causes internal leakage in the valve. Even if the electric control valve is adjusted to an ideal state, since the limit switch's action position is relatively fixed, the continuous erosion and wear of the valve by the controlled medium during operation can also cause the valve to close incompletely, leading to internal leakage.
Solution: Re-adjust the limit switch.
6. Incorrect selection of the valve type leads to cavitation corrosion, causing internal leakage in the electric control valve. Cavitation is related to pressure difference. When the actual pressure difference △P of the valve exceeds the critical pressure difference △Pc required for cavitation to occur, cavitation occurs. During cavitation, the collapse of bubbles releases enormous energy, causing significant damage to throttling components such as the valve seat and valve core. Under cavitation conditions, most valves can only operate for three months or even shorter periods, resulting in severe cavitation corrosion of the valve, causing valve seat leakage rates as high as 30% or more of the rated flow rate, which is irreparable. Therefore, electric valves for different applications have specific technical requirements, and it is crucial to select electric control valves appropriately based on the system process flow.
Solution: Implement process improvements and select multi-stage pressure-reducing or sleeve control valves.
7. Media erosion and internal leakage caused by aging of electric regulating valves. After electric regulating valves are properly adjusted and operated for a certain period of time, due to valve cavitation, media erosion, wear between the valve core and seat, and aging of internal components, issues such as excessive valve travel and incomplete valve closure may arise, leading to increased leakage. Over time, internal leakage in electric regulating valves will become increasingly severe.
Solution: Re-adjust the actuator and perform regular maintenance and calibration.
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