Managing Stagnation, Blockage, and Leakage in Control Valves

Managing Stagnation, Blockage, and Leakage in Control Valves

Ensuring the smooth and efficient operation of control valves is crucial for maintaining optimal performance in various industrial processes. However, issues such as valve stagnation, blockage, and leakage can disrupt system functionality and compromise overall productivity. Implementing effective preventive measures is essential to mitigate these challenges and uphold the reliability of control valve systems. Let's explore methods to prevent blocking in control valves and solutions for addressing valve leakage.

Methods to Prevent Blocking in Control Valves

(1) Cleaning Procedure: Blockages caused by welding slag, rust, or debris in the throttle port and guiding parts can lead to strain, scratches, and sealing surface damage. This issue is common during initial system operation or after overhauls. In such cases, the valve must be disassembled for cleaning, removing any debris and repairing sealing surface damage if necessary. Flushing the balance hole and pipeline is also recommended before commissioning.

(2) External Flushing: When solid particles in the media cause blockages in the throttle port or guiding parts, external flushing with gas or steam through the valve cover plug can clear the obstruction without moving the valve, restoring normal operation.

(3) Pipeline Filter Installation: To prevent blockages in small-diameter control valves, especially ultra-small flow valves, installing a filter before the valve can ensure smooth passage of the medium, particularly when dealing with media prone to precipitation.

(4) Increasing Throttle Gap: Adjusting the throttle clearance or changing the throttle parts' design, such as using open window configurations or plunger-shaped spools, can help prevent blockages caused by solid particles or debris in the medium.

(5) Media Flushing: Utilizing the medium's own scouring energy to remove precipitates and blockages can enhance the valve's anti-blocking function. This can be achieved by adopting flow closed designs, streamlined valve bodies, or enhancing throttle materials' resistance to scouring.

(6) Straight-through to Angle Conversion: Replacing straight-through valves with angle valves can reduce blockages by improving flow dynamics and minimizing dead zones where media precipitation occurs. Angle valves offer better scouring performance and streamlined designs, making them less prone to blockages compared to straight-through valves.

Solutions for Valve Leakage

(1) Sealing Grease Application: Improving valve stem sealing performance can be achieved by applying sealing grease to the valve, especially if it was not originally used.

(2) Packing Enhancement: To enhance the sealing performance of the valve stem, increasing the packing material can be considered. However, simply adding more layers of packing may not yield significant improvements.

(3) Graphite Packing Replacement: Replacing PTFE packing with flexible graphite packing can extend the service life of the valve, especially when operating temperatures fluctuate significantly. Some facilities opt to switch all PTFE packing to graphite packing for better performance and longevity, although this change may come with certain challenges, such as initial crawling issues.

(4) Flow Direction Adjustment: In situations where sealing at P1 is more challenging due to higher pressure differentials, changing the flow direction to have P2 at the stem end can be more effective, particularly for high-pressure and differential pressure valves like bellows valves.

(5) Lens Pad Sealing: Replacing plane seals with lens pad sealing can provide better sealing performance, especially under high temperatures and pressures, improving leakage issues at upper and lower cover seals and valve seat connections.

(6) Gasket Replacement: Substituting asbestos sheet gaskets with alternatives like winding gaskets or "O" rings can enhance sealing performance and longevity, particularly at high temperatures, where traditional gaskets may fail to prevent leakage. Many facilities have already adopted these newer gasket materials for improved reliability.