Valve leakage is a common fault problem in industrial systems, which directly affects equipment safety and operating efficiency. The following are the main causes of valve leakage and the corresponding solutions, classified by leakage type:
External leakage (external leakage of the valve body)
A. Leakage at the packing (external leakage of the valve, the proportion of the packing is the largest)
Reasons:
1. The packing is not selected correctly, it is not resistant to the corrosion of the medium, and it is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;
2. The packing is not installed correctly, there are defects such as small instead of large, poor spiral winding joints, tight top and loose bottom;
3. The packing has exceeded the service life, has aged, and lost its elasticity;
4. The valve stem is not accurate, with defects such as bending, corrosion, and wear;
5. The number of packing turns is insufficient, and the gland is not tightened;
6. The gland, bolts, and other parts are damaged, making the gland unable to be tightened;
7. Improper operation, excessive force, etc.;
8. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, causing the valve stem to wear and the packing to be damaged.
Solution:
1. The material and type of packing should be selected according to the working conditions;
2. The packing should be installed correctly according to relevant regulations. The packing should be placed and tightened one by one, and the joint should be 30℃ or 45℃;
3. The packing that has been used for a long time, aged, or damaged should be replaced in time;
4. The valve stem should be straightened and repaired after bending and wear, and the seriously damaged ones should be replaced in time;
5. The packing should be installed according to the specified number of turns, the gland should be tightened symmetrically and evenly, and the gland should have a pre-tightening clearance of more than 5mm;
6. Damaged glands, bolts and other parts should be repaired or replaced in time;
7. The operating procedures should be followed. Except for the impact handwheel, it should be operated with uniform speed and normal force;
8. The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; if the gap between the gland and the valve stem is too large, it should be replaced.
B. Leakage at the valve body/flange connection
- Causes:
- Flange bolts are loose or unevenly stressed;
- Sealing gaskets are aged (such as rubber gaskets hardened at high temperature), corroded or insufficiently thick;
- Valve body casting defects (sand holes, cracks) or corrosion perforation.
- Solution:
- Re-tighten the bolts: apply force evenly in diagonal order to avoid bias;
- Replace gaskets: select metal spiral wound gaskets, polytetrafluoroethylene gaskets, etc. according to the medium;
- Repair the valve body: small cracks can be repaired by welding, and severe corrosion requires replacement of the valve.
C. Closing parts fall off and cause leakage
Causes:
- Poor operation, causing the closing parts to get stuck or exceed the top dead center, and the connection is damaged and broken;
- The closing parts are not firmly connected, loose and fall off;
- The material of the connection parts is not selected, which cannot withstand the corrosion of the medium and mechanical wear. - Solution: - Correct operation, do not use too much force to close the valve, do not open the valve beyond the top dead center, and the hand wheel should be reversed slightly after the valve is fully opened; - The connection between the closing part and the valve stem should be firm, and there should be a stopper at the threaded connection; - The fasteners used to connect the closing part and the valve stem should withstand the corrosion of the medium and have a certain mechanical strength and wear resistance.
Internal leakage (the medium still flows after the valve is closed)
A. Sealing surface damage
- Reasons: - The medium contains solid particles that scour the sealing surface (such as steam cavitation and mud valve wear);
- Chemical corrosion (such as chloride ion corrosion of stainless steel valve seats);
- High temperature causes deformation of soft sealing materials (such as PTFE). - Solution:
- Grind the sealing surface: Use special grinding paste to repair minor scratches;
- Replace the valve seat/valve core: Replace with carbide (such as tungsten carbide) seals when seriously damaged;
- Upgrade the material: Use Hastelloy or Monel valves for corrosive media.
B. Foreign matter stuck - Cause:
- Pipeline welding slag, rust and other impurities stuck between the valve seat and the valve core;
- Medium crystallization (such as urea solution solidified at low temperature).
- Solution:
- Flush the valve: Disassemble the valve to remove foreign matter, and thoroughly purge the pipeline before installation;
- Install a filter: Install a Y-type filter in front of the valve to intercept impurities;
- Heat preservation and heating: Add steam heating to valves with easy-to-crystallize media.
C. Insufficient thrust of actuator
- Cause: - Insufficient air pressure of pneumatic actuator (such as pressure reducing valve failure);
- The torque setting of electric actuator is too small or the power supply voltage is unstable;
- The valve design pressure difference is too large, exceeding the load capacity of the actuator.
- Solution:
- Check the gas source/power supply: ensure that the gas source pressure is ≥0.4MPa and the voltage fluctuation is ≤±10%;
- Adjust the torque: recalibrate the actuator thrust and replace the actuator with a larger specification if necessary;
- Multi-stage pressure reduction: multi-stage throttle valve or angle valve is used for high pressure difference conditions.
Special leakage scenarios
A. High temperature valve leakage
- Countermeasures:
- Use a valve cover with heat sink or an extended valve stem design to reduce the packing temperature;
- Use flexible graphite packing or metal bellows seal (completely isolate the medium).
B. Leakage of ultra-low temperature valves (LNG working conditions)
- Countermeasures:
- The valve body is made of austenitic stainless steel with cryogenic treatment process;
- The sealing surface is welded with cobalt-based alloy (such as STL6) to prevent low-temperature brittle cracking.
Preventive maintenance suggestions
A. Regular inspection:
- Use infrared thermometer to monitor abnormal temperature of stuffing box (friction overheating);
- Use ultrasonic leak detector to locate small leak points.
B. Lubrication management:
- Regularly apply high-temperature grease (such as molybdenum disulfide) to the valve stem;
- Replace the lubricating oil of the worm gear mechanism of the electric actuator every six months.
Summary
Valve leakage needs to be handled according to the specific type (external leakage/internal leakage), medium characteristics and working conditions. In an emergency, temporary plugging (such as fixture glue injection sealing) can be used, but it is necessary to shut down and repair it as soon as possible. In the selection stage, priority should be given to leak-proof structures such as fully welded valve body and double seal design to reduce the risk of failure from the source.
