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一. External Leakage (Leakage from the Valve Body Exterior)

A. Leakage at the Packing Area (External valve leakage, with the packing area accounting for the largest proportion)

Causes:

1. Inappropriate packing selection, lacking resistance to medium corrosion or unable to withstand high pressure, vacuum, high temperature, or low temperature conditions;

2. Incorrect packing installation, including using undersized packing, poor spiral winding joints, or uneven tightening (tight at top, loose at bottom);

3. Packing exceeding its service life, having aged and lost elasticity;

4. Inadequate valve stem precision, exhibiting bending, corrosion, or wear;

5. Insufficient packing layers, with the gland not sufficiently tightened;

6. Damage to the gland, bolts, or other components preventing proper gland compression;

7. Improper operation, such as excessive force application;

8. Misaligned gland, with excessive or insufficient clearance between gland and valve stem, causing stem wear and packing damage.

Resolution:

1. Select packing material and type according to operating conditions;

2. Install packing correctly per relevant regulations; gland packing must be compressed coil by coil, with joints at 30° or 45° angles;

3. Replace packing promptly if it has been in use excessively long, aged, or damaged;

4. Straighten and repair bent or worn valve stems; replace severely damaged stems immediately;

5. Packing must be installed to the specified number of turns. The gland cover should be tightened symmetrically and uniformly, with the gland sleeve maintaining a preload clearance of at least 5mm;

6. Damaged gland covers, bolts, and other components must be promptly repaired or replaced;

7. Operating procedures must be adhered to. Except for impact-type handwheels, operation should be performed at a uniform speed and with normal force;

8. Packing gland bolts must be tightened evenly and symmetrically. Should the clearance between the gland and valve stem be insufficient, it must be appropriately increased; should the clearance be excessive, the gland must be replaced.

B. Leakage at Valve Body/Flange Joints 

  Causes: 

1．Loose or unevenly tensioned flange bolts; 

2.Aged gaskets (e.g., rubber gaskets hardened by high temperatures), corrosion, or insufficient thickness; 

3.Casting defects in valve body (sand holes, cracks) or corrosion perforation.

Resolution: 

1.Retighten bolts: Apply force evenly in a diagonal sequence to avoid uneven pressure distribution; 

2.Replace gasket: Select appropriate material such as metal-wrapped gaskets or PTFE gaskets based on the medium; 

3.Repair valve body: Minor cracks may be welded; severely corroded valves require replacement.

C. Leakage due to seal detachment

Causes: 

1.Improper operation causing seal jamming or exceeding top dead centre, resulting in joint damage or fracture; 

2.Insecure seal connection leading to loosening and detachment; 

3.Inappropriate joint material selection, unable to withstand medium corrosion or mechanical wear.

Solutions:

1.Operate correctly: do not apply excessive force when closing; do not exceed the top dead centre when opening; after fully opening, slightly reverse the handwheel;

2.Ensure secure connection between the closing member and valve stem; use anti-backing devices at threaded joints;

3.Fasteners connecting the closing member to the valve stem must withstand medium corrosion and possess adequate mechanical strength and wear resistance.

二. Internal Leakage (Media Flow Persists After Valve Closure) 

A. Sealing Surface Damage 

Causes: 

1.Media containing solid particles eroding the sealing surface (e.g., steam carrying water causing cavitation, slurry valve wear); 

2.Chemical corrosion (e.g., chloride ion corrosion of stainless steel seats); 

3.High temperatures causing deformation of soft sealing materials (e.g., PTFE). 

Solutions: 

1.Grind sealing surfaces: Repair minor scratches using specialised grinding paste; 

2.Replace seat/plug: Substitute with hard alloy (e.g., tungsten carbide) seals for severe damage; 

3.Upgrade materials: Switch to Hastelloy or Monel alloy valves for corrosive media.

B. Foreign Object Obstruction 

Causes: 

1.Pipeline slag, rust, or other impurities lodged between the valve seat and plug; 

2.Medium crystallisation (e.g., urea solution solidifying at low temperatures). 

Solutions: 

1.Flush the valve: Dismantle the valve to remove obstructions, thoroughly purge the pipeline before reassembly; 

2.Install a filter: Fit a Y-strainer upstream to intercept contaminants; 

3.Apply insulation and tracing: Install steam tracing on valves handling crystallising media.

C. Insufficient Actuator Thrust 

Causes: 

1.Inadequate pneumatic pressure in pneumatic actuators (e.g., pressure reducing valve failure); 

2.Torque setting too low or unstable power supply voltage in electric actuators; 

3.Valve design pressure differential exceeds the actuator's load capacity.

Resolution: 

1.Inspect air supply/power source: Ensure air supply pressure ≥0.4MPa, voltage fluctuation ≤±10%; 

2.Adjust torque: Recalibrate actuator thrust; replace with larger-rated actuator if necessary; 

3.Multi-stage pressure reduction: Employ multi-stage throttle valves or angle valves for high differential pressure conditions.

三．Specialised Leakage Scenarios 

A. High-Temperature Valve Leakage 

1.Countermeasures: 

2.Employ valve bonnets with heat sinks or extended stem designs to reduce packing temperature; 

3.Select flexible graphite packing or metal bellows seals (for complete media isolation). 

B. Cryogenic Valve Leakage (LNG Service) 

1.Countermeasures: 

2.Employ austenitic stainless steel treated with cryogenic processes for the valve body; 

3.Overlay the sealing surfaces with cobalt-based alloys (e.g., STL6) to prevent cryogenic embrittlement.

四. Preventive Maintenance Recommendations 

A. Routine Inspections: 

1.Monitor packing gland temperatures for anomalies (friction overheating) using an infrared thermometer; 

2.Locate minute leakage points using an ultrasonic leak detector. 

B. Lubrication Management: 

1.Periodically apply high-temperature grease (e.g., molybdenum disulphide) to the valve stem; 

2.Replace lubricating oil in the electric actuator's worm gear mechanism every six months.