Troubleshooting Manual: Root Causes And Solutions For Leakage And Blockage Of Diaphragm Valves At Bottom Of Manual Water Tanks

I. Root and solutions to leakage
(I) Internal Leakage (Valve Not Closing Tightly)
Damage to Sealing Surface
Reason: Particulate matter in media (such as sand, solder slag) corrode the seal, or acidic media corrode the sealing surface, causing damage. For example, a dairy company suffered an internal leakage when sand particles got stuck between the valve seat and the disc because there was no filter.
Solutions:
Remove the valve and manually grind the metal sealing surface with a polished material to repair minor scratches or dents.
Replace the soft sealing gasket (e.g. EPDM, PTFE) to ensure material is compatible with the medium.
Install a Type Y filter in front of the valve to trap impurities.
Aging or wear of the seal
Reason: rubber diaphragm after long-term use aging, cracking, or the metal sealing surface due to frequent opening and closing and wear.
Solutions:
Replace the diaphragm regularly (recommended every 1-2 years) and choose a temperature-resistant and pressure-resistant material (such as silicone rubber resistant to 150°C). Repair worn Repair worn metal sealing surfaces by welding or replacing the entire valve seat.
Valve not fully closed
Reasons: Insufficient operating torque (e.g., handwheel not tightening) or valve stem thread jamming resulting in incomplete closure.
Solution: Use a torque wrench to ensure the handwheel is completely closed to avoid skidding.
Check valve stem thread for damage; replace valve stem or nut if necessary.
Impurities in valve core/seat
Reason: Pipeline surface between the appearance of rust, scale and other impurities.
Solution: Remove valve to clean impurities on sealed cover.
Install magnetic filters to absorb adsorb metal impurities such as iron filings.
(II) External leakage (leakage of valve body or connection)
valve stem leakage (through stuffing box)
Reasons: Filling (e.g., graphite, PTFE) wear or age, or scratches on valve stem cause seal failure.
Solution: Tighten stuffing cover bolts, but avoid overtightening to prevent valve stem from jamming.
Replace packagings with media corrosion resistant materials (e.g. graphite packaging for high temperature applications). Repair stem scratches; replace valve stem if necessary.
Leak in valve body or flange connection
Reasons: Insufficient flange bolt preload, damaged gasket, or incorrect gasket selection (e.g., non-use of a metal gasket in high temperatures).
Solution: Tighten the bolt again and apply force evenly in diagonal order.
Replace temperature and pressure resistant gaskets (e.g. spiral winding gaskets, PTFE gasket).
Repair valve body cracks by welding (safety assessment required); if serious, replace valve.
Welding leakages
Reasons: defects in castings or poor welding lead to welding crackings.
Solution: Close valve and replace valve to avoid defective operation.
Non-destructive testing of welds (such as ultrasonic testing) to ensure welding quality.
ii. Causes of congestion and solutions
(I) Valve stem lifting malfunction (jammed and motionless).
Threaded damage
Reason: Excessive operation (e.g. use of extension lever) leads to valve stem or nut threads damage.
Solution: Standardize operation to avoid forced opening and closing.
Replace damaged valve stem or nut and repair thread. Lubrication Failure
The reason: the lubricating oil dries out, is contaminated or fails, causes the increased frictional resistance to increase.
Solution: Use high-temperature, dielectricresistant grease (such as molybdenum disulfide grease).
Establish a regular lubrication maintenance schedule (quarterly lubrication).
Valve Stem Deformation
Causes: External shock, improper installation or overload causing valve stem to bend.
Solution: Replace bent valve stem to ensure vertical installation.
Avoid running the valve in a partially open state for long periods of time to reduce the pressure on the valve stem.
Coarse or too tight surface
Cause: Threaded surface finish or excessive machining tolerances, resulting in insufficient assembly clearance.
Solution: Repair or replace rough threaded surfaces.
Ensure proper tolerances during manufacturing/ maintenance and check rotation flexibility during assembly.
Nut Tilting or Improper Material Matching
Reasons: Improper nut installation or incompatibility of valve stem and nut materials (for example, both are made of ordinary carbon steel and are prone to adhesion and wear).
Solution: nut installation correctly to ensure coaxial alignment with valve stem.
valve stem is made of stainless steel, such as 316L, and the nut is made of bronze or nickel-based alloys for good friction resistance.
Corrosion of media or External Contamination
Cause: Corrosive media corrodes stem threads, or dirt accumulates on exposed valves, leading to rust.
Solution: Choose corrosion resistant materials (such as fluorinated polymerlined valves for acidic media).
Wash the exposed parts of the valve stem regularly and apply rust oil.
III. Prevention and Maintenance Recommendations
Strictly judged.
Match valve material according to the characteristics of the medium (temperature, pressure, corrosion). Chlorine applications, for example, require Hastelloy valve bodies chlorine applications.
Priority is given to full-bore designs to reduce debris and reduce blockage risk.
Regular maintenance
Quarterly check for wear and tear of sealing cover and annual pressure sealing tests.
Establish a lubrication maintenance system to ensure smooth valve stem movement.
Standardized Operation
Avoid the valve being partially open for long periods of time, and do not close it with too much force.
Check the condition of the valve before operation to ensure that no foreign object is blocking it.
Technology upgrade
Install a smart valve diagnostics system to monitor leakage signals in real time and provide jamming warnings. For high frequency opening and closing, consider upgrading to an electric diaphragm valve to reduce human error.