1、 Common locations of valve leaks

Valve leakage mainly occurs in the following two areas:

External leakage: Leakage between the valve body and the external environment.

Valve stem sealing area: The most common leakage location is usually caused by aging or wear of the packing or sealing ring inside the packing box.

Valve body connection: gasket or seal failure at flange or threaded connection.

Valve body itself: pinholes or cracks caused by casting or welding defects.

Internal leakage: The valve cannot be fully closed, causing the medium to leak from the sealing surface.

The sealing surface between the valve seat and the valve disc (gate valve, ball valve, etc.): wear, corrosion, inclusions, or deformation.

2、 The main cause of leakage

A. Reasons for external leakage:

Sealing failure: aging, cracking, shrinkage or wear of fillers (such as graphite, polytetrafluoroethylene); Elastic seals (such as O-rings) harden or deform.

Improper installation: uneven tightening of gland bolts; Uneven pre tightening force of flange bolts; Improper threading processing.

Valve stem damage: The valve stem is corroded, scratched, or bent, causing the valve stem to be unable to tightly contact the packing.

Process condition changes: Temperature or pressure fluctuations beyond the valve design range result in thermal expansion and contraction of the valve.

B. Internal leakage cause:

Sealing surface damage: caused by solid particles (erosion, scratches) or chemical corrosion in the medium.

Foreign object interference: Foreign objects such as welding slag or rust get stuck on the sealing surface, causing the valve to be unable to fully close.

Actuator issue: Insufficient torque/thrust of the driving device (handwheel, oil cylinder, electric actuator), unable to fully close the valve.

Selection error: The valve type or sealing material does not match the medium (temperature, pressure, corrosiveness).

III. Testing method

Visual/auditory/olfactory examination: Listen for sound, smell odors, and check for condensation medium (steam leakage), frost (low-temperature medium), or dust accumulation (clean gas leakage points).

Soap liquid/bubble leak detector: the simplest and most commonly used gas leak detection method; The leakage point will form bubbles.

Ultrasonic detector: detects high-frequency sound waves generated by gas leaks; It can accurately locate the leakage point, especially suitable for high-pressure gas systems.

Infrared thermography: Identifying steam or high-temperature medium leaks through temperature differences.

Gas detector: Use specialized sensors to detect the concentration of toxic or flammable gases.

Pressure/flow testing: Rapid pressure drop or abnormal downstream flow during system pressure testing may indicate the presence of internal leaks.

IV. Handling and maintenance methods

Important safety reminder: Before performing any operation, please ensure that the system has been depressurized, emptied, isolated, and cooled down. Follow the Lock Out/Tag Out (LOTO) procedure.

External leakage:

Leakage of valve stem packing:

Minor leakage: Try to tighten the gland bolts evenly (avoid over tightening to prevent crushing the packing or jamming the valve stem).

Serious leakage: requires refilling. Remove the old packing, install the new packing correctly (e.g. staggered installation), and tighten the gland moderately.

Connection point leakage:

Flange leakage: Try tightening the bolts evenly in a cross pattern. If it is ineffective, replace the gasket.

Threaded connection leakage: Disassemble, reapply thread sealing tape or sealant, or replace the joint.

Valve body leakage: usually difficult to repair online; Usually, the entire valve needs to be replaced.

Internal leakage:

Attempt flushing/cycling: For valves that may be blocked by debris, try quickly opening and closing them a few times to flush out the debris with the medium.

Adjust or repair the actuator: Ensure sufficient cylinder pressure or electric actuator torque. For manual valves, ensure that they are fully closed.

Grinding sealing surface: Perform online or offline grinding to repair minor sealing surface damage.

Replace valve internals/seats: For severely damaged seals, replace damaged components such as valve discs and seat rings.

Replace valve: If the repair cost is too high or the valve repair cost is too high, replace the entire valve.

5、 Preventive measures

Correct selection: Choose the appropriate valve type, material, and sealing design based on the characteristics of the medium, temperature, pressure, and cycle frequency.

Correct installation: Install strictly according to the procedure to ensure alignment, cleanliness, and even tightening of bolts.

Regular maintenance:

Develop a preventive maintenance plan and regularly inspect the packing and actuators.

Regularly operate the valve (open/close) to prevent the valve stem from getting stuck.

Regular testing of critical valves (such as seat leakage testing).

Optimize operation:

Smooth operation, avoiding water hammer and sudden pressure changes.

Install an upstream filter to filter out dirty media.

The valve should be fully open or closed; Avoid being in a semi open state for a long time to prevent corrosion.

Condition monitoring: Use sensors, ultrasonic detectors, and other tools to conduct online condition monitoring of important valves, achieving predictive maintenance.

VI. Summary

The key to dealing with valve leaks lies in quickly locating the leak point, accurately determining the cause of the leak, and taking safe and effective measures. For non critical valves, simple tightening or replacement is sufficient. However, for critical process valves or valves handling hazardous media, strict maintenance or replacement plans must be developed and implemented by qualified personnel.