When a safety valve leaks internally, many repairers immediately lap the sealing surfaces. After lapping, the valve passes the bench test but leaks again within three months. Poor lapping technique is not always the reason. Two other factors are often ignored.The main safety valve product names of China Safety Valve Network include:,GA49H-DN20 Pulse Safety Valve,High Temperature and Pressure Fall Lift Safety Valve,Hydraulic Safety Valve,Impulse Safety Valve,Impulse Spring Safety Valve,JIS Safety Valve,Main Safety Valve,Overflow ValveOil Refining Specific Safety Valve,Pulse Safety Valve,Pilot Safety Valve,Pressure Safety Valve,Quick Switching Safety Valve,Spring Low Lift Safety Valve

1. Lapping widens the contact band

A safety valve seals through a band contact of about 1.5–3mm width. When lapping to remove scratches, it is easy to widen the band to over 5mm. Wider contact reduces sealing pressure per unit area. The valve may pass a static bench test but will leak under vibration or during operation.

2. Excessive disc guide clearance

The disc is positioned by a guide bushing. After long service, guide wear increases radial clearance. Even with perfectly lapped seats, the disc tilts when closing – one side touches first, leaving a gap on the other. A static bench test may not catch this, but dynamic service will.

Quick field check

If a lapped valve passes the bench test but leaks days after installation, suspect a wide contact band. If the valve fails to reseat after a pop or leaks periodically, suspect excessive guide clearance.

Practical rule

Do not lap every internal leak. First, check with a kerosene leak test. If no leakage, the seat is fine – inspect the guide and spring. Keep the contact band around 2mm and guide clearance under 0.1mm.

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