Boiler Safety Valve Guide: Structure, Working Principle, and Critical Protection Rules

The moment a boiler exceeds its allowable working pressure, it becomes a potential explosive device. The safety valve acts as the final protective barrier, capable of releasing excess pressure within milliseconds to prevent catastrophic failure. This article provides an in-depth breakdown of its structure, working mechanism, life-saving functions, selection rules, and mandatory maintenance procedures.

1. Structural Breakdown: Four Precision-Engineered Core Components

2. Operating Principle: A Three-Stage Pressure-Release Process

Sealing Stage

When boiler pressure is below 95% of the lift-off pressure, the spring force keeps the disc tightly sealed, preventing any leakage.

Lift-Off Stage

When internal pressure reaches approximately 1.04× the working pressure (per TSG standards), steam force overcomes spring tension, causing the valve to pop open in under 0.1 seconds.

Reseating Stage

Once pressure drops to 94%–98% of the working pressure, the disc closes again. Incorrect reseating range may lead to repeated popping or excessive discharge.

3. Core Safety Functions: More Than Just Pressure Relief

Emergency Overpressure Release

The safety valve releases pressure before a boiler reaches a critical explosive state, with a discharge capacity equal to or greater than the rated evaporation capacity.

Pressure Stabilization

Small valve vibrations during early instability provide an audible early warning signal when pressure fluctuates above 5%.

Last Line of Defense

If low-water cutout, pressure gauges, or control systems fail, the safety valve remains the only safeguard preventing an explosion.

4. Safety Valve Types: Selecting the Wrong One Creates Hidden Risks

Selection Rules

• Steam boilers must use full-lift safety valves (lift ≥ 1/4 of throat diameter).

• Hot-water boilers must use low-lift types to avoid excessive water discharge.

5. Maintenance Protocol: Three Steps That Determine Life or Death

Daily

• Perform manual lift tests to prevent disc sticking.

Monthly

• Check discharge pipes for blockage.

• Diagnose leaks: pipe temperature >60°C or audible hissing indicates a problem.

Annual Mandatory Inspection

• Verify lift-off pressure (error ≤ ±1%).

• Confirm reseating pressure ≥ 94% of working pressure.

• Conduct sealing test (no leakage at 90% of working pressure).

6. Prohibited Practices: Actions That Lead Directly to Accidents

• Increasing lift-off pressure without authorization.

• Replacing safety valves with ordinary valves.

• Operating with overdue or fatigued springs (replace after 5 years).

Mandatory Compliance Requirements

• Each boiler must be equipped with two independently installed safety valves.

• Calibration certificates must be archived permanently.

• New boilers must adopt intelligent safety valves with pressure sensing and remote alarms.

Conclusion

Overpressure can occur in an instant, and a malfunctioning safety valve leaves no second chance. If your safety valve is leaking, stuck, or overdue for inspection, shut down the boiler immediately. Contact our technical team for professional diagnostics and replacement solutions.