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As the final barrier of protection for pressure vessels, the safety valve plays a vital role in medical sterilization and laboratory equipment. This article provides a systematic introduction to the working principles, technical specifications, and management standards of safety valves to help users ensure safe equipment operation.
1. Core Functions and Importance
The autoclave safety valve is an automatic pressure relief device that performs three critical functions:
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Automatic Release: It automatically opens to release pressure when the internal pressure exceeds a set threshold (typically 0.14-0.16 MPa).
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Explosion Prevention: In emergencies, such as a temperature control system failure, it prevents the pressure vessel from exploding due to overpressure.
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Regulatory Compliance: As a mandatory safety component for special equipment, its compliance is directly related to the legal operation of the entire sterilization system.
According to safety regulations for pressure vessels (such as TSG 21-2016 or equivalent international standards), all autoclaves with a working pressure of ≥0.1 MPa must be equipped with a compliant safety valve. In medical institutions, the performance of these valves directly impacts operational safety.
2. Working Principle (Spring-Loaded Type)
Taking the most common spring-loaded safety valve as an example, its operation cycle consists of four stages:
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Stage 1: Sealing (Normal Operation) When the autoclave pressure is normal, the pre-tightening force of the spring keeps the valve disc tightly pressed against the valve seat. The valve remains closed, ensuring a sealed environment for sterilization.
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Stage 2: Simmering (Critical Point) As pressure rises to approximately 90% of the set pressure, the valve disc begins to lift slightly. A faint hissing sound may occur, indicating the system is approaching its pressure limit.
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Stage 3: Discharge (Popping) When pressure reaches 110% of the set pressure, the valve opens fully. High-temperature steam is discharged rapidly through the outlet. Crucially, the discharge capacity in this stage must exceed the autoclave’s maximum steam generation rate to effectively lower pressure.
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Stage 4: Reseating (Closing) When the pressure drops to the reseating pressure (usually 85% of the set pressure), the spring force overcomes the steam pressure, pushing the disc back onto the seat. The system reseals.
The entire process relies on the mechanical balance between steam pressure and spring force, requiring no external power source. This mechanical reliability is why it serves as the “last line of defense.”
3. Key Performance Parameters
A qualified safety valve must meet strict technical indicators:
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Set Pressure Accuracy: The error margin should be controlled within ±0.005 MPa. (Medical institutions are advised to calibrate valves every 6 months).
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Sealing Performance: No visible leakage should occur under a bubble test at 90% of the set pressure.
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Discharge Capacity: The steam discharge rate in the fully open state must be ≥ 1.1 times the maximum steam generation of the autoclave.
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Blowdown (Reseating Difference): The difference between opening and closing pressure should be ≤10% of the set pressure to avoid frequent “chattering” (rapid opening and closing).
For medical and laboratory autoclaves, it is recommended to use all-stainless steel valves equipped with a manual test lever. Ensure the product meets international standards (such as ISO 4126).
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Warning: Never adjust the spring tension yourself or replace a specialized safety valve with a common valve.
4. Maintenance and Management
To ensure the safety valve is always in “combat-ready” condition, a systematic maintenance routine is required:
Routine Inspections
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Weekly: Manually pull the test lever (when there is slight pressure) to check the flexibility of moving parts.
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Monthly: Check if the discharge pipe/port is unobstructed.
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Before Each Use: Inspect the valve body for signs of rust or leakage.
Periodic Calibration
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General Use: Calibrate at least once a year.
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Medical Use: Recommended every 6 months.
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Note: Calibration requires a precision pressure gauge (Class 0.4) and a dedicated test bench. Always keep calibration records.
Troubleshooting
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Leakage: Grind the sealing surface or replace the valve disc.
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Failure to Open: Check if the spring is rusted or stuck.
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Chattering (Frequent hopping): Check for resistance in the discharge piping.
Lifecycle Management
The normal service life of a safety valve is generally 5 years. It must be replaced upon expiration. For critical medical sterilization equipment, adopting a dual safety valve design (redundancy) is an effective way to enhance safety.
Conclusion
Although the safety valve is a small component, it is critical for safety. Users must recognize its importance and establish a sound management system. Only by combining standardized operation, regular maintenance, and strict monitoring can we ensure the safe operation of the sterilization system.