Sealing & Emission Control Systems
Stem Sealing
Bellows Seal Stem
A welded metal bellows fully encloses the stem between the disc and the packing, providing a hermetic secondary barrier so the packing is a backup, not the primary seal - the closest a rising-stem valve gets to zero fugitive emission.
How does bellows seal stem work?
The bellows flexes with stem travel while its welded metal wall stays leak-tight, isolating the process fluid from the packing gland entirely under normal operation. A conventional packing set is still fitted as a backup seal in case the bellows itself fails.
When to Use It
- Toxic, carcinogenic, or radioactive service where any stem leakage is unacceptable
- Zero-fugitive-emission specifications that exceed what live-loaded packing alone can guarantee
- High-value or hazardous fluids where a secondary packing backup is required by the safety case
Limitations
- Bellows life is finite and cycle-dependent - not suited to very high-cycle throttling duty without a qualified cycle rating
- Significantly higher cost and longer lead time than packing-only designs
- Bellows fatigue failure is a real, if rare, failure mode that must be inspected for over the valve's life
Typical MaterialsInconel; Hastelloy; Stainless steel bellows with graphite backup packing
Used OnGate ValvesGlobe Valves
Governing Standards
Related Failure Mechanisms
Related Troubleshooting Guides
Typically Specified In
Other stem sealing designs
Reviewed by Process Engineering, Vajra Industrial SolutionsDiscipline: Valve Service SpecificationLast reviewed: 20 June 2026
Connected Engineering
Failure Modes
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