Sealing & Emission Control Systems
Stem Sealing
Secondary (Double) Stem Seal
A second, independent sealing element above the primary packing - often a lip seal or O-ring set - captures any emission that passes the primary seal, with a monitored port between the two for leak detection.
How does secondary (double) stem seal work?
The primary packing does the main sealing job; the secondary seal above it is a backup barrier, and the small monitoring port between the two lets a technician verify the primary seal's integrity without disturbing it or venting to atmosphere.
When to Use It
- Regulatory environments requiring demonstrable, verifiable leak detection (not just a tight seal on installation)
- Ball valve stem sealing on critical hydrocarbon or chemical service where a single seal is judged insufficient
- Complementing (not replacing) a bellows seal for defense-in-depth on the highest-consequence services
Limitations
- Adds stem length and gland complexity over a single-seal design
- The monitoring port itself must be included in the leak-test and maintenance procedure or the benefit is lost
Typical MaterialsPTFE lip seal; elastomer O-ring (service-dependent compound)
Used OnBall ValvesGate 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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