Bellows Seal Valve Guide
How a welded metal bellows eliminates the stem leak path for toxic, flammable, and high-purity service — and where to use bellows seal globe and gate valves.
In a conventional valve, the stem passes through gland packing that can leak over time — a problem for toxic, flammable, or high-value media. A bellows seal valve replaces that leak path with a flexible, hermetically welded metal bellows that forms a positive seal around the stem, achieving near-zero fugitive emissions and meeting strict environmental limits.
How a Bellows Seal Works
- A multi-ply or formed metal bellows is welded to the stem at one end and the bonnet at the other
- As the stem strokes, the bellows flexes (compresses/extends) while staying hermetically sealed
- A secondary backup gland packing provides a safety seal if the bellows is ever compromised
- Result: essentially zero stem leakage — typically < 50 ppmv per ISO 15848-1
- Common in globe and gate patterns; materials include SS316L, Inconel, and Hastelloy bellows
Frequently Asked Questions
What is a bellows seal valve?
A bellows seal valve uses a welded metal bellows around the stem instead of (or in addition to) gland packing, creating a hermetic barrier that prevents the process fluid from leaking along the stem — ideal for toxic, flammable, and high-purity media.
What emission standards do bellows seal valves meet?
Properly designed bellows seal valves meet fugitive-emission standards such as API 622, API 624, and ISO 15848-1 (often to the tightest Class A/BH leakage levels), supported by a backup packing as a secondary seal.
Where are bellows seal valves used?
They are used for toxic, carcinogenic, flammable, radioactive, or high-purity fluids and in heat-transfer/thermal-oil, hydrogen, and high-vacuum systems where stem leakage is unacceptable.
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