Bellows Seal Valve Series

What is a bellows seal valve and why is it used?

A bellows seal valve uses a fully welded metallic bellows (typically SS316L or Inconel 625) as the primary stem seal, completely eliminating the conventional packed gland (stuffing box) that is the primary source of stem leakage in standard valves. The bellows flexes with stem movement while maintaining a hermetic seal. It is used for: (1) Hazardous/toxic media (chlorine, phosgene, mercury); (2) Fugitive emission compliance (ISO 15848, EPA Method 21); (3) High-value media (expensive chemicals, pharmaceutical ingredients); (4) High-temperature thermal cycling where packing degrades rapidly.

What is the expected service life of a bellows seal valve?

The service life of a bellows seal valve depends on: (1) Number of stem cycles — TANGGONG bellows are tested to 10,000+ cycles; (2) Temperature cycling — thermal expansion/contraction fatigue; (3) Pressure fluctuations; (4) Bellows material — Inconel 625 lasts 3–5× longer than SS316L in corrosive service. Typical service life: 5–10 years for chemical service, up to 20 years for stable temperature/pressure conditions. Every TANGGONG bellows valve includes a backup packing gland for extended service after bellows end-of-life.

What materials are TANGGONG bellows made from?

TANGGONG bellows are manufactured from: (1) SS316L (standard) — for general hazardous chemical service; (2) Inconel 625 (premium) — for chlorine, acidic chlorides, and high-temperature service; (3) Monel 400 — for hydrofluoric acid and fluorine gas; (4) AM350 (high-strength) — for high-cycle applications. All bellows are 100% helium-leak tested (≤ 1×10⁻⁶ mbar·L/s) before assembly. Bellows wall thickness is optimized per EN 1231 / EJMA standards.

Is a bellows seal valve fire-safe?

Yes. TANGGONG bellows seal valves are designed with a secondary fire-safe packing gland behind the bellows. In the event of fire, if the bellows is damaged, the secondary packing provides the seal to prevent external leakage. The valve body and bonnet are designed per API 607 / API 6FA fire-safe requirements. TANGGONG bellows seal valves have passed third-party fire-safe testing.

How does a bellows seal compare to a packed gland seal?

Packed gland valves: (1) Continuous stem leakage of 50–1000 ppm VOC (volatile organic compounds); (2) Require periodic packing adjustment/tightening; (3) Packing degrades in thermal cycling; (4) Lower initial cost. Bellows seal valves: (1) Zero stem leakage (≤ 0.01 ppm VOC); (2) No maintenance for stem seal (only backup packing); (3) Withstands thermal cycling; (4) Higher initial cost but lower TCO (total cost of ownership) due to eliminated fugitive emissions penalties and reduced product loss. ROI is typically 12–24 months for continuous process plants.