Y-Type Bellows Globe Valve

About Bellows Seal Globe Valve 2" - 12" (DN50 - DN300) Class 150 - 600 API 602, ISO 15848, TA-Luft, BS 1868, ASME B16.34 A216 WCB, A351 CF8M, A182 F316 Bellows seal (Inconel 625 / Hastelloy C-276) + graphite packing backup Flanged, butt weld, or socket weld ends

Why Bellows Seal Exists — Packing Alone Isn’t Enough Graphite packing does a respectable job in general service. In toxic, flammable, or hazardous media service, “respectable” isn’t good enough. Packing wears. Thermal cycling relaxes the gland. Stem friction opens micro-paths between packing rings. A valve that passes API 598 on day one can develop visible stem leakage within 18 months on a hot cycling line. Once process fluid reaches atmosphere, you’re dealing with TA-Luft violations, LDAR citations, and in the worst case, a toxic release.

A bellows seal eliminates the leak path structurally. A multi-ply metal bellows assembly welded between the stem and the bonnet creates a hermetic barrier — process fluid is contained inside the bellows, and the packing above the bellows serves as a backup seal, not the primary one. Zero stem emission to atmosphere. Not “low leakage.” Zero.

How the Bellows Actually Works The bellows is a welded multi-ply convolution — typically 2–3 plies of Inconel 625 or Hastelloy C-276. Each ply is 0.04–0.08 mm thick. The convolutions flex as the stem strokes, absorbing axial movement without rotating. When the valve opens, the bellows extends. When it closes, it compresses. The packing above the bellows never sees process pressure under normal operation — it only engages if the bellows fails, which is why the design is called “bellows primary, packing backup.”

Fatigue life is the critical spec. FLOWKS bellows are rated for ≥ 10,000 full-stroke cycles verified per ASME B31.3. In real-world throttling service where the valve might cycle 5–10 times per day, that’s 3–5 years of fatigue margin. For isolation service cycling once per week, the bellows outlasts the plant.

Material Selection — Matching the Media Inconel 625: high-temperature service up to 600°C. Resistant to oxidizing and reducing atmospheres. The default choice for steam and hot hydrocarbon service. Hastelloy C-276: aggressive chemical service — sulfuric acid, hydrochloric acid, wet chlorine gas, chlorinated organics. Where Inconel’s nickel-chromium matrix would pit, C-276’s molybdenum addition holds. 316Ti: lower-cost option for moderate corrosive service where Hastelloy is over-specified. Helium Leak Testing — Not Optional Every FLOWKS bellows seal valve undergoes 100% helium leak testing at the factory before shipment. The test pressurizes the bellows with helium and measures external leak rate with a mass spectrometer. Acceptance criteria: ≤ 1×10⁻⁶ mbar·L/s. That’s ISO 15848-1 AH class — the tightest fugitive emission classification in the standard.

Why helium? It’s the smallest inert molecule — if helium can’t escape, nothing in your process stream can. A valve that passes helium testing at 10⁻⁶ won’t leak VOCs, won’t leak steam, won’t leak hydrogen. The test is destructive to defective units