Bellow Seal Valves — Overview
Conventional gland-packed valves inevitably leak small amounts of process fluid to the atmosphere through the stem packing over time. In applications handling toxic, flammable, expensive, or environmentally regulated fluids, this fugitive emission is unacceptable. Bellow seal valves solve this problem by enclosing the stem in a flexible metal bellows that creates a hermetic, zero-leakage barrier between the process and atmosphere.
KSB’s ECOLINE bellow seal range provides both gate valves (BSGT-S for isolation) and globe valves (BSGL-S for throttling) with AISI 316 Ti titanium-stabilized stainless steel bellows. Both feature double sealing — the bellows as primary seal and conventional graphite gland packing as backup in case of bellows fatigue failure.
Product Range
ECOLINE BSGT-S — Bellow Seal Gate Valve
Bellow seal gate valve for on/off isolation where zero stem leakage is mandatory. Cast steel version (Class 150/300, 2–12") designed to API 600 with Stellite hard-faced seat and wedge. Forged steel version (Class 800, ½–2") designed to API 602. Maximum pressure limited to 80 bar for Class 800. Flanged, butt weld, socket weld, and threaded end connections available.
ECOLINE BSGL-S — Bellow Seal Globe Valve
Bellow seal globe valve for flow regulation and shut-off where zero stem emission is required. Cast steel version (Class 150/300, 2–12") designed to BS 1873 with Stellite hard-faced plug and seat. Forged steel version (Class 800, ½–2") designed to API 602. Maximum pressure limited to 80 bar for Class 800. Globe pattern provides precise throttling control for process flow regulation.
Technical Specifications
| Parameter | BSGT-S Gate (Cast) | BSGT-S Gate (Forged) | BSGL-S Globe (Cast) | BSGL-S Globe (Forged) |
|---|---|---|---|---|
| Function | On/off isolation | On/off isolation | Throttling & shut-off | Throttling & shut-off |
| Design Standard | API 600 | API 602 | BS 1873 | API 602 |
| Pressure Class | 150, 300 | 800 (max 80 bar) | 150, 300 | 800 (max 80 bar) |
| Size Range | 2–12" | ½–2" | 2–12" | ½–2" |
| Body Material | A216 WCB/WCC, A351 CF8/CF8M | A105, A182 F304/F316 | A216 WCB/WCC, A351 CF8/CF8M | A105, A182 F304/F316 |
| Bellows Material | AISI 316 Ti | AISI 316 Ti | AISI 316 Ti | AISI 316 Ti |
| Seat/Disc Hard-facing | AISI 410 + Stellite | AISI 410 + Stellite | AISI 410 + Stellite | AISI 410 + Stellite |
| Stem Material | AISI 410 | AISI 410 | AISI 410 | AISI 410 |
| Backup Packing | Graphoil | Graphoil | Graphoil | Graphoil |
| End Connection | Flanged (ASME B16.5) / Butt weld | SW (B16.11) / Threaded / BW | Flanged (ASME B16.5) / Butt weld | SW (B16.11) / Threaded / BW |
| Testing | API 598 | API 598 | API 598 | API 598 |
| Bellows Cycle Test | MSS-SP-117 | MSS-SP-117 | MSS-SP-117 | MSS-SP-117 |
Body Materials & Temperature Limits
| ASTM Grade | Type | Max Temp | Available In |
|---|---|---|---|
| A216 WCB / WCC | Cast carbon steel | 425°C | Cast gate & globe (Class 150/300) |
| A351 CF8 | Cast 304 stainless | 538°C | Cast gate & globe (Class 150/300) |
| A351 CF8M | Cast 316 stainless | 538°C | Cast gate & globe (Class 150/300) |
| A105 | Forged carbon steel | 425°C | Forged gate & globe (Class 800) |
| A182 F304 | Forged 304 stainless | 538°C | Forged gate & globe (Class 800) |
| A182 F316 | Forged 316 stainless | 538°C | Forged gate & globe (Class 800) |
Applications by Industry
Chemical & Petrochemical
Chlorine, ammonia, acids, solvents, toxic chemicals. Bellow seal prevents hazardous leakage to atmosphere. SS CF8M/F316 for corrosive media resistance.
Pharmaceutical & Food
Sterile process lines, clean-in-place systems, solvent handling. Zero emission ensures product purity and operator safety. SS construction for hygiene.
LPG & LNG
Liquefied gas handling where any leak is a fire/explosion hazard. Double sealing provides primary and backup protection. Cryogenic service capability.
Vacuum Service
Vacuum distillation, vacuum drying, vacuum packaging. Bellow seal prevents air ingress that would break vacuum. Tight shut-off in both directions.
Power Plants
Nuclear and thermal power applications where fugitive emissions must be eliminated. Bellows protects against radioactive or thermal fluid leakage.
Refineries
Hydrocarbon process isolation, hydrogen service, high-value fluid containment. Prevents product loss and environmental contamination.
Key Design Features
- Double sealing system — AISI 316 Ti metal bellows as primary seal, Graphoil gland packing as secondary backup
- Stem completely enclosed by bellows — process fluid never contacts the gland packing area during normal operation
- Bellows reduces shock load to trim parts, extending seat and disc service life
- AISI 316 Ti (titanium-stabilized) bellows material provides superior fatigue resistance and corrosion resistance compared to standard 316
- Bellows cycle life tested per MSS-SP-117 for validated fatigue performance
- Stellite hard-faced seat and disc/wedge interface for wear resistance and tight shut-off
- Available with electric and pneumatic actuators, gearboxes, and locking arrangements
- Environment protected from toxic substances — meets increasingly strict fugitive emission regulations
- Gate valve (BSGT-S) for full-bore isolation with minimal pressure drop; Globe valve (BSGL-S) for precise throttling and flow regulation