Understanding Bellow Seal Globe Valves
A bellow seal globe valve is a specialized shut-off valve designed to eliminate stem leakage in critical applications. Unlike traditional packed globe valves, it uses a metallic bellows assembly welded to both the stem and valve body, creating a hermetic seal. This design is essential for handling toxic, corrosive, or high-purity media where fugitive emissions are unacceptable.
Key Components of Bellow Seal Globe Valves
1. Bellows Assembly
- Material: Stainless steel (SS316/316L), Inconel 625, or Hastelloy C276
- Design: Multi-ply convolutions (8-12 layers) for 10,000+ cycle durability
- Function: Compresses/extends during valve operation while maintaining seal integrity
2. Valve Body
- Pressure Rating: Class 150 to Class 2500 (ANSI/ASME B16.34)
- End Connections: Flanged (RF/RTJ), socket weld, or buttweld
- Temp Range: -196°C to 550°C (cryogenic to high-heat)
3. Stem & Disc
- Integral forged stem-disc assembly for alignment
- Surface hardening (Stellite 6 coating) for abrasion resistance
4. Secondary Seal (Backup)
- Graphite packing rings below bellows as fail-safe
How Does a Bellow Seal Globe Valve Work
Step 1: Opening the Valve
When the handwheel is rotated counterclockwise:
- The stem rises, lifting the disc from the seat
- Bellows compress axially, maintaining seal integrity
Step 2: Closing the Valve
Clockwise rotation:
- Stem forces disc against seat, stopping flow
- Bellows extend to original length
Step 3: Leakage Prevention
Double sealing action:
- Primary seal: Bellows block stem leakage path
- Secondary seal: Graphite packing (API 622 compliant)
Advantages Over Standard Globe Valves
| Feature | Bellow Seal Globe Valve | Packed Globe Valve |
|---|---|---|
| Stem Leakage | Zero fugitive emissions (ISO 15848-1 TA-Luft) | Up to 500 ppm leakage |
| Maintenance | No packing replacement needed | Annual packing maintenance |
| Applications | Hazardous, high-purity, vacuum systems | General water/steam services |
Industrial Applications
1. Chemical Processing
- Chlor-alkali plants (chlorine gas containment)
- Pharmaceutical API production
2. Oil & Gas
- HF alkylation units
- LNG cryogenic transfer (-162°C)
3. Power Generation
- Boiler feedwater isolation
- Steam turbine bypass systems
Selection Criteria
1. Bellows Type
- Forged Bellows: High-pressure (ASME Class 1500+)
- Welded Bellows: Corrosive media (electropolished finish)
2. Flow Characteristics
- Equal percentage vs. linear flow for control applications
3. Certifications
- NACE MR0175 for sour service
- PED 2014/68/EU for European markets
Top China Bellow Valve Manufacturers
Chinese manufacturers like NSW Valve Manufacturer offer:
- API 602/BS 1873 compliant designs
- 30% cost savings vs. European brands
- Custom bellows testing (helium leak detection)
Maintenance Best Practices
- Annual bellows inspection for fatigue cracks
- Stem lubrication with high-temperature grease
- Avoid over-torquing (max 50 Nm for DN50 valves)
Post time: Apr-10-2025