Steam Air Vent Valve -- Thermostatic Bimetallic WCB
Self-Acting Thermostatic Air Vent for Steam System Start-Up and Operation
Document No.SV-DS-VNT-001
RevisionRev A
DateMay 2026
ManufacturerSupreme Valves India, Ahmedabad, Gujarat, India
This datasheet covers thermostatic bimetallic air vent valves in WCB for automatic removal of air and non-condensable gases from steam systems during start-up and steady-state operation.
Technical Specifications
| Parameter | Specification |
|---|
| Size Range | DN15 to DN50 (1/2" to 2") |
| Pressure Rating | PN40 / Class 300 / 50 bar max operating |
| Body Material | WCB carbon steel or CF8M (SS316) |
| Thermostatic Element | Bimetallic strip stack, calibrated for specific steam saturation temperature |
| Valve Plug / Seat | SS316 + Stellite 6 overlay |
| Temperature Range | Element calibrated -20°C to +300°C (standard); higher on request |
| Operating Principle | Bimetallic element opens cold, closes at calibrated temperature below steam saturation |
| End Connections | Screwed NPT / BSPT, socket weld, flanged |
| Discharge Capacity | Air: 20 to 500 m³/h depending on size and differential pressure |
| Features | Self-acting, start-up air venting, calibrated bimetallic element, renewable seat |
Materials of Construction
| Component | Material |
|---|
| Body | WCB carbon steel, investment cast, machined seat bore and bimetallic chamber |
| Bonnet | WCB bolted bonnet with bimetallic element retention and adjustment screw |
| Bimetallic Element | Nickel-iron bimetallic strip stack, factory-calibrated for specific closing temperature |
| Valve Plug | SS316 with Stellite 6 overlay on seating face for erosion resistance |
| Seat | Integral WCB with Stellite 6 hard facing; replaceable seat ring optional |
| Stem / Guide | SS316 stem with upper guide bushing for plug centration |
| Spring | SS304 compression spring maintaining plug-to-bimetallic contact |
| Gaskets | Spiral-wound SS316 + graphite for body/bonnet joint |
Testing & Inspection
| Test | Requirement |
|---|
| Test Standard | ISO 7842 / EN 26948 cold water test |
| Certification | CE, ISO 9001, IBR |
Applicable Standards
| Standard | Description |
|---|
| Design Standard | ISO 6552 / EN 26704 |
Notes
- Bimetallic calibration temperature must be specified at order; standard is 10°C below steam saturation at operating pressure.
- Bimetallic element cannot be field-calibrated; if steam pressure changes significantly, replace element with correctly calibrated unit.
- For superheated steam above 350°C, specify CF8M (SS316) body and high-temperature bimetallic alloy (Inconel / Monel stack).
- Air vent must be installed at highest points of steam system where air and non-condensables naturally collect; avoid low points.
- Discharge piping from air vent must be routed to safe location; do not discharge into confined spaces or near electrical equipment.
