Spirax Marshall BPT 21 / AV 21 Balanced Pressure Steam Trap & Air Vent

The Spirax Marshall BPT 21 / AV 21 is a dual-function balanced pressure thermostatic steam trap and automatic air vent engineered to purge cold air and non-condensable gases from industrial steam loops. By continuously discharging air on start-up and expelling cool condensate, it prevents thermal air binding, improves heat transfer efficiency, and maintains tight shut-off against live steam loss.

Constructed with a forged carbon steel body (IS 2004) and stainless steel internals, the BPT 21 / AV 21 operates at pressures up to 21 bar and temperatures up to 285°C.

Key Operational Features & Benefits

• Automatic Air & Gas Evacuation: Operates via an internal stainless steel capsule that stays open when cold to discharge gases, closing tightly once steam arrives.
• Inbuilt Flat Strainer Protection: Fitted with an internal stainless steel flat screen featuring 0.8 mm perforations to block scale and pipe debris.
• Forged Steel Pressure Boundary: Built using IS 2004 forged carbon steel to withstand thermal shocks and pressure surges.
• Cold Hydraulic Safety Margin: Shell tested to a cold hydraulic test pressure of 42 bar to guarantee structural integrity under extreme line conditions.
• Cost-Effective Sourcing: Commercial pricing typically ranges from ₹1,500 to ₹8,000 per unit based on connection style and vendor sourcing on platforms like IndiaMART.

Technical Specifications

Primary Process Applications

• High-Point Air Venting: Installed at high points of steam mains, heat exchangers, and jacketed vessels to eliminate insulating air pockets.
• Instrument & Tracing Lines: Efficient drainage and venting for non-critical steam tracing headers and sterilizer supply lines.
• Autoclave & Kettle Purging: Speeds up batch heating times by rapidly purging non-condensable gases during cold system start-ups.