172-65400MA-01 (BD2) 21 Apr 2010
5
Operation
Principle of Air and Condensate Discharge
1. Start-up: Discharge of Initial Air and Cold Condensate
At start-up, the bimetal air vent ring is cold and has therefore contracted, causing it to
ride up to the narrower area under the disc, thus lifting the disc off the seat and
holding the valve open. This allows for the rapid discharge of initial air and cold
condensate.
2. Steam Enters, Valve Closes
As the bimetal air vent ring is heated by the entering steam, it expands and slips
back down, freeing the disc. The rapid flow of steam creates a low-pressure area
under the disc. The pressure chamber above the disc retains its higher initial
pressure. This difference in the pressures above and below the disc pushes the disc
down against the valve seat, giving the closed valve a tight seal.
3. Condensate Discharge
When condensate enters the trap, the temperature in the pressure chamber drops
due to radiant heat loss, causing the steam to condense and the pressure to drop.
The inlet pressure then pushes up the disc, opening the valve and allowing
condensate to discharge. The bimetal air vent ring remains in its expanded, low
position state. When steam again enters the trap, the valve closes, as in step 2.
Cold
Condensat
Air
Pressure
Chamber
Steam
Condensate
Disc
Air Vent Ring
