National Oilheat Research Alliance 33
water has been “steamed
off” and the condensate
has not yet returned.
• all branches receive
steam at about the same
time.
• condensate begins to
form and accumulates in
the steam main drip leg.
• the thermostatic element
of the F&T trap closes
when heated by steam.
• air is slowly exhausted
through the individual
heat emitter’s thermostatic
traps. Figure 3.
Steam pushes into the heat
emitters, Figure 4, following
page.
• the water level in the
boiler continues to drop
slightly
• heat emitters begin to
heat up and cool the
steam.
• condensate in the steam
main drip leg builds up
• air keeps moving from
the heat emitters, through
the traps, to the return.
Figure 2- Thermostat
calls for heat
Figure 3- F&T trap exhausts air