Figure 4-Steam pushes
into heat emitters
• condensate begins to
form in the heat emitters
and flows through the
thermostatic traps to the
return
• the water level in the
condensate tank begins
to rise.
• the float valve of the
F&T trap cycles as condensate
raises the float.
Steady state heating
• the boiler water level
continues to drop
because of the conden
sate out in the system.
• steam fills the heat
emitters
• the heat emitter’s
thermostatic traps close
when exposed to steam
34 National Oilheat Research Alliance
temperature and cycle
on and off throughout
the heating cycle.
• the condensate return
system cycles based on
water level in the tank.
• the boiler continues
to fire until the thermostat
is satisfied or
the limit control setting
is reached. Figure 5
Off cycle
• at the end of the cycle the
thermostat shuts the burner off.
• the steam in the system
condenses and creates a
vacuum.
• the condensate tank vent
lets air back into the system
and breaks the vacuum.
Figure 5-Steady state