National Oilheat Research Alliance 23
Off cycle
Figure 6
• at the end of the cycle the burner shuts off.
• with no steam being supplied, the steam in
the system condenses and creates a vacuum.
• the vents let air back into the system.
• the water level in the return is the same as
in the boiler because there is no pressure difference
in the piping.
Figure 6-Off cycle
Heat Emitter operation with a
typical one pipe system
Startup - Steam approaches the heat emitter
and pushes air out through the vent. Figure 7.
Steam reaches heat emitter - Steam pushes
into the heat emitter and rises to the top, air
continues to be pushed out through the vent.
Heat emitter starts to warm up as condensate
forms and flows back through supply valve.
Figure 8.
Steady state - Vent closes when steam reaches
it, heat emitter releases heat to room and condensate
flow increases. Figure 9.
Figure 7
Figure 8
Figure 9