28 National Oilheat Research Alliance
Figure 6
One pipe parallel downfeed pumped return
system (Figure 6)
• In addition to the components added to
convert an upfeed gravity return system to
a pumped return, downfeed systems
require additional F&T traps at the end of
each riser.
• Without these additional traps, there is a
risk of water hammer and reverse steam
flow due to the downfeed risers being con-
nected together above the boiler’s water
line.
• These traps must be located at least 15" be-
low the lowest steam carrying pipe
connected to them to allow room for the
condensate to build up enough to push
through the trap on start up.
• The main vent is optional (but recommend-
ed) on these systems because F&T traps
allow air to escape.
One Pipe Parallel