Metal Worker Plumber & Steam Fitter - Clpdigital.org

July 16, 1920 METAL WORKER, PLUMBER AND STEAM FITTER 71
In such installations as these, as in all hot-water
heating work, the water will circulate through the system
whenever there is fire in the heater, provided that
/Air Loop
Dra/77 AaAe-
Fig 22. Supply and Return Connections from Same
Main Mitre Coil Below It.
the cooling center is above the heating center, as previously
explained, unless there are air pockets or other
obstructions inside the pipe.
In order to induce a reasonably rapid circulation
where there is much retarding force, care should be
taken to remove every possible impediment that would
tend to retard the circulation. To do this, the pipes
should be a size larger, and the overhead mains often
two sizes larger, than would be necessary if the radiation
were' above the mains. Care should be taken never
to butt return lines, and such details as the careful
reaming of pipes, which ordinarily may be omitted,
should be attended to.
When the system involves the heating of a number
of radiators or wall coils, the flow should rise directly
to the highest point and be vented as already described.
Then the main should run around the building
as in the single circuit system. If there should
happen to be a room or two upstairs which needs to
be heated, these radiators should be connected as already
described, and they will be a great help in accelerating
the circulation through the radiators below.
The returns from the radiators near the heater may
be carried back separately if desired, but care should
be taken that the high places should be vented as before
described.
rffP/pe ^-Ceiling
Wains'
WCTanK
Fig. 24. A System Without an Expansion Tank.
Mitre coils with the perpendicular pipes extending
high on the wall give the best results with this sort
of work. The horizontal header should be the one
nearest the heater as the water flows, and the return
pipe which runs up into the main again should be taken
from the bottom of the return header as shown in
Fig. 22. These pipes should be the full size of the
main. Another pipe of the same size should lead
from the other end of the flow header and up into the
bottom of the main as shown. If the main between
these two points was entirely open, the water would
flow freely through it and would never pass through
the coil at all. If the main, between these two points,
were plugged tight, or a piece of it cut out, it would
be impossible to keep the air from collecting at the
high points and shutting off the circulation.
The scheme of plugging the main, leaving only a
/^\ Fig. 23. The Method That
Insures Circulation and
Heating.
small hole at the top for the passage of air, has been
tried without much success, it being difficult to have a
hole so small that no considerable quantity of water
will go through it and thus throw the plant out of
operation further along, and still be large enough to
keep the main always vented. This may be done by
the use of the air trap around a gate valve, as shown
in Fi"-. 22 and 23. If the room is so high that this
valve would be difficult to reach, a quick opening valve
operated by means of a pulley and chain may be used.
When the system is filled with water, which should
always be done by means of a pipe connected to return
main or into the bottom of the heater, the air
which the water displaces flows freely from the low
to the high part of the main through the air trap.