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Installation
30 CAH-SVX01A-EN
Steam Coil Piping
M-Series air handlers fitted with
steam coils have labeled holes for
piping penetrations. Figure 28 and
Figure 29 illustrate typical steam coil
piping configurations. See Table 2
for the codes of system components
in these figures.
The coil condensate return line must
be piped full size of the condensate
trap connection, except for a short
nipple screwed directly into the coil
header’s condensate return tapping.
Do not bush or reduce the coil return
tapping size.
Table 2. Code of system components
for piping figures
Code System component
FT Float and thermostatic steam trap
GV Gate valve
OV Automatic two-position (ON-OFF)
control valve
VB Vacuum breaker
ST Strainer
AV Automatic or manual air vent
MV Modulating control valve
• Install a 1/2-inch NPT, 15 degree
swing check valve vacuum
breaker with cracking pressure of
0.25 inches Hg (3.5 inches water)
or lower at the top of the coil.
This vacuum breaker should be
installed as close to the coil as
possible.
• For coil types A, AA, N, NS, and
NN, install the vacuum breaker in
the unused condensate return
tapping at the top of the coil.
• Types T and ST coils require that
the vacuum breaker be located
as near as possible to the supply
connection.
• Vent the vacuum breaker line to
atmosphere or connect it into the
return main at the discharge side
of the steam trap
Note: Vacuum breaker relief is
mandatory when the coil is
controlled by a modulating steam
supply or automatic two position
(ON-OFF) steam supply valve.
Vacuum breaker relief is also
recommended when face-and-
bypass control is used.
CAUTION
Coil Damage!
In all steam coil installations, the
condensate return connections must
be at the low point of the coil.
Failure to properly install the
condensate return connection may
result in coil damage from water
hammer, unequal thermal stress,
freeze-up and/or corrosion.
Note: The 1/2-inch NPT, 15 degree
swing check valve vacuum breaker is
recommended because other
vacuum breakers, such as spring-
loaded ball-check breakers, have
cracking pressures as high as 1.25
inches Hg (17 inches of water).
Vacuum breakers with fitting sizes
smaller than 1/2 inch NPT are too
small to relieve vacuum quick
enough to ensure complete
condensate drainage. Other types of
swing check valve vacuum breakers
are acceptable if the fittings size is
not smaller than 1/2-inch NPT and
the cracking pressure is not larger
than 0.25 inches HG (3.5 inches of
water).