Coil Piping and Connections
40 CLCH-SVX009J-EN
To prevent coil damage, complete the following
recommendations:
• Install a 1/2-in. NPT, 15 degree swing check valve
vacuum breaker with cracking pressure of 0.25 inches
Hg (3.4 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 type NS, install the vacuum breaker in the
unused condensate return tapping at the top of the
coil.
• 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.
Proper steam trap installation is necessary for satisfactory
coil performance and service life. For steam trap
installation:
1. Install the steam trap discharge 12 inches below the
condensate return connection. Twelve inches provides
sufficient hydrostatic head pressure to overcome trap
losses and ensures complete condensate removal.
a. Use float and thermostatic traps with atmospheric
pressure gravity condensate return, with automatic
controls, or where the possibility of low-pressure
supply steam exists. (Float and thermostatic traps
are recommended because of gravity drain and
continuous discharge operation.)
b. Use bucket traps only when the supply steam is not
modulated and is 25 psig or higher.
Note: Trane steam coils require a minimum of 2 psi of
pressure to assure even heat distribution.
2. Trap each coil separately to prevent holding up
condensate in one or more of the coils.
3. Install strainers as close as possible to the inlet side of
the trap.
4. If installing coils in series airflow, control each coil
bank independently with an automatic steam-control
valve. Size the traps for each coil using the capacity of
the first coil in direction of airflow.
5. Use a modulating valve that has linear flow
characteristics to obtain gradual modulation of the coil
steam supply.
Note: Do not modulate systems with overhead or
pressurized returns unless the condensate is
drained by gravity into a receiver, vented to
atmosphere, and returned to the condensate
pump.
6. Pitch all supply and return steam piping down 1 in. for
every 10 feet in the direction of the steam or
condensate flow.
Note: Do not drain the steam mains or take-offs through
the coils. Drain the mains ahead of the coils
through a steam trap to the return line.
7. Ensure overhead returns have 1 psig of pressure at the
steam trap discharge for every 2 feet of elevation for
continuous condensate removal.
NOTICE
Breaker Cracking Pressure!
Failure to follow these instructions could result in
equipment damage. The 1/2-in. 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 in. 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-in. NPT and the cracking pressure
is not larger than 0.25 inches HG (3.5 inches of water).
NOTICE
Coil Condensate!
Failure to follow these instructions could result in
equipment damage. Condensate must flow freely from
the coil at all times to prevent coil damage from water
hammer, unequal thermal stresses, freeze-up and/or
corrosion. In all steam coil installations, the condensate
return connections must be at the low point of the coil.
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