22
STEAM COIL PIPING
Recommendations for Steam Coils — See Fig. 21 and 22.
1. Be sure to provide adequate support for the piping and
design the lines for expansion and vibration.
2. Do not reduce the pipe size on the coil return connection.
Keep the same size through the dirt loop and make any
reduction in the branch to the trap.
3. A vacuum breaker is recommended to prevent conden-
sate from being held up in the coil. Generally the vacuum
break is connected between the coil inlet and the return
main. If the system has a flooded return main the vacuum
breaker should be open to atmosphere and the trap design
should allow for venting large quantities of air.
4. Do not let steam flow drip through the coil and do not at-
tempt to have condensate lift when using a two-position
or modulating valve.
5. Size traps in accordance with the manufacturer’s recom-
mendations. Be sure that the required pressure differential
is available. Do not undersize traps.
6. Float and thermostatic or bucket traps are recommended
for low pressure steam. On high pressure use bucket
traps. Thermostatic traps should only be used for air vent-
ing. Bucket traps are recommended for use with ON/OFF
control.
7. Locate the trap at least 12 in. below the coil return.
8. If a modulating control valve is used be sure to size the
valve properly and do not oversize.
STEAM COIL CONTROLS — Several methods of control
are possible depending on the heating medium to be used, loca-
tion and type of thermostatic control and whether or not modu-
lating or ON/OFF type control is used. Figure 23 shows a typi-
cal control scheme for ON/OFF steam coil in 50XCW units.
Install heating thermostat or connect to the heating side of
an available heating/cooling thermostat so that the unit operates
the fan in the desired operation, either continuous or cycling
with the steam coil. The thermostat should provide the required
connection to activate the fan and the cooling and heating
should not be able to be activated simultaneously.
The freeze stat and the heating relay (HR1) are field-
supplied and installed. Refer to Fig. 18 for typical thermostat
wiring.
½"
Fig. 21 — Typical Steam Distributing Coil Piping
for Open Gravity Systems with
Steam Pressure Below 10 psig
a38-201tf
½
a38-202tf
Fig. 22 — Typical Steam Distributing Coil Piping
for Vacuum-Return Systems with
Steam Pressure Below 10 psig