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STEAM COILS
Position the steam supply connection at the top of the coil, and the
return (condensate) connection at the bottom. The coil tubes must
incline downwards toward the return header connection for con-
densate drainage. See Fig. 98-102.
Figure 98 illustrates the normal piping components and the sug-
gested locations for high, medium, or low-pressure steam coils.
The low-pressure application (zero to 15 psig) can dispense with
the 1/4-in. petcock for continuous venting located above the vacu-
um breaker (check valve).
Note the horizontal location of the 15-degree check valve, and the
orientation of the gate/pivot. This valve is intended to relieve any
vacuum forming in the condensate outlet of a condensing steam
coil, and to seal this port when steam pressure is again supplied to
the coil. It must not be installed in any other position, and should
not be used in the supply line.
For coils used in tempering service, or to preheat outside air, in-
stall an immersion thermostat in the condensate line ahead of the
trap. This will shut down the supply fan and close the outdoor
damper whenever the condensate falls to a predetermined point,
perhaps 120°F.
NOTE: Do NOT use an immersion thermostat to override a duct
thermostat and open the steam supply valve.
For vacuum return systems, the vacuum breaking check valve
would be piped into the condensate line between the trap and the
gate valve instead of open to the atmosphere.
Figure 99 illustrates the typical piping at the end of every steam
supply main. Omitting this causes many field problems and failed
coils.
Figure 100 shows the typical field piping of multiple coils. Use
this only if the coils are the same size and have the same pressure
drop. If this is not the case, an individual trap must be provided for
each coil.
Figure 101 shows a multiple coil arrangement applied to a gravity
return, including the open air relief to the atmosphere, which
DOES NOT replace the vacuum breakers.
Figure 102 illustrates the basic condensate lift piping.
Following the piping diagrams in Fig. 98-102, make all connec-
tions while observing the following precautions:
•
Install a drip line and trap on the pressure side of the inlet
control valve. Connect the drip line to the return line
downstream of the return line trap.
•
To prevent scale or foreign matter from entering the con-
trol valve and coil, install a 3/32-in. mesh strainer in the
steam supply line upstream from the control valve.
•
Provide air vents for the coils to eliminate noncondensable
gases.
•
Select a control valve according to the steam load, not the
coils supply connection size. Do not use an oversized con-
trol valve.
•
Do not use bushings that reduce the size of the header re-
turn connection. The return connection should be the same
size as the return line and reduced only at the downstream
trap.
•
To lift condensate above the coil return line into overhead
steam mains, or pressurized mains, install a pump and re-
ceiver between the condensate trap and the pressurized
main. Do not try to lift condensate with modulating or on-
and-off steam control valves. Use only 15-degree check
valves, as they open with a lower water head. Do not use
45-degree or vertical-lift check valves.
•
Use float and thermostatic traps. Select the trap size ac-
cording to the pressure difference between the steam sup-
ply main and the return main.
•
Load variations can be caused by uneven inlet air distribu-
tion or temperature stratification.
•
Drain condensate out of coils completely at the end of the
heating season to prevent the formation of acid.
Unit
12"
a39-4310
Min.
Dirt Leg (6 in.)
15° Check Valve
* When end of supply main, see Fig. 99.
NOTES:
1. Flange or union is located to facilitate coil removal.
2. Flash trap may be used if pressure differential between steam and con-
densate return exceeds 5 psi.
3. When a bypass with control is required.
4. Dirt leg may be replaced with a strainer. If so, tee on drop can be
replaced by a reducing ell.
5. The petcock is not necessary with a bucket trap or any trap which has
provision for passing air. The great majority of high or medium pressure
returns end in hot wells or deaerators which vent the air.
Fig. 98 — Low, Medium or High Pressure
Steam
Supply
to Unit
Dirt Leg
Globe Valve
(Plug Type)
Drip
Line
Condensate
Return
From Unit
Gate Valve
a39-2362
NOTES:
1. A bypass is necessary around trap and valves when continuous opera-
tion is necessary.
2. Bypass to be the same size as trap orifice but never less than
Fig. 99 — Dripping Steam Supply to
Condensate Return
135
1/4 in. Pet Cock for
Continuous vent
*
15° Check Valve for
Breaking Vacuum
1/2 in. Line
Note 1
Gate Valve
Float or
Bucket Trap
(Note 2)
Condensate
Return Main
Coil Piping
Gate
Valve
Steam Supply Main
Float and Thermostatic
Trap
Gate Valve
Open Air Relief to
Atmosphere Close
to Unit. Required on
Low Pressure Gravity
Return Systems
Condensate
Return Main
Steam Sup
Main
1
/
inch.
2
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