34
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 34 illustrates the typical piping at the end of every steam
supply main. Omitting this causes many field problems and failed
coils.
Figure 35 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 36 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 37 illustrates the basic condensate lift piping.
Following the piping diagrams in Fig. 33-37, make all connections
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 non-condensible
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.
NOTE: All hot water coils have 1-1/2-in. MPT.
Table 10 — Hot Water Coil Circuiting Data
39L UNIT SIZE
03
06
08
10
12
15
18
21
25
No. of Circuits
1-ROW
H
6
8
10
10
10
13
15
15
13
2-ROW
H
F
6
8
10
10
10
13
15
15
13
12
16
20
20
20
26
30
30
36
LEGEND
F
— Full Circuit
H
— Half Circuit