McQuay IM 987
33
Mechanical Installation
Steam Coil Piping (All Units)
The steam heat section consists of two stacked coils pitched at
1/8" (3 mm) per foot (305 mm) as shown in
Figure 35
to
provide positive condensate removal. When no factory piping
or valve is included, the coil connections are 2.5" male NPT
iron pipe.
Note:
The valve actuator spring returns to a stem up position
upon power failure. This allows full flow through the coil.
Figure 35: Steam Heat Section (Shown with Factory Valve
and Piping)
With the factory piping and valve package, the two coil
supplies are piped in parallel and controlled through a single
two-way valve. The field supply connection is of the same
female NPT size as the valve. Field return connections are
made at the 2.50" male NPT fittings on each of the two stacked
coils.
Note:
Refer to the sections on steam coil piping and trap
recommendations for additional information.The valve
actuator spring returns to a stem up position upon power
failure. This allows full flow through the coil.
Figure 36: Two-Way Valve Package
Steam Piping Recommendations
1
Be certain that adequate piping flexibility is provided.
Stresses resulting from expansion of closely coupled
piping and coil arrangement can cause serious damage.
2
Do not reduce pipe size at the coil return connection.
Carry return connection size through the dirt pocket,
making the reduction at the branch leading to the trap.
3
Install vacuum breakers on all applications to prevent
retaining condensate in the coil. Generally, the vacuum
breaker is to be connected between the coil inlet and the
return main. However, if the system has a flooded return
main, the vacuum breaker to the atmosphere; the trap
design should allow venting of the large quantities of air.
4
Do not drain steam mains or takeoffs through coils.
Drain mains ahead of coils through a steam trap to the
return line.
5
Do not attempt to lift condensate when using modulating
or on-off control.
6
Pitch all supply and return steam piping down a
minimum of 1" (25 mm) per 10 feet (3 m) of direction of
flow.
Return
Lower
Coil
2.12 " ODM
Copper Coil
Connections
Upper
Coil
Supply
Return
