Form I-ADF, P/N 131805 R6, Page 11
FIGURE 7 - Pressure
Tap Locations for
Measuring Manifold and
Pilot Pressure
Gas Pressure Switches
Gas pressure switches included in the gas train monitor gas pressure downstream from
the safety valves. If the gas pressure at this point on a system equipped with a high gas
pressure switch (standard with Manifolds BM 78 and 79 or optional (BP2 or BP4) with
other manifolds) exceeds the setpoint, the switch will open the electrical circuit to the
burner, stopping all gas ow. The high gas pressure switch is a manual reset device.
An optional low gas pressure switch (Option BP3 or BP4) will shutoff the gas ow if the
gas pressure drops below the setpoint of the low pressure switch. The low gas pressure
switch will automatically reset when the gas pressure rises above the setpoint.
Pilot Supply Pressure
These systems are designed to operate on a natural gas pilot supply pressure of 3.5"
w.c. or a propane gas pilot supply pressure of 6" w.c.
Measure both operating pressure and pilot supply pressure with the blowers in
operation.
Manifold Pressure
Manifold pressure is dened as the gas pressure as measured at the burner pressure
tap. Measure manifold gas pressure with the blowers operating. Minimum gas pressure
at the burner is typically 4.3" w.c. for natural gas or typically 1.5" w.c. for propane.
6.2 Unit Inlet Air
FIGURE 8A - Dimensions
of Outside Air Hood
Option AS2
Outside air hood is shipped
separately for eld installation.
Dimensions are the same for
all sizes.
Provide 14" (356mm)
clearance from the bottom of
the air hood to the mounting
surface.
6.2.1 Screened Outside Air Hood without Filters (Option AS2)
Option AS2, Screened Outside Air Hood, is a weatherized hood designed to be
eld-assembled and installed around the inlet air opening. The air hood includes a
pre-assembled louver assembly designed to help eliminate moisture from the inlet air.
Complete instructions are packaged with the air hood option.
CAUTION: It is recommended that the inlet to the outside air hood
not be facing into the prevailing wind.
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