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m. Adjust the high fire input to match the maximum input
listed on the rating label. At high fire, the gas butterfly
valve should be at least 75 degrees open (more if avail-
able gas pressure is low), and the gas pressure regulator
adjusted to obtain the rating. The input should be
measured using the following equation:
Calculating Natural Gas Input
Gas MBH =
HHV x [(Patm + Pgas)/29.92] x [520/(Tgas +460)] x
[measured ft3/sec] x [3600 sec/hr]
Where:
MBH = 1000's of BTU/M input
HHV = Higher heating value of gas, BTU/cubic feet
Patm = Atmospheric pressure in inches Hg
Pgas = Gas pressure before gas meter in inches Hg
(inches HG = PSIG x 2.04)
Tgas = Gas temperature at the flow meter, in
degrees F
3
Measured ft
= volume of gas measured by meter
sec = Time for measured ft
Note: Some gas meters require a 6 inch wc correction
to Pgas. Consult your meter calibration data.
NOTE: The listed manifold pressure is only an
approximate value and can vary with operating
conditions and normal tolerances. The fuel flow rate
must be measured to obtain an accurate input value.
n. Adjust the air damper to obtain the correct O
o. Modulate the burner to low fire, adjusting the O
as the burner modulates.
p. Adjust the low fire input, using the fuel cam and air
damper adjustments. The linkage may need to be read-
justed to obtain the correct relationship between the fuel
valve and air damper. (Figure I-1)
q. Re-adjust the midfire points for the correct O
r. Adjust the low gas pressure switch to be 10% below
the lowest expected gas pressure.
• With a gauge or manometer at the same location as
the low gas pressure switch, modulate the burner to de-
termine the firing rate with the lowest gas pressure.
• At the lowest gas pressure, adjust the low gas pres-
sure setting up until the switch breaks and causes the
burner to shutdown.
• From the scale reading of the switch, adjust the setting
to a pressure that is 10% lower than the shutdown pres-
sure. For example, if the switch opened at 10 inches as
indicated on the low gas pressure switch, the switch
should be adjusted to a reading of 9 inches.
• Remove the gauge or manometer and plug the
opening.
• Cycle the burner on and off to determine if the limit
works properly.
• If the limit causes nuisance shutdowns because
of small pressure drops during startup, reduce the
pressure setting an additional 5%.
SG Manual
3
to flow through meter
level.
2
level
2
level.
2
s. Adjust the high gas pressure switch to be 10% above
the highest expected gas pressure.
• With a gauge or manometer at the same location as the
high gas pressure switch, modulate the burner to deter-
mine the firing rate with the highest gas pressure.
• At the highest gas pressure, adjust the high gas pres-
sure setting down until the switch opens and causes the
burner to shutdown.
• From the scale reading of the switch, adjust the set-
ting to a pressure that is 10% higher than the shutdown
pressure. For example, if the switch opened at 10 inches
as indicated on the high gas pressure switch, the switch
should be adjusted to a reading of 11 inches.
• Remove the gauge or manometer and plug the opening.
• Cycle the burner on and off to determine if the limit
works properly.
• If the limit causes nuisance shutdowns because of small
pressure drops during startup, reduce the pressure set-
ting an additional 5%.
t. The burner should be operating at low fire to adjust
the air proving switch. Turn the adjusting screw cw (in)
until the burner trips out (shutdown caused by the air flow
switch). Turn the adjustment screw ccw (out)
• From the scale reading of the switch, adjust the set-
ting to a pressure that is 10% higher than the shutdown
pressure. For example, if the switch opened at 10 inches
as indicated on the high gas pressure switch, the switch
should be adjusted to a reading of 11 inches.
• Remove the gauge or manometer and plug the opening.
• Cycle the burner on and off to determine if the limit
works properly.
• If the limit causes nuisance shutdowns because of small
pressure changes during startup, increase the pressure
setting an additional 5%.
u. The burner should be operating at low fire to adjust
the air proving switch. Turn the adjusting screw cw (in)
until the burner trips out (shutdown caused by the air flow
switch). Turn the adjustment screw ccw (out) 1-1/2 turns
from the point of shutdown. Check the operation at higher
rates.
Figure I-3: O
% Rate
30
40
50
100
Page 14
levels
2
Natural Gas
Min %
Max
O2
%O2
5.0
7.0
4.0
7.0
3.0
5.0
3.0
5.0
Startup and Operating Adjustments
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