Check the Manifold Pressure
A tapped opening is provided in the gas valve to facilitate
measurement of the manifold pressure. See the “Outlet
Pressure Tap” in Figures 36, 37, 38, & 39. A “U Tube”
manometer having a scale range from 0 to 12 inches of
water should be used for this measurement. The mani-
fold pressure must be measured with the burners oper-
ating .
To adjust the pressure regulator, remove the adjustment
screw or cover on the gas valve. Turn out (counter-
clockwise) to decrease pressure, turn in (clockwise) to
increase pressure. Only small variations in gas flow
should be made by means of the pressure regulator
adjustment. For natural gas, the manifold pressure must
be between 3.2 and 3.8 inches water column (3.5 nom-
inal). For propane gas, the manifold pressure must be
between 9.7 and 10.3 inches water column (10.0 nomi-
nal). Any major changes in flow should be made by
changing the size of the burner orifice.
Check Gas Input (Natural Gas Only)
To measure the gas input using the gas meter proceed as
follows:
1. Turn off gas supply to all other appliances except the
furnace.
2. With the furnace operating, time the smallest dial on
the meter for one complete revolution. If this is a 2
cubic foot dial, divide the seconds by 2; if it is a 1 cubic
foot dial, use the seconds as is. This gives the
seconds per cubic foot of gas being delivered to the
furnace.
3. INPUT = GAS HTG VALUE x 3600 SEC. PER CUBIC
FOOT (3600 is a conversion factor- 3600 seconds =
1 hour.)
Example: Natural gas with a heating value of 1000
BTU per cubic foot and 34 seconds per cubic foot as
determined by Step 2, then:
Input = 1000 x 3600 x 34
= 106,000 BTU per Hour
NOTE: BTU content of the gas can be obtained from
the gas supplier.
This measured input must not be greater than the
input indicated in Specification Sheet.
4. Relight all other appliances turned off in Step 1
above. Be sure all pilot burners are operating.
Check Burner Flames
Flames should be stable, soft and blue, (dust may cause
orange tips but they must not be yellow), extending
directly outward from the burners without curling, floating
or lifting off.
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