64
SERVICING
The main burners are used to provide complete combustion
of various fuels in a limited space, and transfer this heat of
the burning process to the heat exchanger.
Proper ignition, combustion, and extinction are primarily due
to burner design, orifice sizing, gas pressure, primary and
secondary air, vent and proper seating of burners.
34.5" Burner
WARNING
D
ISCONNECT
ALL
G
AS AND
E
LECTRICAL
P
OWER
S
UPPLY.
In checking main burners, look for signs of rust, oversized
and undersized carry over ports restricted with foreign mate-
rial, etc, burner cross-over slots should not be altered in
size.
S-306 CHECKING ORIFICES
40,000 - 120,000 BTUH models have factory installed #45
natural gas orifices. The 30,000 BTUH models have #50
orifices. The only time resizing is required is when a reduc-
tion in firing rate is required for an increase in altitude or a
furnace is being converted for use with LP gas. Orifices
should be treated with care in order to prevent damage. They
should be removed and installed with a box-end wrench in
order to prevent distortion. In no instance should an orifice
be peened over and redrilled. This will change the angle or
deflection of the vacuum effect or entraining of primary air,
which will make it difficult to adjust the flame properly. This
same problem can occur if an orifice spud of a different length
is substituted.
WARNING
D
ISCONNECT
ALL
G
AS AND
E
LECTRICAL
P
OWER
S
UPPLY.
1. Check orifice visually for distortion and/or burrs.
2. Check orifice size with orifice sizing drills.
A
GAS
STREAM B
The length of Dimension "A" determines the angle of Gas
Stream "B".
DENT OR
BURR
GAS
STREAM B
A dent or burr will cause a severe deflection of the gas stream.
S-307 CHECKING GAS PRESSURE
GAS SUPPLY PRESSURE MEASUREMENT
G
AS
P
RESSURE
T
EST
The line pressure supplied to the gas valve must be within the
range specified below. The supply pressure can be measured at
the gas valve inlet pressure tap or at a hose fitting installed in the
gas piping drip leg. The supply pressure must be measured
with the burners operating. To measure the gas supply pres-
sure, use the following procedure.
INLET
OUTLET
Gas Valve On/Off
Selector Switch
White-Rodgers Model 36J54 (Two-Stage)
