Service manual

SERVICING
47
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.
BECKETT BURNER
WARNING
Disconnect Gas and Electrical Power Supply:
In checking main burners, look for signs of rust, oversized
and undersized carry-over ports restricted with foreign ma-
terial, etc .
S-306 CHECKING ORIFICES
A predetermined fixed gas orifice is used in all of these
furnaces. That is an orifice which has a fixed bore and
position.
A
GAS
STREAM
B
DENT OR
BURR
GAS
STREAM
B
The length of Dimension "A" determines the angle of Gas
Stream Defraction,"B".
A dent or burr will cause severe deflection of gas stream.
No resizing should be attempted until all factors are taken
into consideration such as inlet manifold gas pressure, align-
ment, and positioning, specific gravity and BTU content of
the gas being consumed.
The only time resizing is required is when a reduction in
firing rate is required for an increase in altitude.
Orifices should be treated with care in order to prevent dam-
age. 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
Disconnect Gas and Electrical Power Supply:
1. Check orifice visually for distortion and/or burrs.
2. Check orifice size with orifice sizing drills.
3. If resizing is required, a new orifice of the same physi-
cal size and angle with proper drill size opening should
be installed.
S-307 CHECKING GAS PRESSURE
Gas inlet and manifold pressures should be checked and
adjusted in accordance to the type of fuel being consumed.
WARNING
Disconnect Gas and Electrical Power Supply:
1. Connect a water manometer or adequate gauge up-
stream of the gas valve. (If no provisions are provided,
we suggest removing cap from dripleg and install a pre-
drilled cap with hose fitting as shown below.)
Gas Line
Gas Shutoff Valve
Gas Line
To Furnace
Drip Leg Cap
With Fitting
Manometer Hose
Manometer
Open To
Atmospere
MEASURING INLET GAS PRESSURE
2. Remove the pressure tap fitting at the manifold if pro-
vided or from the gas valve and install fitting to connect
another manometer or gauge.