750-96 (revised 2010)
Model CB Packaged Boiler Manual
5-19
5.12 — Fuel Oil Combustion Adjustment
Efficient combustion cannot be solely judged by flame condition or color, although they may be used in making
approximate settings. This should be done so that there is a bright sharp flame with no visible haze.
Proper setting of the air-fuel ratios, at all rates of firing must be established by the use of a combustion gas ana-
lyzer. This instrument measures the content, by percentage, of carbon dioxide (CO
2
), oxygen (O
2
), and carbon
monoxide (CO) in the flue gas.
Burner efficiency is measured by the amount of percent of CO
2
present in the flue gas. The ideal setting from a
standpoint of efficiency is reached when the percentage of oxygen in the flue gas is zero. It is, however, more
practical to set the burner to operate with a reasonable amount of excess air to compensate for minor variations
in the pressure, temperature, or burning properties of oil. 15% to 20% excess air is considered reasonable and
this should result in an approximate CO
2
reading of 12-1/2% to 13%.
The burner should never be operated with an air-fuel ratio that indicates a detectable percentage of carbon monox-
ide.
Through the use of the manual flame control slowly bring the unit to high fire by stages. At the high fire position the
air damper should be fully opened and the air and oil pressure readings should be on the order of those given in
Chapter 4.
Take a flue gas analysis reading at this point. If necessary, make adjustments to the fuel oil controller to increase
or decrease oil pressure. This should be done before making any effort to adjust the screws in the metering cam.
Ideally, the cam profile spring should be as close to the cam casting as practical and it is more desirable to lower
the oil pressure to reduce flow, if necessary, than to extend adjusting screws to an extreme position in an effort to
cut back on flow.
After making certain that the air control damper and its linkage are operating properly to provide the proper
amount of secondary air and that fuel oil pressure settings are correct, final adjustment can be made, if neces-
sary, to the oil modulating cam to obtain a constant fuel-air ratio through the entire firing range.
Since the input of combustion air is ordinarily fixed at any given point in the modulating cycle, the flue gas reading
is determined by varying the input of fuel at that setting. This adjustment is made to the metering cam by means
of adjusting screws, which are turned out (counterclockwise from hex-socket end) to increase the flow of fuel and
in (clockwise from hex-socket end) to decrease it. Flow rate is highest when the cam follower assembly is closest
to the jackshaft.
If oil pressure, primary air pressure, and linkages are properly adjusted, the metering cam should require minimal
adjustment.
If adjustment is necessary, follow this recommended procedure:
1. Through the flame control switch, position the cam so that the adjusting screw adjacent to the end or high fire
screw contacts the cam follower. Make a combustion analysis at this point.
2. If an adjustment is necessary, turn the adjustment screw accordingly to increase or decrease fuel flow. Take a
combustion reading to verify input.
3. Repeat as necessary until the desired flow is obtained.
NOTE: Do not use any lubricant on the adjusting setscrews. These have a nylon locking insert intended to provide lock-
ing torque and resistance to loosening.
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