Adjustment Procedures
6-18
750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
Another product of combustion is CO (carbon monoxide) and is shown in both percentage and parts per million
(ppm). The maximum CO level standardly allowed is less than 400 ppm. However, this may change subject to local
regulations.
The percent O
2
recorded on an instrument equates to percent excess air, i.e., 3% O
2
is approximately 15% excess
air and 4% O
2
is approximately 20% excess air. The exact percentage of excess air is a mathematical calculation
based on an ultimate fuel analysis of the fuel being fired.
It is generally recommended that O
2
readings of between 3% and 4% be attained with less than 400 ppm CO, at
high-fire.
Using information from section 6.16, determine the standard conditions of gas pressure and flow for the boiler
size and attached gas train. Calculate the actual pressure and flow through the use of correction factors that com-
pensate for incoming gas pressure and altitude.
Basically, gas adjustments are made with a gas pressure regulator, which controls the pressure and with the butterfly
gas valve which directly controls the rate of flow.
FIGURE 6-12. Butterfly Gas Valve
In initially setting the linkage:
1. Back off the low fire stop screw on the butterfly valve so that the valve is closed.
2. Then run the screw out to touch the arm, and give it two complete turns.
3. Adjust the connecting rod so that the override tension is released and so that the arm is now just touching the
stop screw.
4. Tighten the locknuts on all ball joints.
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