Adjustment Procedures
5-16
750-96 (revised 2010)
Model CB Packaged Boiler Manual
FIGURE 5-6. Butterfly Gas Valve
When proper gas flow is obtained, take a flue gas analysis reading the CO
2
should be between 9-1/2% and
10-1/2% and the corresponding O
2
reading should be 2% to 4%.
With the high fire air-fuel ratio established, the gas pressure regulator needs no further adjusting.
After making certain that the air control damper and its linkage are correctly adjusted to provide the proper
amount of secondary air and after adjusting the gas pressure regulator, final adjustment can be made, if neces-
sary, to the gas modulating cam to obtain a constant air-fuel ratio throughout 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 gas fuel at that setting. This adjustment is made to the metering cam by
means of adjusting screws which are turned out (counterclockwise from the hex-socket end) to increase the flow
of fuel, and in (clockwise from the hex-socket end) to decrease it. Flow rate is highest when the cam follower
assembly is closest to the jackshaft.
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