Adjustment Procedures
6-16
750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
Since the gas flow rate is based on standard conditions of flow, correction must be made for the supply pressure
through the meter of 3 psig. Determine the flow rate by dividing the Btu content of the gas into the burner input
(Figure 6-8) and “correct” this answer by applying the correction factor for 3 psig (Figure 6-9).
Btu/hr input
= CFH (Cubic feet/hour)
Btu/cu. ft.
OR
25,100,000
= 25,100 CFH (at 14.7 lb atmospheric base pressure)
1,000
THEN
25.100
= 21,271 CFH
1.18
This is the CFH (at line pressure) that must pass through the meter so that the equivalent full input requirement of
25,100 CFH (at base pressure) will be delivered.
6.16.4 — Checking Gas Flow
Your gas supplier can generally furnish a gas meter flow chart from which gas flow can be determined. After a
short observation period, the information aids in adjusting the regulator to increase or decrease flow as required to
obtain the rating.
Final adjustment of the gas fuel is carried out be means of the adjusting screws in the gas modulating cam, while
performing a combustion efficiency analysis. See Section 6.17 for details.
6.17 — Gas Fuel Combustion Adjustment
After operating for a sufficient period of time to assure a warm boiler, adjustments should be made to obtain effi-
cient combustion.
Burner efficiency is measured by the amount or percentage of O
2
present in the flue gas. O
2
readings determine the
total amount or excess air in the combustion process, above the point of stoichiometric combustion or perfect
combustion. Stoichiometric combustion is a term used to describe a condition when there is the exact amount,
molecule for molecule, of air for the fuel burned. This can be accomplished under laboratory conditions, however,
NOTE: The information given in this section is for all practical purposes sufficient to set and adjust controls for gas
input. Your gas supplier can, if necessary, furnish exact correction factors that take into consideration Btu content,
exact base pressure, specific gravity, temperature, etc. of the gas used.
NOTE: All adjustment should be done by a qualified boiler operator or your local Cleaver-Brooks service representa-
tive.
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