APPENDIX
JUDGING FLAMES
It is difficult to describe what a flame should look like. In general natural gas pilot and premix burner flames should be adjusted to produce a sharp, forceful, needle-like flame with a well-defined light blue inner cone in a deep blue outer cone. (See photos inside front cover.) Lean flames are pale blue or violet. Rich flames are longer, bushy, yellow- tipped, maybe green-tinged, less noisy. Either rich or lean flames may result in a pilot without enough length or drive to light the main burner or satisfy the flame monitoring system. Observation ports should be installed to allow a side profile view of the flames. The observation ports built into burners rarely give an adequate viewing angle for adjusting flames. If a flame is viewed against a bright radiating background, it is very difficult to observe the flame satisfactorily. CHOICE OF FLAME JUDGING METHODS Metering orifices at every burner = preferred method. See "Field Setup" on page 4 of North American Bulletin 8697 and Supplement 8697-5. Flue gas analysis is an easy way to adjust flames if there is only one zone, or preferably only one burner, and if the chamber has no leaks, no shutters, and no other air entries that cannot be metered. See Handbook Supplement 149. Visual judging of flames for adjusting is not accurate, but must suffice for pilots and small open burners.
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