Page 330 - Boiler_Operators_Handbook,_Second_Edition

Plants and Equipment 315

the heating season and clean it if necessary. I’ve seen the distribution header (B) drawing primary air along
them with large pieces of scale from the heat exchanger with it through the opening that’s adjusted by the sleeve
laying on top of the runners and, on one occasion, re- (E). The mixture then flows into the flame runners (A)
moved the runners and held them up to drain about a and out the ports where heat from a spark or adjacent
cup of rust from the inside of each tube! fire provides ignition energy to start the combustion.
If your home has one of those gas furnaces you also Always remember that additional air, secondary air, is
want to check the furnace sections for cracks and open required to complete the combustion and enters through
seams. If there’s a way for the products of combustion openings like the one at (F).
to get into the heated air side of the furnace it will most The primary air—gas mixture is adjusted to pro-
likely contain considerable quantities of poisonous car- duce a stable flame over the head or flame runners by
bon monoxide. The price of a furnace isn’t worth the risk adjusting the sleeve or shutter. Either one has a locking
of dying so you should replace any rusty, mis-shaped or screw to ensure the piece stays where it was adjusted.
cracked furnace. The flame should burn clean and stable just above the
On atmospheric burners primary air adjustment distribution ports. Lighting these burners can be inter-
is accomplished by moving a sleeve (Figure 10-48) or esting at times, especially during initial startup, because
rotating a shutter (Figure 10-49) thereby changing the the pilot only lights one to four ports on the burner head
opening for primary air. The gas nozzle (D in Figure or runner and the rest of the burner is ignited by flame
10-48) converts much of the static pressure in the gas at the adjacent port.
to velocity pressure. The high velocity gas shoots into Some atmospheric burners provide a degree of
modulation and turndown by cutting out some of the
jets or controlling groups of jets with individual shutoff
valves and may be augmented by matching combustion

Figure 10-46. Gas burner head

Figure 10-48. Primary air sleeve

Figure 10-47. Flame runners Figure 10-49. Primary air shutter