ECONOMICAL USE OP FUEL IN" CREAMERIES. 
17 
where leakage of air through the walls may occur and to give as 
smooth a surface inside as possible so as to lessen the resistance to 
the flow of escaping gases. 
The area of the chimney should be approximately 20 per cent 
greater than the combined flue area of the boiler or boilers which it 
is to serve. Table 3 gives the size of chimney for steam boilers. 
Table 3. — Size of chimney for steam hollers. 
[Calculated from Kent's formula assuming 5 pounds of coal per horsepower-hour.] 
Area 
(square 
feet). 
Diam- 
eter 
(inches.) 
1.23 
1.77 
2.41 
3.14 
4. 91 
5.94 
15 
18 
21 
24 
27 
30 
33 
36 
39 
42 
48 
54 
60 
7.07 
8.30 
9.62 
12.57 
15.90 
19.64 
Height in feet. 
30 40 50 60 70 SO 90 100 110 125 150 175 200 
Commercial horsepower. 
14 
25 
38 
54 
72 
92 
115 
141 
16 
27 
41 
58 
78 
100 
125 
152 
183 
216 
29 
44 
62 
83 
107 
133 
163 
196 
231 
311 
66 
88 
113 
141 
173 
208 
245 
330 
427 
536 
119 
149 
182 
219 
258 
348 
449 
565 
156 
191 
229 
271 
3b5 
472 
593 
204 
2+5 
289 
389 
503 
632 
2b8 
3i6 
426 
551 
692 
342 
460 
595 
636 
800 
Equiv- 
alent 
square 
chim- 
ney- 
side of 
square. 
For pounds of coal burned per hour for any given size of chimney, multiply the figures in the table by 5. 
DAMPERS. 
Each boiler should be provided with a damper in the uptake or 
breeching which should have an effective opening of at least 25 per 
cent greater area than that of the combined area of the tubes. It 
should be arranged for convenient manipulation by the fireman; 
otherwise there will be a tendency to neglect its use. The control 
of the draft should be done through the manipulation of this damper 
rather than by the ash-pit doors. 
BRIDGE WALL. 
The wall just back of the grates is known as the bridge wall and 
extends across the entire width of the furnace to a height somewhat 
above the level of the bars. It has for its object the directing of the 
hot furnace flames and gases, forcing them to rise toward the shell 
of the boiler, and also to hold the fuel at the rear of the grates. The 
distance between the top of the bridge wall and the boiler shell de- 
pends on the kind of fuel used. With anthracite, or hard coal, the 
distance should be less than if soft coal or wood is used. As the 
bridge wall above the grate bars is in the direct path of the flames 
and hence is subjected to a very high temperature, it should be faced 
with fire brick, as ordinary brick soon fuses or crumbles. 
82693°— 19- 
