This
"superheating" evaporates the globules and dries the steam, besides raising
its temperature. The small water-tube is preferable to the small fire-tube
connecting furnace and chimney, as its surface is exposed more directly to
the flames; also it increases, instead of decreasing, the total volume of
water in the boiler.
A Vertical Boiler.
[Illustration: FIG. 80.--Details of vertical boiler.]
The vertical boiler illustrated by Fig. 80 is easily made. The absence of a
water jacket to the furnace is partly compensated by fitting six
water-tubes in the bottom. As shown, the barrel is 8 inches long and 6
inches in outside diameter, and the central flue 1-1/2 inches across
outside solid-drawn 1/16-inch tubing, flanged ends, and four 1/4-inch
stays--disposed as indicated in Fig. 80 (a) and (b)--are used. The 5/16 or
3/8 inch water-tubes must be annealed and filled with lead or resin before
being bent round wooden templates. After bending, run the resin or lead out
by heating. The outflow end of each pipe should project half an inch or so
further through the boiler bottom than the inflow end.
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