It may be useful to add the following data relating to this approved steam generator, being the principal dimensions and other data of the boiler shown in [fig. 18]:
| Steam pressure, 75 lbs. per sq. inch. | ||
| Length, 27 feet. | ||
| Diameter, 7 feet. | ||
| Weight, total, 151⁄2 tons. | ||
| Shell plates, 7⁄16 inch. | ||
| Furnace diameter, 33 inches. | ||
| Furnace Plates, 3⁄8 inch. | ||
| End plates, 1⁄2 inch. | ||
| Grate area, 33 sq. feet. | ||
| Heating surface: | ||
| In furnace and flues | 450 | sq. feet. |
| In Galloway pipes, | 30 | „ |
| In external flues, | 370 | „ |
| 850 | sq. feet. | |
We have thus detailed step by step the improvement of the steam boiler to a point where it is necessary to describe at length the locomotive, the marine, the horizontal tubular and the water tube boilers, which four forms comprehend ninety-nine out of one hundred steam generators in use in the civilized world at the present time.
MARINE BOILERS.
The boilers used on board steamships are of two principal types. The older sort used for steam of comparatively low temperature, viz.: up to 35 lbs. per square inch, is usually made of flat plates stayed together, after the manner of the exterior and interior fire boxes of a locomotive boiler.
Medium high pressure marine boilers, constructed for steam of 60 to 150 lbs. per square inch, are circular or oval in cross section, and are fitted with round interior furnaces and flues like land boilers. There are many variations of marine boilers, adapted to suit special circumstances. [Fig. 22] shows a front elevation and partial sections of a pair of such boilers and [Fig. 23 ]shows one of them in longitudinal vertical section.
THE MARINE STEAM BOILER
Fig. 22.