Modern Types of Boilers

MODERN TYPES OF BOILERS Although such boilers as the Haystack, Wagon, and others were fairly satisfactory in the period in which they were invented, they could not stand the higher pressures that soon became common.

About the beginning of the nineteenth century the cylindrical boiler was introduced. The earliest forms were the plain cylindrical boiler and the " Egg-end " boiler. The difference was in the form of the ends -- those of the former were flat and of cast iron, while the ends of the latter were hemispherical and made of wrought iron. The egg-end boiler required no staving or bracing because its form is, with the exception of a sphere, the strongest to resist internal pressure.

The Cylindrical Boiler

consisted of a shell of wrought-iron boiler plate and ends of the same material or of cast iron. It was set in brickwork as shown in Fig. 3. The boiler was about twothirds filled with water, the remaining forming the steam space. To collect and store the steam as it rose from the water a steam dome was added. The steam pipe was attached to the dome to which the safety valve also was connected. The hot gases from the fire passed under the boiler to the rear and then to the chimney.

The heating surface of this type is small with a given diameter unless the boiler is made very long. As all sediment collects in the bottom, where the heat is most intense, the plates are liable to burn. Since sediment and scale are poor conductors of heat, the heat remains in the plates and overheats them instead of flowing to the water.

The disadvantages (the small heating surface and the collection of sediment) do not seem so serious when one considers the simplicity of construction, strength, durability, and ease of repairing and cleaning.

The.plain cylindrical boiler was adapted for mining districts, iron works and other places where fuel is abundant and skilled boiler makers are not readily found. This boiler was made very long to get the required heating surface, the length sometimes exceeding fifty feet.