All About Engines

Raising Steam 71 similar to those of a Lancashire boiler, but shorter, and that the gases return through tubes above the furnaces. A single-ended boiler may have one, two, or three furnaces, according to size, and a double- ended boiler four or six furnaces. Compared with a Lancashire boiler, however, they are short and fat, this form fitting most economically into the space available on board ship. A large specimen is no light weight — each of the twenty-four double-end- ed boilers ontheOZym- pic weighs 105 tons. ~ , Fig. 37.—Some vertical boilers Several types of vertical boiler are shown in Fig. 37, and another one was illustrated in Fig. 1. In all cases the firebox is totally enclosed in the boiler shell to which it is attached by a ring round the lower end, another round the fire door, and stays. In order to increase the heating surface, water cross tubes, or fire tubes, are fitted. These boilers are rarely made in large sizes or for high pressures, and are usually to be found in small factories and work- shops, or supplying steam for winches and cranes.