The Steam Boiler in its simplest form was simply a closed vessel partly
filled with water and which was heated by a fire box, but as steam
plants are divided into two principal parts, the engine and the boiler,
so the latter is divided again into the furnace and boiler, each of
which is essential to the other. The furnace contains the fuel to be
burnt, the boiler contains the water to be evaporated.
There must be a steam space to hold the steam when generated; heating
surface to transmit the heat from the burning fuel to the water; a
chimney or other apparatus to cause a draught to the furnace and
to carry away the products of combustion; and various fittings for
supplying the boiler with water, for carrying away the steam when
formed to the engine in which it is used; for allowing steam to escape
into the open air when it forms faster than it can be used; for
ascertaining the quantity of water in the boiler, for ascertaining the
pressure of the steam, etc., all of which, together with the engine and
its appliances is called A STEAM PLANT.
The forms in which steam generators are built are numerous, but may
be divided into three classes, viz: stationary, locomotive and marine
boilers, which terms designate the uses for which they are intended;
in this work we have to deal mainly with the first-named, although a
description with illustration is given of each type or form.