Boiler, STEAM

Ve el for the generation and storage of steam for industrial purposes. Its design aims at economy in generation of steam from the fuel, and at safety in storage of the steam and heated water. The sphere is the form adapted to resist internal pre ure, but it is not suitable to most economical transfer of heat, nor is it easy to construct on a large scale. The cylinder is next best for resisting pre ure, and is well adapted to absorb heat. The conductivity for heat po e ed by copper has made it in the past a favorite material for boiler purposes. It is now limited to non-American practice for locomotive fire-boxes. (See FIRE-BOX and LOCOMOTIVE.) Wrought iron and steel are most used, cast iron being applicable only to a few sectional types. The usual types are as follows: 1st. The plain cylinder boiler, best suited for impure water and long flame or gaseous fuels. It is the usual blast furnace boiler of this country, and sometimes 60 ft. in length. A modification of this is the French or Elephant or Union IMG:content-0560.png:[graphic] IMG:content-0561.png:[graphic][merged small][merged small] Flue boilers are applicable for inferior waters and bituminous fuels. 3d. The tubular or multi tubular boiler. The few flues of large diameter in the water space are replaced by a great number of smaller tubes, expanded into the two heads. A large increase of heating surface is secured and rapid steaming capacity. Tubular boilers are applicable for pure waters and anthracite or non-flaming fuels. 4th. The locomotive and upright boilers are modifications of the tubular, in which the fire is internal to the water being evaporated, and is in a fire-box. These require no setting, cause little lo by radiation of heat, and are rapid steamers. The upright boilers are likely to give wet steam, and the upper ends of the tubes are not submerged in water, giving rise to leakage and failure at that place. The fire-engine boiler is an upright, but is often made with the tubes submerged. 5th. Sectional boilers, in which the generation and storage are carried on in a number of separate ve els connected to deliver at one outlet. By this means failure or rupture of one unit does not nece itate the renewal of the boiler as a whole, nor will the failure of one section nece arily involve a disaster, as the overpre ure will relieve itself at safe velocity through the small outlet thus afforded. Such boilers are also easily transported. The sections are either spherical or more usually made up of lap-welded wrought-iron tubes, the water being inside. 6th. Water-tube or coil boilers, in which the water circulates inside of the tubes, while the fire is outside. Several of the sectional boilers are of this type. In the coil boilers, however, the coil is a continuous spiral coil, and the water is circulated in it, either naturally or by a pump.