Originally, saturated steam was the only sort employed in steam engines, but as multiple-expansion developed and higher pressures were carried in boilers the use of superheated or dry steam at as high as C. was tried, and it was demonstrated that the hotter the steam was the more it expanded and the greater the power to be got out of it. Superheating began experimentally about 1895 and was operated in connection with an econo mizer. This is a mechanism for utilizing the waste heat and turning it into the feed-water, so that hot water, close to the boiling point, can be supplied to the boiler. Engines using super heated steam have been operated with as little as 1.3 pounds of coal per indicated horse power. See LOCOMOTIVE.
Steam Turbines comprise a class of heat engines in which the kinetic energy of expand ing steam is utilized to drive a wheel and thus convert the natural heat energy of steam di rectly into mechanical energy in the form of rotary motion. The principal forms are the Parsons, De Laval, Seger and Curtis turbines, and their first field of application and develop ment was in the marine service. Noteworthy examples of their application are the Lusiiania and Mauretania ocean steamships and many of the modern ((dreadnaught* type of battle ships. They are now coming into use in large 1:ghting stations and mammoth manufacturing plants. See TURBINE.
Hydraulic Mechanical power is obtained from flowing water by its weight, pressure or impact, utilized in various forms of water wheels, turbines, hydraulic rams and water-pressure engines. In the water-pressure engine the pressure of the water only is util ized to drive a piston in a cylinder. In some forms the action of the piston is reciprocating and in others rotary. In all of them the actual amount of pressure expended is only that which is needed to impart motion to the fluid to fol low the piston and escape from the cylinder, and, therefore, the greatest efficiency is obtained by making the piston as small as practicable and using a large pressure. The majority of them are of the reciprocating, low-speed type, and are particularly useful as secondary motors for operating the opening machinery of various forms of swing, draw and lifting or rolling bridges, and in connection with cranes and va rious forms of hydraulic lifts.
For futher detailed information relative to the construction, operation and application of the various forms of engines, consult the arti cles under the titles AUTOMOBILE; AEROPLANE; INTERNAL COMBUSTION ENGINE; LOCOMOTIVES; MOTOR; PUMPS AND PUMPING MACHINERY; Ro