The air-pump, p, for withdrawing the vapor and water from the condenser, the feed-pump, s, for supplying the boilers, and cold-water pump, t, for supplying the condenser cistern, are all worked by rods from the beam; and the governor, u, for maintaining uniformity of motion, is driven by a band from the crankshaft. The above description refers more immediately to that class of steam engines called low-pressure engines.
Types of Engines.—The various forms of the steam engine have received a varied form of classification. There are the general divisions into condensing and non-condensing engines, compound and non-compound, and single, double, or direct acting. Again there is the classification connected with the position of the cylinder, as in the horizontal, vertical, and inclined cylinder engines. Another classification divides steam engines into the uses to which they are applied, such as stationary engines, portable engines, marine, locomotive, electric generating, pumping, mill driving, winding, etc.
Steam Turbine.—The steam turbine, though the most modern form of the steam engine in practice, is the most ancient in actual history, the germ of the invention dating from Hero of Alexandria, in the second century B. C.
FIG. B—BEAM CONDENSING STEAM ENGINE
a, The steam-cylinder; b, the piston; c, the upper steam-port or passage; d, the lower steam-port; ee, the parallel motion; ff, the beam; g, the connecting-rod; h, the crank; ii, the fly-wheel; kk, the eccentric and its rod for working the steam-valve; l, the steam-valve and valve-casing; m, the throttle-valve; n, the condenser; o, the injection-cock; p, the air-pump; q, the hot-well; r, the shifting-valve for creating a vacuum in the condenser previous to starting the engine; s, the feed-pump for supplying the boilers; t, the cold-water pump for supplying condenser cistern; u, the governor.
One kind of steam turbine is really worked on the same principle as a windmill, only steam is used instead of the wind. Instead, however, of the sails making one revolution in seven or eight seconds, it sometimes makes three thousand revolutions a minute, or fifty revolutions a second. In another kind the blades of the turbine are something like the pockets on a water-wheel, and the steam shoves the wheel round by its great velocity.
Turbine engines are now fitted to vessels of large dimensions, up to ocean liners and battleships, with extremely satisfactory results. Turbine engines have also been applied in various other ways, e.g., to the driving of fans and blowers.
The principle of internal combustion, as used in gas and oil engines, has also been applied to the turbine with marked success, and has done much to solve the all-important problem of efficiency. It is extremely improbable that the long-range activities of the submarine would be nearly so effective were it not for the application of the same principle to their engines.