When an injector receives a sudden shock, such as that produced by the passing of a locomotive over points, it is liable to "fly off"—that is, stop momentarily—and then send the steam and water through the overflow. If this happens, both steam and water must be turned off, and the injector be restarted; unless it be of the self-starting variety, which automatically controls the admission of water to the "mixing-cone," and allows the injector to "pick up" of itself.
For economy's sake part of the steam expelled from the cylinders of a locomotive is sometimes used to work an injector, which passes the water on, at a pressure of 70 lbs. to the square inch, to a second injector operated by high-pressure steam coming direct from the boiler, which increases its velocity sufficiently to overcome the boiler pressure. In this case only a fraction of the weight of high-pressure steam is required to inject a given weight of water, as compared with that used in a single-stage injector.
Chapter II.
THE CONVERSION OF HEAT ENERGY INTO MECHANICAL MOTION.
Reciprocating engines—Double-cylinder engines—The function of the fly-wheel—The cylinder—The slide-valve—The eccentric—"Lap" of the valve: expansion of steam—How the cut-off is managed—Limit of expansive working—Compound engines—Arrangement of expansion engines—Compound locomotives—Reversing gears—"Linking-up"—Piston-valves—Speed governors—Marine-speed governors—The condenser.
Having treated at some length the apparatus used for converting water into high-pressure steam, we may pass at once to a consideration of the mechanisms which convert the energy of steam into mechanical motion, or work.
Steam-engines are of two kinds:—(1) reciprocating, employing cylinders and cranks; (2) rotary, called turbines.
RECIPROCATING ENGINES.
Fig. 17 is a skeleton diagram of the simplest form of reciprocating engine. C is a cylinder to which steam is admitted through the steam-ways3 W W, first on one side of the piston P, then on the other. The pressure on the piston pushes it