THE PRINCIPLE OF THE INJECTOR’S ACTION.
The principle of the injector’s action is that of induced currents, which is much more popularly understood to-day than it was twenty-five years ago. A current of any kind has a tendency to induce a movement in the same direction of any body it passes over or touches. Thus, we are all familiar with the fact that a current of air called wind, passing over the surface of a body of water, sets waves in motion, and dashes the water high up on the shore above its original level. In the same way, a jet of steam moving very rapidly, when injected into a body of water under favorable conditions, imparts a portion of its motion, and starts momentum sufficient to overcome the original pressure of the steam. That is how the injector is made to force water into a boiler against the same pressure the steam is starting from. The principle is now utilized in the arts for many useful purposes. The ordinary locomotive blast, blowers, steam siphons, steam-jets, jet exhausters, and argand burners, are common instances of its application.
When the action of the injector is closely examined, its mystery as a source of power disappears; for it is found that an amount of heat equal to the mechanical equivalent of work done, is used up during the operation of feeding. Thus, when a given quantity of heat units pass from the throttle to work the injector, the whole of the heat does not return to the boiler along with the feed-water, as was first supposed to be the case; but a portion of heat representing the foot pounds of work done is dissipated, besides other losses incident to leakage, radiation, and convection.