PRINCIPLE OF THE INJECTOR'S ACTION.
Although the mechanism of the injector is very simple, the philosophy of its action is not so easily understood as the principles on which a pump raises water and forces it into the boiler. On beginning to investigate the action of the injector, it appears a physical paradox, the finding that steam at a given pressure leaves a boiler, passes through several tortuous and contracted passages, raises several check-valves, and then forces water into the boiler against a pressure equal to that which the steam had when it first began the operation. At first acquaintance the operation looks as if it had a strong likeness to perpetual motion, but closer investigation will show that the steam which raises and forces the water by passing through an injector performs mechanical work as truly as the steam that pushes a piston which moves a pump-plunger. A current of any kind, be it steam, air, water, or other matter, has a tendency to induce a movement in the same direction of any body with which it comes in contact. 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 away 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 to the water, and starts it with momentum sufficient to overcome a pressure even higher than the original pressure of the steam. The locomotive blast, blowers, steam siphons, steam jets, jet exhausters, vacuum ejectors, and argand burners, are all common instances of the application of the principle of induced currents.
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