Fig. 516.—See page [252].
After the water commences to flow into the injector it receives motion from the jet of steam; it absorbs heat from the steam and finally condenses it, and thereafter moves on through the forcer tube simply as a stream of water, at a low velocity compared with that of the steam. At the beginning of the forcer tube, it is subjected only to atmospheric pressure, but from this point the pressure increases and the water moves forward under a diminished velocity.
That the condensation of the steam is necessary to complete the process will be evident, for if the steam were not condensed in the combining chamber, it would remain a light elastic body and, though moving at high speed, would have a low degree of energy.
Some injectors are given special names by their makers, such as ejectors and inspirators, but the term injectors is the general name covering the principle upon which all these devices act. The exhaust steam injector is a type different from any of the above-named, in that it uses the exhaust steam from a non-condensing engine. Exhaust steam represents fourteen and seven-tenths (14.7) pounds of work, and when the steam entering the injector is condensed the water is forced into the boiler upon the same general principle as in all injectors.
The injector can be, and frequently is, used as a pump to raise water from one level to another. It has been used as an air compressor, exhauster and also for receiving the exhaust from a steam engine, taking the place, in that case of both condenser and air pump.
The injector is not an economical device, but it is simple and convenient; it occupies a very small space, is not expensive and entirely free from severe strains on its durability; moreover, where a number of boilers are used in one establishment, it is very convenient to have the feeding arrangements separate, so that each boiler may be a complete generating system in itself and independent of its neighbors.
The following text is intended to describe the instruments illustrated on pages 244, 246, 248 and 250.
