All About Engines

IQ2 All About Engines yards deep ! It will be clear from this why manu- facturers who employ only two or three large boilers like to be near a plentiful supply of water. It will be clear, too, why a manufacturing town requires such a tremendous supply of water, and why, for one reason, as we shall see later, the steam which has passed through the engine is frequently condensed Fig. 57.—Principle of injector and returned to the boiler. There is only one way of feeding a number of boilers, and that is by pumps, but single boilers may be fed by an injector, one of the most won- derful contrivances used by the engineer. It was invented by Giffard about fifty years ago, and depends upon two prin- ciples. The first is illustrated by the simple experiment shown in Fig. 57. A vertical tube dips into a vessel of water, and another tube is held hori- zontally so that the end is just over the nearest edge of the vertical tube. When air is blown through the horizontal tube it drags the air in the neighbourhood along with it, creating a reduction of pressure, so that water rises in the vertical tube and may even be blown out in the form of a fine spray. The second principle is that when a jet of steam issues from a suitably designed orifice, it has a velocity enormously greater than water or any other liquid would have