The Locomotive Of Today

The Boiler ; Feed Pumps and Injectors. 51 The supply of water to the boiler is maintained either by means of injectors or pumps,the former beingworked by steam, either high pressure or exhaust, and the latter generally from some moving part of the engine. Brie fly, the principle of the injectors action is as folio ws : A jet of steam issuing from a contracted nozzle under a given pressure possesses more velocity than a corresponding jet of water would do at the same pressure, and if a jet of steam is suddenly brought into contact with a flow of water, a portion of the steam is con- densed, and its velocity becomes imparted to the water to a sufficient extent to enable the combined steam and water to lift the clack valve and enter the boiler. It is necessary that the water should not be too hot, as the jet of steam would then pass completely through it without condensing, and would not be able to enter the boiler at all; on the other hand, the colder the water the better the injector will work. As, however, the aim of all designers of boilers is to get heated water into them, and so avoid local straining, due to expansion and contraction at those points where the colder water is introducecl, improvements have been made in injectors enabling them to work with warm and even hot water. The earliest form of injector was invented by Giffard, and first fitted to locomotives in 1859, and the original form, slightly modified, has survived to the present day, a num- ber of engines still carrying them. A common pattern is shown at A, Fig. 10, standing vertically. It has three arms and an open base, being there fitted with a non-return valve; inside are three sets of cones, the top one being tor steam, which enters through the top branch, the second cone is in communication with the water, which linds admission through the next branch, and in this the steam meets the water, and is condensed; the third cone, which has its small end towarcls the small end of the last mentioned, with a space between, where the third branch is in communication, is provided as an outlet for all water and steam that does not correctly pass the opening between the two cones, and is called the overflow. To start the injector, water is turned on at the feed cock on the tank, then steam is admitted, and the quantity regulated by means of the screw plug shown inside the steam cone; the water is controlled by the raising or lowering of the combining cone by means of the hånd wheel which is attacheel to the pinion engaging the rack on it. These are adjusted until there is no overflow, and the injector is then fully at work. The non-return valve at the foot is placed there to prevent any steam or water from blowing- back if the boiler