The Steam Injector
A theoretical and practical treatise on the design and operation of injectors and on the flow of fluids through and the design of nozzles.

WATER, CONTROL ARRANGEMENTS, 60 CHAPTER VI Water Control Arrangements. The quantity of steam passing through an injector varies with the pressure of the steam supply. It follows that if it is desired to maintain a fairly constant delivery tempera- ture, and to deliver a maximum quantity of water per pound of steam, the quantity of water supplied to the in- jector must also be varieel at the same time as th© steam pressure varies. Unless this is done, the temperature and pressure of the jet passing through the combining nozzle is- inereased upon an inerease in the steam pressure. Af ter a certain limit is reached the action of the injector becomes unreliable and then ceases, the water not being able to sufficiently condense tlie steam within the limits of the combining nozzle. On the other hånd, if the steam pies- sure fails, the water supply may be too great, and the velocity of the jet passing through the combining nozzle be so reduced as to render that jet unable to overcome the pressure in the boiler being fed. In the earliest Giffard injectors, as illustrated at fig. 1, regulation of the annular water inlet area between the steam nozzle and the combining nozzle was obtaineel by moving the steam nozzle towards or away from the combin- ing nozzle. This method was found in practice to have many objections, the chief being that the necessary pack- ing around the sliding or adjustable steam nozzle was con- tinually requiring to be renewed. The use of the adjustable steam nozzle was finally ob- viated by the introduction in 1864 of a movable combining nozzle. One form of this arrangement is illustrated at fig. 50. The combining nozzle a is ad justed by a rack and pinion or other device to inerease or diminish the annular water inlet area. Injectors having means for adjusting the latter area are known as “ adjusting injectors.” It had also been proposed to control the water supply by a valve or cock placed upon the feed water supply pipc.