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.

THE STEAM INJECTOR. CHAPTER I. Introduction. The appliance known to engineers as an injector may be defined as an instrument in which a jet of steam moving at high velocity is caused to carry a jet of water, with which ’t mingles and by which it is condensed, into a boiler or vessel under pressure. The general principles of the injector are based upon cer- tain physical laws expressed in tlie following simple formulæ : — If H represents the head in feet equivalent of the fluid pressure in a boiler, and g the acceleration due to gravity (which may be taken as 32'2 ft. per second per second), then v = 72^H......................(i.) V being the theoretical velocity in feet per second of a jet of such fluid flowing from the boiler. The fluid head equivalent of any pressure depends upon the density of the fluid, and may be expressed thus: — He id in feet — Presssure i*1 P0U11(^8 per square foot weight per cubic foot It follows, therefore, that the velocities of discharge of different fluids under a given pressure (P) vary inversely as the square root of their densities, the relationship being expressed in the following formula : — V = / 2 P_____________(ii.)* V ?/l * It is not strictly accurate to use formula (ii.) for determining the velocity of dischai’ge of an elastic fluid such as steam, as the formula takes no account of the velocity increase due to expansion during discharge. The formula is, however, convenient for determining the approximate relationship between steam and water jets isauing from the same vessel. The case for the steam jet is understated. 2 SI