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.

110 THE STEAM INJECTOR. issuing into a region at an absolute pressure of 2 Ibs. per square inch is about 2,260 ft. per second. We will assumo that with every pound of steam there is mixed 9 Ibs. of water under a head of 2 ft. The velocity of flow of the water under a head of 2 ft. into a region at an absolute pressure of 2 Ibs. per square inch is about 48 ft. per second. The momentum of the combined steam and water jet is obtained as follows : — Momentum of Momentum of _ Momentum <>f steam + water combined jet 1 x 2260 + 9 x 48 = 2692 units. from which the velocity of unit mass (1 Ib.) of the combined jet is given as 269 ft. per second. To produce a water jet discharging into a region at an absolute pressure of 2 Ibs. per square inch with a velocity of 269 ft. per second would require a water pressure (by gauge) of about 470 Ibs. per square inch. Thus an injector working under the above conditions should, if we neglect all consideration of losses, be able to deliver into a boiler under a pressure of nearly 470 Ibs. per square inch. The following test of an injector, of the type illustrated at fig. 62, under conditions very similar to those just considered, will show what the actual performance is: — Exhaust steam pressure. Pounds per square inch absolute. Feed water head. Feed water temperature. Delivery temperature. Delivery pressure. Pounds per square inch absolute. Feet. 2 Deg. Fah. 60 Deg. Fah. 168 135 The important point is that whilst the proportion of water to steam passing through the injector in the test just clealt with is practically the same as in the pre.vious test (as is evidenced by the uniformity of delivery tempera- tures, with the same steam pressures and feed tempera- tures), the actual delivery pressure is increasied from 95 Ibs. to 135 Ibs. per square inch absolute.