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.

82 THE STEAM INJECTOR. a head of 2 ft., we should have had to “ subtract ” the 2 ft. instead of to add it, as in this case.) The unbalanced pressure, or the difference between atmospheric pressure and the pressure in the nozzle, is 12 Ibs. per square inch approximately. Taking 1 Ib. pressur© per square inch as the equivalent of a fluid head of 2’3 ft., we obtain the velocity of the incoming feed water as follows:-— Velocity in feet per second = J2 g x head in feet = 76W X (12 x 2-3 +' 2) = 43-66. We have therefore the steam entering the nozzle with a velocity of 3,250 ft. per second, and the water entering witli a velocity of about 44 ft per second. TSie velocity of the water jet resulting from the union of the steam and water is obtained as follows: — M omentum of 4- *4- steam jet 1 x 3250 + Momentum of water jet 15 x 44 16 x velocity = velocity = Momentum of combined jet 3910 units 3910 244 ft. per second. Tlie water je<t issuing from the nozzle has a velocity, therefore, of 244 ft. per second. But the velocity of ä water jet issuing from the boiler supplying steam to the steam jet into a. region, at a pressure of 3 Ibs. per square inch absolut© is, as before stated, only 103 ft. per second, so tliat the combined jet (containinig condensed steam and water in tlie ratio by weigiht of 1 to 15) will readily be a;ble to overcoime a jet teiwling to issue from the boiler, and to itself again enter said boiler. From tlie above the general principles of action of the injector will be readily understood. In aotuial practice the jet issuing from the injector is not moving with a high velocity, but is of high pressure. The relation between velocity and pressure is e^xpressed as