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.

PRINCIPLES OF THE 1NJECTOR. 81 The velocity of a jet of water issuing into a. region at a pressure of 3 Ibs. per 'square inch absolute from the boiler (under a pressure of 75 Ibs. per square inch absolute) supplying the steam for the steam jet aforesaid would be an amount due to the fluid head equivalent of the boiler pressure above 3 Ibs. per square inch absolute (i.e., of 72 l)bs. per square inch). Taking 1 Ib. pressure per square inch to be equivalent to a head of 2'3 ft., the total fluid head is ]65‘6ft. Now velocity in feet per second — J2 g x head in feet = 764-4 x 165-6 = 103-2. It will thus be seen thai the oondensed steam jet has a velocity of 3,250 ft. per second, whilst the boiler water jet has a velocity of only 103 ft. per second, the original pres- sures of the steam and water being the same. Obviously if the two jets were directed against one another in a pipe the oondensed steam jet would very easily overcome the boiler water jet and enter the boiler. In this case, hov- ever, we are only delivering back into the boiler what has been takem therefrom. Let us consider the case where, instead of the steam jet being condensed in an extei'nally-cooled nozzle, it is directly mixed with water for the same purpose, and let us assurne that the ratio by weight of the mixture is 15 Ibs of wat-er to 1 Ib. of steam. The wiater av© will assume to be supplied under a head of 2 ft. Assuming tha.t the pressure in the mixing nozzle is main- tained at 3 Ibs. per square inch absolute, due to tihe cotl- densation of tbe ste'atm by the water, the velocity of tli© steaim jet will be, as be<fore, 3,250* ft. per second. The velocity of the water entering the miximg nozzle will Ije an amount due to the head equivalent of the difference between atmospheric pressure plus a head of 2 ft. and the pressurewithin thenozzle. (If the water had been “lifted” to the nozzle through 2 ft. inlstead of being supplied undor 7 si