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.

108 THE STKAM INJECTOB. That is the velocity per unit mass (1 Ib.) of the jet is 197 3 ft. per second. If a water jet were discharging from a boiler into a region at an absolute pressure of 6 Ibs. per square inch, then to give said jet a velocity of 197*3 ft. per second, the boiler would require to be under a gauge pressure of about 254 Ibs. per square inch. Thus if we neglect all consideration of losses, an exhaust injector working under the conditions just described should be able to feed a boiler under a pressure of nearly 254 Ibs. per square inch. To illustrate the actual performance of an injector under conditions very similar to those descriLeu, the result of a test is here given : — Exhaust steam pressure. Pounds per square inch absolute. Feed water temperature. Head of Feed water. , 2 feet Delivery temperature. Delivery pressure. Pounds per square inch absolute. 16 Deg. Fah. 60 Deg. Fali. 162 95 The reasons for the low delivery pressure have already been fully discussed. One of the drawbacks of exhaust injectors as made until quite recently lias been the lowness of the maximum de- livery pressure when exhaust steam alone is employed; 80 Ibs. by gauge lias been tlie liighest obtainable under ordinary working conditions. To vary the delivery pressure without altering the con- struction of the injector or the water head, two courses are open, namely: — (1) To increase the water inlet area, so as to ’ncrease the rate of condensation of the steam and intensify the vacuum at the steam nozzle mouth. (2) To recluce the water inlet area, so as to lessen the load which the steam has to carry. Both of these courses can be adopted successfully within narrow limits, but eventually the disadvantages outwedgli the advantages. Thus, if the water supply is increased, there comes a point when the rate of retardation of the velocity of the jet through tlie combining nozzle is greater