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.

116 THE STEAM INJECTOR. The exhaust steam from an engine contains a certain proportion of oil or grease suspended therein, and as it is very undesirable to allow any grease to pass into the boiler with the feed water on account of its injurious effects upon the boiler plates and tubes, grease separators are often fitted on tlie steam pipe between the engine and the injector. As a rule, however, grease separators are not •employed except upon locomotives. The general method of fitting up an exhaust injector with a supplementary live steam portion on a locomotive is illustrated at fig. 65. The great saving efi’ected by tlie use of exhaust injectors in connection with non-condensing engines will be readily appreciated by simple calculations according to formula (xxx.). The exhaust steam utilised in the injector not only represents the saving of a great number of heat units, but also the saving of a large quantity of water—both points of great importance. As an example of the economy to be effected by the use of an exhaust injector, suppose the steam boiler being fed by the latter to be working at 120Ibs. per square inch abso- lute, wliilst the feed water supplied to tlie injector is at GO <leg. Fah, and suppose that the latter water is pumpeel directly into tlie boiler at a temperature of 60 deg; Fah., then the total heat units above 32 deg. Fah. required from the boilei' furnace to evaporate 1 ]b. of the water at a pressure of 120 Ibs. absolute are 1,158. If now tlie feed water be passed through the injector and be lieated to 168 deg. Fah., then tlie boiler furnace will have to give only 1,0'50 heat units to evaporate 1 Ib. of the water at 120 Ibs. absolute pressure. This represents a gain of 108 units of heat or 9'3 per cent. A saving of 10 per cent in coal con- sumption is generally reckoned as the result of the employ- ment of an exhaust injector. L’ess cold water will, of course, be drawn from the feed tank; as tlie exhaust steam provides about one-ninth of the total'water delivered into the boiler.