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.

EXHAUST STEAM INJECTORS. 107 Fig. 61 is an external view of the injector illustrated at fig. 60. , Water Control Arrangements.—The water supply to tiie injector is regulated by sliding the steam inlet nozzle a away from or towards the combining nozzle c (see fig. 59) so as to vary the annular water inlet area d between said nozzles. In some cases the steam nozzle is fixed and the combining and discharge nozzles are moved relatively thereto (see fig. 60). . The water is admitted as a thin annular film m order to present as large an area as possible to the steam for con- densation purposes. . Action of Exhaust Injector.—The velocity ox the m- coming exhaust steam is entirely dependent upon the degree of vacuum* at the mouth of the steam nozzlø. To produce said vacuum, the presence of both tlie steam ancl water is necessary so that tlie former may be condensed by the latter. The exhaust steam from an engine is generally of sufficient pressure to flow to the injector of itself. With an exhaust injector constructed as shown at tags. 59 ancl 60, the pressure during normal working at the mouth of the steam nozzle is generally about 5 Ibs. to 6 Ibs. per square incli absolute. The velocity of saturated steam at a pressure ot 16 Ibs. per square inch absolute, containing, say, 20 per cent of moisture into a region at a pressure of 6 Ibs. per square inch absolute, is 1,640 ft. per second. We will assunie that 9 Ibs of cold feed water under a head of 2 ft. are mixed with each 1 Ib. of steam. The velocity of the feed water into a region at a pressure of 6 Ibs. absolute will be about 37 ft. per second. The momentum and velocity of the combined steam and water jet is readily obtained as follows: — Momentum of Momentum of _ Momentum ot steam jet water jet combined jet 1 x 1640 + 9 x 37 = 1973 units. * As the degree of vacuum at tlie mouth of the steam nozzle is dependent upon tlie temperature of the feed water by which the steam is condensed, exhaust injectors are unable to deal with liot feed water.