. The steam-engine and other heat-motors. 1 1 C____w~ ©• iI <* s8 1 k 0 -H The engines to drive these pumps must have a horse-power equal to Qxh , 33,000 where Q = pounds of water delivered,h=head in feet. 292 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. These engines should develop this power with a pressure equal boiler-pressure * Steam-injector.—Fig. 154 is a diagrammatic sketch of an in-jector. We owe this invention to M. Giffard, a French original invention has been much improved and many care-fully worked out devices have been added to make the device reli-able and
. The steam-engine and other heat-motors. 1 1 C____w~ ©• iI <* s8 1 k 0 -H The engines to drive these pumps must have a horse-power equal to Qxh , 33,000 where Q = pounds of water delivered,h=head in feet. 292 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. These engines should develop this power with a pressure equal boiler-pressure * Steam-injector.—Fig. 154 is a diagrammatic sketch of an in-jector. We owe this invention to M. Giffard, a French original invention has been much improved and many care-fully worked out devices have been added to make the device reli-able and automatic. Its use is practically confined to boiler-feeding, as its efficiency as a pump is very low. As a boiler-feederits thermal efficiency approaches 100%, as all the heat that ittakes from the boiler is returned, but at a lower Fig. 154. The device consists essentially of a steam-nozzle, A; a combin-ing tube, B; and a deli very-tube, D. C is an overflow and E isthe suction-pipe. On page 216 we found that if steam is made to expand adia- batically in a properly proportioned nozzle, the heat lost in expansion was converted into energy of motion, or, in other words, the steam acquired a high velocity. The amount of thermal energy wV2converted into kinetic energy = -^— = wh is more than sufficient to do the work required in forcing Wpounds of feed-water = (12 to 22) w into the boiler against the boiler-pressure, or wh>(W+w) (W+w)hb, where hb is a head of water in feet equivalent to theboiler-pressure Pb. * See Bauer, Marine Engines. SMALL AUXILIARIES. 293 When steam is turned on the injector, the first effect is to driveall air out of the system through the overflow which is open. Thepartial vacuum allows the atmosphere to force water through thesuction-pipe, E, into the combining chamber, B. The stea
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