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tem of machinery. The total area of the diagram represents the maximum energy that could be obtained, theoretically, frum the steam, if it were expanded down to the pressure in the condenser. The area enclosed by lines A, B, C, D, and E, shows the theoretical maximum energy realizable in a quadruple engine from 260 Ibs. pressure to 26 in. vacuum, and the area cross-hatched the additional energy that can be utilized in a turbine, but which TAE MarINne REVIEW higher pressure, if necessary, to meet the conditions required, From an estimate of the theoretical efficiency under the var- ious conditions of pressure as set forth in the following table, it would appear, apart from any practical considerations, that there is nothing to choose between an initial pressure at the turbine of between 7 lbs: and 15 Ibs. absolute, any pressure within this limit appearing to give the most economical result. Initial Reciprocating Theoretical B. T. U. pressure engine back per lb. of steam. turbine. pressure. RB. Turbine. Total. Assuming © 200.:ibs. -absolute-at.s.. 0. ss. 15 16 178 142 320 Reciprocating ..eneines clon 66a scerssds sss nes 124% 13% 189 Lat 320 28-in.. 'vacuum: at. Condenser. .¢ 5. wn 6 cet 7 8 218 100 318 cannot be economically used in a recipro- cating engine. In a combination system, the most suit- able initial pressure for the turbine, or the dividing line between the reciprocating engine and the turbine, wil greatly de- pend upon the conditions of service of the particular vessel taken. The reciprocat- ing engine, or engines, could be designed to exhaust at a pressure of netween 8 Ibs. and 16 lbs. absolute, or even at a slightly In the case of a vessel which runs on service continually at or about her design- ed full speed, an initial pressure of about 7 lbs. absolute at the turbine appears most suitable. In a vessel which does part of her running at the designed power. and part at a considerably reduced power, it is desirable to design the turbines so that the initial pressure would not fall below 7 Ibs. absolute when running under the lower conditions of power. FIG. 2: EFFECT OF VACUUM UPON STEAM CONSUMPTION OF TRIPLE-EXPANSION RECIPROCATING ENGINE OF 200 LH.P. © VaAcuuUM. 8 26° Lys. SreamM PER I.H.P. Hovr. 24 22 20° is 4 6 Les. PRESSURE ABSOLUTE. © Fig. 3. EFFECT OF VACUUM UPON STEAM CONSUMPTION OF STEAM TURBINE OF 1,000 K.W. TURBO-GENERATOR. VACUUM, -- " 30 28 26° Las. SreaAM PER K.W. Hovr. -- 24° : = Les. PRESSURE ABSOLUTE. 22 20° is 21 It might be of interest at this stage to consider the disposition of the turbines in combination with reciprocating engines on board ship. The arrangement of the turbine, or turbines, depends greatly upon whether the vessel is to be fitted with single or twin-screw reciprocating engines. With a single reciprocating engine, one turbine, two turbines in "series," or two turbines in "parallel" could be fitted, each turbine driving a separate shaft in addi- tion to the reciprocator shaft. With twin- screw reciprocating engines, an arrange- ment of one turbine in the center of the vessel, two turbines in "parallel," or two turbines in "series," could be adopted The arrangement which seems to com- mend itself generally to shipowners and builders, where twin-screw reciprocating engines are fitted, is the arrangement with the turbine on the center shaft, In 1901 and the two or three follow- ing years, alternative schemes were pre- pared from time to time. Fig. 5 (Platce II) shows an arrangment which was pre- pared in 1901 of a single reciprocating engine in combination with two low-pres- sure turbines in "series." The indicated horsepower of this proposal was 1,500, speed 1114 knots, and loaded displacement 5,300 tons. Fig. 6 shows another arrange- ment of one reciprocating engine, and a turbine on one side of the vessel, The I. H. P. of this vessel was 1,200 total, and the speed 10 knots. The turbines in each proposal were designed for about 25 per cent. of the power, and the reciprocating engines the remainder, the turbines taking the steam from the reciprocating engines at 7 Ibs. absolute pressure. It was estimated that the combination as applied to cargo ves- sels would be about 15 per cent to 20 per cent more economical than the ordinary triple-expansion engines usually fitted to this class of vessel. Owing to the rapid development of the turbine industry for high-speed work, and the attention which was, in conse- quence, paid to this branch of the busi- -- ness generally, the development of the combination system: fell more into the background than its merits and the w'de scope of its application would sezm to have deserved. : About two years ago, at the suggestion of Sir William White, designs were pre- pared of a combination system as applied to the intermediate type of liner of moder- ately large power and speed, and s'1ce that time numerous designs have been prepared for various types of vessels of speeds ranging from 13 to 16 knots. By the courtesy of Messrs. Swan, Hun- ter & Wigham Richardson, who, for a considerable period, have taken much in- terest in this combination of machinery, the figures in the table are given of the comparative sizes of engines, power, etc., of the "combination" as com-