. A manual of marine engineering: comprising the design, construction, and working of marine machinery. in the two-crank engine, and the necessity for a large receiver modern triple-compound engine is nearly always on the three-crauk 5 66 MANUAL OF MARINE ENGINEERING. principle, and consequently enjoys these advantages to enhance its per-formance. Independently of the advantages of getting steadier motion andreduced stresses on the crank-shaft, there are other reasons which operate inmaking the three-cylinder arrangement a convenient, if not a necessary a rule, the power of
. A manual of marine engineering: comprising the design, construction, and working of marine machinery. in the two-crank engine, and the necessity for a large receiver modern triple-compound engine is nearly always on the three-crauk 5 66 MANUAL OF MARINE ENGINEERING. principle, and consequently enjoys these advantages to enhance its per-formance. Independently of the advantages of getting steadier motion andreduced stresses on the crank-shaft, there are other reasons which operate inmaking the three-cylinder arrangement a convenient, if not a necessary a rule, the power of an engine is obtained more efficiently by onecylinder than by two, and by two than by three; but there is a limit of sizeand weight, beyond which both manufacture and examination when in theship become extremely expensive and difficult, besides the attendant risk,. Fig. 20.—Cylinders of a Two-Crank Quadruple Expansion Engine. and it is for this reason that manufacturers are compelled to go beyond thenumber of two cylinders. Power for power, the three-crank engine took upmore room than the two-crank one, and, except in very large sizes, wasmore expensive to make; but the working parts, piece for piece, are lighter,and more easily made and handled in the ship; and it is of great importanceto reduce the maximum stresses on the shafts of very large engines, to keepthem within the size which may be made with existing appliances, and togive them greater chances of endurance. The cranks are at angles of 120° FOUR-CRANK ENGINES. 67 with one another in the vertical engine, because the cylinders can be madeof such proportions as to admit of this; but in the case of the engines madeby Messrs. Kennie, owing to the two piston-rods for the return connection-rod, there was not that choice of ratios of cylinders, and hence the peculiarpositions of the cranks
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