The Encyclopaedia Britannica; ..A dictionary of arts, sciences and general literature . n and multiple-cylinder engines, the triple-expansion and thequadruple-expansion, are recognized everywherenow as illustrating good practice. The former isemployed very extensively at sea, and especiallyfor long voyages, and the latter is considered, forexceptionally long cruises at steady speed, desira-ble, whenever fuel, as is usual in such cases as thelatter, is particularly costly, either in price or intransportation. Pressures have continually risensince the introduction, about i860, of surface-condens
The Encyclopaedia Britannica; ..A dictionary of arts, sciences and general literature . n and multiple-cylinder engines, the triple-expansion and thequadruple-expansion, are recognized everywherenow as illustrating good practice. The former isemployed very extensively at sea, and especiallyfor long voyages, and the latter is considered, forexceptionally long cruises at steady speed, desira-ble, whenever fuel, as is usual in such cases as thelatter, is particularly costly, either in price or intransportation. Pressures have continually risensince the introduction, about i860, of surface-condensation at sea, and as rapidly as buildersand users could accommodate themselves to thechange and insure safety and certainty in opera-tion of the newer types of engine and their boil-ers. The accompanying diagram shows the ratein the past and the promise of further increasein the immediate future.* The indications are,that early in the twentieth century, steam cansafely be handled at from 300 to 400 pounds per * Manual of the Steavi Engine, Thurston; Vol. I, p. 354. MARINE ENGINES 27. TRIPLE EXPANSION MARINE ENGINE. square inch, and a generation later we may prob-ably see in common use the pressures experimen-tally attained by Perkins in 1824-36, who succeed- HI - 1 1 ii« 1 101 / / t / 1 / ^ / J_J _- ^ II 11 m u 0 1 in u to L 0 • tf ^ ) _ 0 T 1 1 0 r ?OOA dT INCREASE OF STEAM PRESSURES. ed in controlling 500, then 1,000 and finally 1,500and 2,000 pounds per square inch. The sharpbend in the curve, at 1850-60, indicates the periodof transition alluded to above. The triple-expansion engine usually consists,as a whole, of three similar simple engines sideby side, so arranged as to size of cylinder anddisposition of pipes and valves that they work asa series. There are, however, a number of successfularrangements of three and of four cylinder en-gines driving but two cranks in which the tan-dem disposition of cylinders is adopted withgood results. The engraving represents one set
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