The steam-engine and other heat-motors by Creighton William Henry Paul 1859-

Author:Creighton, William Henry Paul, 1859-
Language: eng
Format: epub, pdf
Tags: Steam-engines, Heat-engines
Publisher: New York, J. Wiley & sons; [etc., etc.]
Published: 1909-03-25T05:00:00+00:00

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'ULTIPLE-EXPANSION ENGINES. 301

expansion, however, being that which gave a final pressure equal to the back pressure. In 1840 a Cornish pump was accurately tested, and the water consumption was found to be 24 pounds at 1.5 expansions and 16.5 pounds at 3.5 expansions. This was assumed to prove Watt's theory, and engine-builders gave all the expansion that their form of valve-gear would admit. Gradually it began to be felt that" expansion-engines were expensive engines." From 1840 to 1860 no authoritative experiments were made. At the latter date, Chief Engineer Isherwood, U. S. Navy, published his accurate and elaborate experiments on the U. S. Steamship Michigan, and the losses from initial condensation were revealed. A more intimate knowledge of the facts demonstrated that the Cornish engine experimented upon was working under unsuspected advantages, which accounted for its economy. The working end of its cylinder was not exposed to exhaust temperatures, the admission steam was superheated by excessive wiredrawing, and a live-steam jacket effectively reduced internal condensation.

Rankine's analyses of Isherwood's results showed that the initial condensation depended upon the range of temperature to which the cylinder was subjected, and that by dividing this range among two or more cylinders economy would result. In a double-expansion engine, for instance, all the steam condensed in the first cylinder is re-evaporated, and so is capable of performing work in the next cylinder. The condensation in the second cylinder is due to its own range of temperature, which is far less than it would be in a simple engine having the same range of expansion as the compound engine.

During the next forty years competition caused an interesting struggle in the production of record-breaking engines. Pressures rose with the advance in the art of boiler-making and the advent of mineral oils. Triple- and quadruple-expansion engines naturally followed the advance in pressures. High-speed engines showed a marked economy over slow-speed engines. It was claimed that the large clearance spaces of the former caused no loss, because the clearance space was filled by recompressed steam to the boiler-pressure. It has only been, in recent years that proper consideration has been given to the large losses that may be expected from

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