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A History of the Growth of the Steam-Engine

The introduction of higher steam and greater expansion


The

value of high pressures and considerable expansion was recognized as long ago as in the early part of the present century, and Watt, by combining skillfully the several principal parts of the steam-engine, gave it very nearly the shape which it has to-day. The compound engine, even, as has been seen, was invented by contemporaries of Watt, and the only important modifications since his time have occurred in details. The introduction of the "drop cut-off," the attachment of the governor to the expansion-apparatus in such a manner as to determine the degree of expansion, the improvement of proportions, the introduction of higher steam and greater expansion, the improvement of the marine engine by the adoption of surface-condensation, in addition to these other changes, and the introduction of the double-cylinder engine, after the elevation of steam-pressure and increase of expansion had gone so far as to justify its use, are the changes, therefore, which have taken place during this last quarter-century. It began then to be generally understood that expansion of steam produced economy, and mechanics and inventors vied with each other in the effort to obtain a form of valve-gear which should secure the immense saving which an abstract consideration of the expansion of gases according to Marriotte's law would seem to promise. The counteracting phenomena of internal condensation and reevaporation, of the losses of heat externally and internally, and of the effect of defective vacuum,
defective distribution of steam, and of back-pressure, were either unobserved or were entirely overlooked.

It was many years, therefore, before engine-builders became convinced that no improvement upon existing forms of expansion-gear could secure even an approximation to theoretical efficiency.

The fact thus learned, that the benefit of expansive working has a limit which is very soon reached in ordinary practice, was not then, and has only recently become, generally known among our steam-engine builders, and for several years, during the period upon which we now enter, there continued the keenest competition between makers of rival forms of expansion-gear, and inventors were continually endeavoring to produce something which should far excel any previously-existing device.

In Europe, as in the United States, efforts to "improve" standard designs have usually resulted in injuring their efficiency, and in simply adding to the first cost and running expense of the engines, without securing a marked increase in economy in the consumption of steam.

SECTION I.--STATIONARY ENGINES.

"STATIONARY ENGINES" had been applied to the operation of mill-machinery, as has been seen, by Watt and by Murdoch, his assistant and pupil; and Watt's competitors, in Great Britain and abroad, had made considerable progress before the death of the great engineer, in its adaptation to its work. In the United States, Oliver Evans had introduced the non-condensing high-pressure stationary engine, which was the progenitor of the standard engine of that type which is now used far more generally than any other form. These engines were at first rude in design, badly proportioned, rough and inaccurate as to workmanship, and uneconomical in their consumption of fuel. Gradually, however, when made by reputable builders, they assumed neat and strong shapes, good proportions, and were well made and of excellent materials, doing their work with comparatively little waste of heat or of fuel.


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