Newcomen steam engine

Before the Newcomen steam engine steam had been used only in various devices, called steam fountains, for raising water. In 1706 the first successful attempt to combine the ideas of these devices into an economical and convenient machine was made by Thomas Newcomen This machine was called an atmospheric steam engine. It consisted of a boiler A, in which the steam was generated, and a cylinder B, in which a piston moved. When the valve V was opened, the steam pushed up the piston P. At the top of the stroke, the valve V was closed, the valve V' was opened, and a jet of cold water from the tank C was injected into the cylinder, thus condensing the steam and reducing the pressure under the piston. The atmospheric pressure above then pushed the piston down again.

This machine was used to pump water from mines. It consumed a great deal of fuel, because the cold water cooled the cylinder walls so much that when the steam was turned in, much steam condensed before the piston was raised.

About 1711 Newcomen's engine began to be introduced for pumping mines. It is doubtful whether the action was originally automatic, or depended on the periodical Valve-gear, turning of taps by an attendant. The common story is that in 1713 a boy named Humphrey Potter, whose duty it was to open and shut the valves of an engine he attended, made the engine self-acting by causing the beam itself to open and close the valves by suitable cords and catches. This device was simplified in 1718 by Henry Beighton, who suspended from the beam a rod called the plugtree, which worked the valves by means of tappets. By 1725 the engine was in common use in collieries, and it held its place without material change for about three-quarters of a century in all. Near the close of its career the atmospheric engine was much improved in its mechanical details by John Smeaton, who built many large engines of this type about the year 1770, just after the great step which was to make Newcomen's engine obsolete had been taken by James Watt.

Compared with Savery's engine, Newcomen’s had (as a pumping engine) the great advantage that the intensity of pressure in the pumps was not in any way limited by the pressure of the steam. It shared with Savery’s, in a scarcely less degree, the defect already pointed out, that steam was wasted by the alternate heating and cooling of the vessel into which it was led. Though obviously capable of more extended uses, it was in fact almost exclusively employed, to raise water—in some instances for the purpose of turning water-wheels to drive other machinery. Even contemporary writers complain. of its vast "consumption of fuel", which appears to have been scarcely smaller than that of the engine of Savery.

A working replica of an early Newcomen Engine has been constructed at the Black Country Living Museum in Dudley.

Contains text from 1911 EB. Please update as needed.'

See also: Steam engine, Watt steam engine