Newcomen atmospheric engine
The atmospheric engine invented by Thomas Newcomen, today referred to as a Newcomen steam engine (or simply Newcomen engine), was the first practical device to harness the power of steam to produce mechanical work. Newcomen engines were used throughout England and Europe principally to pump water out of mines starting in the early 18th century. James Watt's later engine was an improved version. Although Watt is far more famous today, Newcomen rightly deserves the first credit for the widespread introduction of steam power.
Precursors
Prior to Newcomen a number of small steam engines of various sorts had been built, but most were essentially novelties. Around 1600 a number of experimenters used steam to power small fountains, first filling a container with water, then pressurizing it with steam to shoot it out. However these devices could not be scaled up, as the ability to produce large containers for high pressures simply didn't exist.
In 1662 Edward Somerset, second Marquess of Worcester, published a book containing several ideas he had been working on. One was a steam-powered fountain, which used vacuum instead of pressure. In his design two containers would alternately be filled with steam and then allowed to condense to produce a vacuum that would suck up more water from a well. A new charge of steam then pushed the water out as in earlier designs. By running the two containers back to back the fountain could be made somewhat continuous.
Savery's Miner's Friend
In 1698 Thomas Savery introduced a steam powered pump he called the Miner's Friend, essentially identical to Somerset's design and almost certainly a direct copy. Applied to pumping out mines, the water was no longer driven from the cylinder by a new steam charge, but simply allowed to flow out of a valve once the steam condensed and the cylinder was filled. The process of cooling and creating the vacuum was fairly slow, so Savery later added a small water inlet or spray to quickly cool the steam.
Like other vacuum-based pumping systems, Savery's had the problem that it could not lift water more than 32 feet at a time. For deeper mines some sort of mechanical pump needed to be used, one that lifted the water directly instead of "sucking" it up. Such pumps were common already, but required a vertical reciprocating action that Savery's system did not provide.
Savery's invention acted as a kind of siphon, and had no moving parts. Consequently, it cannot really be regarded as the first steam engine, since it could not transmit its power to any external device. There were evidently high hopes for the Miner's Friend, which led Parliament to extend the life of the patent by 21 years, so that the 1699 patent would not expire until 1733. Unfortunately, Savery's device proved much less successful than had been hoped.
Several other experimenters attempted to provide mechanical work from existing engine designs. One of the most interesting was that of Denis Papin, who succeeded in raising a piston by boiling water in a cylinder, and showed that the vacuum created when the steam condensed could lift a heavy weight. However, this was merely a laboratory toy; he failed to develop it into a practical steam pump.
Introduction and spread
Thomas Newcomen developed the principles of Savery and Papin into the beam engine, in which a large wooden beam rocked up and down upon a central fulcrum. Instead of siphoning the water up, as in Savery's engine, a cylinder pump at the bottom of the mine was operated by the motion of the beam. The cylinder was filled with steam from a boiler (usually below it). This was condensed using a jet of water. The resultant vacuum pulled down one end of the beam, thus operating the pump attached to the other.
It is probable that the first Newcomen engine was in Cornwall, but its location is uncertain. This was followed by two in the Black Country, of which the more famous was that erected at the Conygree Coalworks near Dudley, but this was probably preceded by one built a mile and a half east of Wolverhampton. Both these were used by Newcomen and his partner John Calley to pump out water-filled coal mines. A working replica can today be seen at the nearby Black Country Living Museum, which stands on another part of what was Lord Dudley's Conygree Park. Soon orders from wet mines all over England were coming in, and some have suggested that word of his achievement was spread through his Baptist connections.
Since Savery's patent had not yet run out, Newcomen operated under that patent, sicne its term was much longer than any Newcomen could have easily obtained. During the latter years of its currency, the patent belonged to an unincorporated company, The Proprietors of the Invention for raising water by fire.
Although its first use was in coal-mining areas, Newcomen's engine was also used for pumping water out of the metal mines in his native West Country, such as the tin mines of Cornwall. By the time of his death, Newcomen nad others had installed over a hundred of his engines, not only in the West Country and the Midlands but also in north Wales, near Newcastle and in Cumbria.
Technical details
Newcomen's engine consisted of a boiler A, in which the steam was generated. This was usually a haystack boiler, situated directly below the cylinder. It produced low pressure steam, all that the current state of boiler technology could cope with. Steam at this pressure would be unable to move a piston of any size.
One side of the beam was attached by a chain to the pump at the base of the mine, and the chain at the other side suspended a piston within a cylinder B. The cylinder was open at the top end, above the piston P, to the atmosphere. The piston had a bevelled edge, around which hemp rope, kept in place by metal weights, acted as a primitive seal. (The rope was kept wet, so that it would expand against the sides.)
When the valve V was opened, the steam was admitted into the cylinder. After this valve was closed, valve V' was opened to allow cold water from the tank C into the cylinder, thus condensing the steam and reducing the pressure under the piston. The atmospheric pressure above then pushed the piston down in the power stroke.
This raised the working parts of the pump, but their weight immediately returned the beam to its original position. Steam was then readmitted, driving the remains of the condensate out through a one way snifter valve as the process started all over again.
Early versions used manual operation of the valves to work, but the action was slow enough that this was not a serious concern. Later versions used controls attached to the rocking beam to open and close the valves automatically when the beam reached certain positions. 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 (known as the "potter cord"[1]). 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. Towards 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.
While its main use was pumping water out of mines, the Newcomen engine was also used in some places to pump water to drive machinery, for example refilling the upper pool at Coalbrookdale so that there was more water available to drive the blast furnaces, also at Madeley Wood or Bedlam Furnaces and others of the same period (the 1750s. Richard Arkwright, for example, even attempted to use a Newcomen engine to pump water to power a waterwheel.
Successor
The main problem with the Newcomen design was that it was very expensive to operate. After the cylinder was cooled to create the vacuum, the cylinder walls were cold enough to condense some of the steam as it was sprayed in. This meant that a considerable amount of fuel was being used just to heat the cylinder back to the point where the steam would start to fill it again. However, this did not matter very much within the context of a colliery, where coal was freely available. Attempts were made to drive machinery by Newcomen engines, but these were unsuccessful, as the single power stroke produced a very jerky motion.
Newcomen's engine was only replaced when James Watt improved it to avoid this problem (Watt had been asked to repair a model of a Newcomen engine by Glasgow University). In the Watt steam engine, condensation took place in a separate container, attached to the steam cylinder via a pipe. When a valve on the pipe was opened, the vacuum in the condensor would, in turn, evacuate that part of the cylinder below the piston. This eliminated the cooling of the main cylinder, and dramatically reduced fuel use. It also enabled the development of a reciprocating engine, with upwards and downwards power strokes more suited to transmitting power to a wheel.
Watt's design, introduced in 1769, did not eliminate Newcomen engines immediately. Watt's vigorous defence of his patents resulted in the desire to avoid royalty payments as far as possible.
The expiry of the patents led to a rush to install Watt engines in the 1790s, and Newcomen engines were eclipsed - even in collieries. Probably the last Newcomen-style engine to be used commercially – and the last still remaining on its original site – is at Elsecar, near Barnsley in South Yorkshire.
Further reading
- L. T. C. Rolt and J. S. Allen, The Steam Engine of Thomas Newcomen (landmark Publishing, Ashbourne 1997).
See also
External links
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. {{cite encyclopedia}}: Missing or empty |title= (help)
