Newcomen steam engine
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Image:Newcomen atmospheric engine animation.gif Image:Newcomen6325.png Thomas Newcomen's atmospheric engine, 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 to pump water out of mines starting in the early 18th century, and were the basis for James Watt's later improved versions. Although Watt is far more famous today (due largely to Matthew Boulton's tireless salesmanship), Newcomen rightly deserves the majority of the credit for the widespread introduction of steam power.
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.
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 syphon, 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.
Several other experimenters attempted to provide mechanical work from existing engine designs. One of the most interesting was that of Denis Papin, who used a steam pump similar to Savery's and then ran the water over a water wheel. However a system that directly provided the work without the need for water would be a great improvement.
This problem was solved by Newcomen. He conceived the idea of a 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 pump at the bottom of the mine would be operated by the motion of the beam.
In 1711, his first commercial engine was completed, replacing a team of 500 horses. In 1712, Newcomen and John Calley built their first engine on top of a water-filled mine shaft to demonstrate its power, pumping it out in hours. It was used later that year at the Conygree Coalworks near Dudley in the West Midlands and a working replica can today be seen at the Black Country Living Museum nearby. 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 shared the patent due to his use of the water spray. Although its first use was in a coal-mining area, Newcomen's engine would find its greatest use pumping water out of the mineral mines in his native West Country, such as the tin mines of Cornwall.
By the time of his death, Newcomen had installed over a hundred of his engines, not only in the West Country and the Midlands but also in north Wales and Cumbria.
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. It should be noted that 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. 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.
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 cylider 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. Richard Arkwright, for example, even attempted to use a Newcomen engine to pump water to power a waterwheel!
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.
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