Jump To Content

LearnHub




Steam engine

Steam engine
The invention of a vacuum pump in 1654 gave rise to a variety of experiments intended to harness the power of a vacuum, leading to a type of steam engine developed by Thomas Savery (1650?-1715), an English military engineer. His 1698 device, which used a boiler and valves to create suction, was a pump for removing water from Cornish mines. Steam would be created in a boiler, and as the steam expanded, it would be released from a valve. Then the valve would be closed, and the boiler cooled, creating a partially evacuated chamber. Then a valve to the lines down into the mine would be opened and the water pulled up. The system worked to a depth of only 25 feet and was never very practical. Thomas Newcomen (1663-1729) made several improvements to the Savery pump in 1712. He developed a closed cylinder in which a piston was moved by steam pressure. This breakthrough meant that the machine itself could produce motion that could be harnessed through linkages not only to do work but also to open and close valves automatically. Although Newcomen had at first installed valves that were operated by hand, a young boy, Humphrey Potter, developed an automatic system using cords, later replaced by tappet rods suggested by Henry Beighton. Using brass cylinders by 1724 allowed finer tolerances than earlier iron cylinders. The Newcomen engine, linked to a heavy overhead beam, could create a slow, vertical motion that could be harnessed for pumping, running about 10 to 16 strokes per minute. Although James Watt (1736-1819) is often credited as the inventor of the steam engine, he is more properly regarded as the engineer who made a series of design improvements to the existing devices developed by Newcomen, Potter, and Beighton. In 1765 Watt improved the Newcomen engine by adding a condenser, so that the cylinder did not have to be heated and cooled with each stroke. He also added steam valves and a stuffing box to seal the system. Watt brought a somewhat scientific approach to the problems of the Newcomen engine by carefully identifying several inefficiencies that he sought to address. However, a finer boring system was required to produce a well-sealed cylinder, and a machine designed by John Wilkinson in 1775 allowed for a better steam engine with less wasted heat. Watt also added a flywheel to continue the motion of the engine by momentum, a double-action engine that admitted steam to both sides of the piston in 1782, the steam condenser in 1784, and the governor in 1788. Watt's first engines were capable only of linear or vertical motion, but he worked on a method to convert the linear motion to rotary motion. He invented a crank [II] and connecting rod system and a geared system for this purpose. After 1794, the crank linkage became widely used. In <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Britain, the firm of Boulton and Watt maintained a monopoly on steam engine production for 25 years following 1775, and during that time sold more than 500 engines.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

An American, Oliver Evans (1755-1819), who developed a highpressure, noncondensing engine, further improved the steam engine in 1804. Evans built about 50 of his engines, as well as a dredger in 1804 that was probably the first steam-powered land vehicle in the United States. It was amphibious in that it could be moved by paddles in water and by rollers on land. Richard Trevithick (1771-1833) in Britain developed a similar engine and used it to propel the first rail car along a horserail system to and from the Penydarren ironworks at Mehthyr Tydfil in Wales in 1804. Both systems used large cylinders to produce steam piped to the pistons. John Stevens (1749-1838), who developed an early steamboat [IV], improved on the boiler system by running a series of pipes through the firebox, allowing the water to recirculate until it became high-pressure steam. Later designs encased the pipes in a large containing case to prevent damage in case of explosion. The development of many applications for stationary steam engines in the 18th century, and their use early in the 19th century for steamboats, the steam locomotive [IV], and steam-powered carriages led scientists to investigate their behavior and to discover the laws of thermodynamics [IV]. Historians of technology have closely studied the origin of the steam engine because of the central place it held in promoting the Industrial Revolution of the late 18th and the 19th centuries. Like many other major inventions, it represented the combination of many improvements and refinements, dating from Savery's first inefficient steam-powered vacuum pump in 1698 through the modifications of Newcomen, Watts, and others over the following century. In the mid-18th century, British scientists and engineers regarded the two most important technical problems of the era as removing water from mines and developing an accurate method of determining longitude at sea. The steam engine solved the first, and the chronometer solved the second. From the point of view of the application of energy to work, the steam engine was the most significant development since the invention of the waterwheel [II] and the windmill [II] in the late Middle Ages. For a century the steam engine represented such a major force that the period from about 1790 to 1890 is sometimes called the "Age of Steam." Only with the development of the electric motor and electric generator [IV], the internal combustion engine [IV], and the steam turbine [V] was the piston-driven steam engine gradually supplanted as the source of motive power for both transportation and stationary applications.

<?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" />



Your Comment
Textile is Enabled (View Reference)