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 =
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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 =
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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.
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