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Steam Engine

Steam engine

A steam engine is a machine that converts the heat energy of steam into mechanical energy. A steam engine passes its steam into a cylinder, where it then pushes a piston back and forth. It is with this piston movement that the engine can do mechanical work. The steam engine was the major power source of the Industrial Revolution in Europe in the eighteenth and nineteenth centuries. It dominated industry and transportation for 150 years.

History

The first steam-powered machine was built in 1698 by the English military engineer Thomas Savery (c. 16501715). His invention, designed to pump water out of coal mines, was known as the Miner's Friend. The machine, which had no moving parts, consisted of a simple boilera steam chamber whose valves were located on the surfaceand a pipe leading to the water in the mine below. Water was heated in the boiler chamber until its steam filled the chamber, forcing out any remaining water or air. The valves were then closed and cold water was sprayed over the chamber. This chilled and condensed the steam inside to form a vacuum. When the valves were reopened, the vacuum sucked up the water from the mine, and the process could then be repeated.

A few years later, an English engineer and partner of Savery named Thomas Newcomen (16631729) improved the steam pump. He increased efficiency by setting a moving piston inside a cylinder, a technique still in use today. A cylindera long, thin, closed chamber separate from the boilerreplaced the large, open boiler chamber. A pistona sliding piece that fits in the cylinderwas used to create motion instead of a vacuum. Steam filled the cylinder from an open valve. When filled, the cylinder was sprayed with water, causing the steam inside to condense into water and create a partial vacuum. The pressure of the outside air then forced the piston down, producing a power stroke. The piston was connected to a beam, which was connected to a water pump at the bottom of the mine by a pump-rod. Through these connections, the movement of the piston caused the water pump to suck up the water.

Words to Know

Condenser: An instrument for cooling air or gases.

Cylinder: The chamber of an engine in which the piston moves.

Piston: A sliding piece that is moved by or moves against fluid pressure within a cylindrical vessel or chamber.

Turbine: An engine that moves in a circular motion when force, such as moving water, is applied to its series of baffles (thin plates or screens) radiating from a central shaft.

Watt's breakthrough

The most important improvement in steam engine design was brought about by the Scottish engineer James Watt (17361819). He set out to improve the performance of Newcomen's engine and by 1769 had arrived at the conclusion: if the steam were condensed separately from the cylinder, the cylinder could always be kept hot. That year he introduced the design of a steam engine that had a separate condenser and sealed cylinders. Since this kept the heating and cooling processes separate, his machine could work constantly, without any long pause at each cycle to reheat the cylinder. Watt's refined steam engine design used one-third less fuel than a comparable Newcomen engine.

Over the next fifteen years, Watt continued to improve his engine and made three significant additions. He introduced the centrifugal governor, a device that could control steam output and engine speed. He made the engine double-acting by allowing steam to enter alternately on either side of the piston. This allowed the engine to work rapidly and deliver power on the downward as well as on the upward piston stroke. Most important, he attached a flywheel to the engine.

Flywheels allow the engine to run more smoothly by creating a more constant load, and they convert the conventional back-and-forth power stroke into a circular (rotary) motion that can be adapted more readily to power machinery. By 1790, Watt's improved steam engine offered a powerful, reliable power source that could be located almost anywhere. It was used to pump bellows for blast furnaces, to power huge hammers

for shaping and strengthening forged metals, and to turn machinery at textile mills. More than anything, it was Watt's steam engine that speeded up the Industrial Revolution both in England and the rest of the world.

High-pressure engines

The next advance in steam engine technology involved the realization that steam itself, rather than the condensing of steam to create a vacuum, could power an engine. In 1804, American inventor Oliver Evans (17551819) designed the first high-pressure, non-condensing engine. The engine, which was stationary, operated at 30 revolutions per minute and was used to power a marble-cutting saw. The high-pressure engines used large cylindrical tanks of water heated from beneath to produce steam.

Steam was successfully adapted to power boats in 1802 and railways in 1829. Later, some of the first automobiles were powered by steam. In the 1880s, the English engineer Charles A. Parsons (18541931) produced the first steam turbine. By 1900, the steam engine had evolved into a highly sophisticated and powerful engine that propelled huge ships on the oceans and ran turbogenerators that supplied electricity.

Once the dominant power source, steam engines eventually declined in popularity as other power sources became available. Although there were more than 60,000 steam cars made in the United States between 1897 and 1927, the steam engine eventually gave way to the internal-combustion engine as a power source for vehicles.

[See also Diesel engine; Internal-combustion engine; Jet engine ]

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steam-engines

steam-engines are machines employing steam pressure and condensation to generate motion. Thomas Savery's device (1698) pumped water by partial vacuum, without moving parts, and while engines on his principles were still in use in the 1790s, Newcomen's atmospheric cylinder/piston engine erected near Dudley in 1712 established the fundamental principles of steam power. James Watt's separate condenser of 1769 (and reciprocation from 1782) became a source of much-improved technical efficiency once Wilkinson's improved cylinder boring became available (1774), and expressed itself in economy of coal use: by the 1790s Watt engines consumed 70 per cent of the fuel of a comparable Smeaton atmospheric device. Higher capital costs meant that coal prices determined the adoption of Watt technology, and industry located onto the cheapest available coal, still providing half its steam-power in 1800 with atmospheric engines.

Mine drainage was its primary application, where coals were cheap and many engines ran on unsaleable slack, with brewing and milling, water supply, and textiles following, the last before the 1820s often employing stationary steam-power through water-wheels for the even torque needed by early machinery. Wider applications from the 1790s owed more to Trevithick's high-pressure non-condensing and direct acting engines, which powered the first successful marine applications with Symington's Charlotte Dundas (1802—though experimentally proven by Jouffroy at Lyons in 1781), and his validation of the steam carriage (1801) and locomotive (1804). Steam was proven at sea by the voyage of Dodd's Thames from Glasgow to London (1815) and entered general coastal service during the 1820s; and on railways by the Rainhill trials of 1829.

Steam-power in cotton more than doubled 1835–56, and was followed by woollens and linen; the Cornish boiler diffused to produce high pressures at reduced fuel costs; and Stephenson long-boiler and Kitson outside-frame locomotives established the basic pattern of railway motive power. From the Grand Junction's establishment of Crewe (1837), British railways manufactured their own locomotives, with occasional purchases from specialists such as Beyer Peacock, who were otherwise confined to export markets, producing long-term losses in standardization and technical progress. The economical compound steam-engine was little used on British railways, where coal was cheap, whereas it became a standard unit for factory power, and in its ultimate triple-expansion form (after 1880) the key to British shipping and shipbuilding dominance. From the early 1900s, Parsons's marine steam turbine provided still greater speed and economy. Plentiful coal supplies, and the extensive coal/steam engineering industrial base, hereafter represented elements of inertia slowing Britain's adoption of electricity and internal combustion.

J. A. Chartres

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steam engine

steam engine, machine for converting heat energy into mechanical energy using steam as a medium, or working fluid. When water is converted into steam it expands, its volume increasing about 1,600 times. The force produced by the conversion is the basis of all steam engines. Steam engines operate by having superheated steam force a piston to reciprocate, or move back and forth, in a cylinder. The piston is attached by a connecting rod to a crankshaft that converts the back-and-forth motion of the piston to rotary motion for driving machinery. A flywheel attached to the crankshaft makes the rotary motion smooth and steady. The typical steam engine has an inlet valve at each end of the cylinder. Steam is admitted through one inlet valve, forcing the piston to move to the other end of the cylinder. This steam then exits through an exhaust valve. Steam from the other inlet valve then pushes the piston back to its original position, and the cycle starts again. In a single-cylinder steam engine the exhaust steam is usually expelled directly into the atmosphere. A compounded steam engine has several cylinders, which the steam passes through successively until, leaving the last cylinder, it is condensed into water and returned to the boiler. From the Greek inventor Heron of Alexandria to the Englishmen Thomas Newcomen and John Cawley, many persons contributed to the work of harnessing steam. However, James Watt's steam engine, patented in 1769, provided the first practical solution. Earlier engines depended on atmospheric pressure to push the piston into the cylinder, where a vacuum was created by sudden cooling of its steam content. Watt's use of a separate condenser resulted in a 75% saving in fuel. It also made possible the use of steam pressure to move the piston in both directions. Watt's continuing efforts produced a governor, a mercury steam gauge, and a crank-flywheel mechanism, all of which prepared the steam engine for a major role in the Industrial Revolution. Sailing vessels gave way to steamboats, and stagecoaches yielded to railroad trains as the steam engine was perfected. Transmitted by belts, ropes, shafts, pulleys, and gears, the energy from steam engines drove machines in factories and mills. Now, however, steam engines have been replaced in most applications by more economical and efficient devices, e.g., the steam turbine, the electric motor, and the internal-combustion engine, including the diesel engine. They are still sufficiently economical to be used in industries where steam is necessary for some purpose in addition to that of driving an engine.

See C. W. Pursell, Early Stationary Steam Engines in America (1969); E. Robinson, James Watt and the Steam Revolution (1969); see also bibliography under locomotive.

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steam engine

steam engine Engine powered by steam. Steam, generated by heating water, is used to produce movement. In some engines, the steam forces pistons to move along cylinders. This results in a reciprocating (back-and-forth) motion. A mechanism usually changes this into rotary motion. Steam locomotives use reciprocating engines. Steam turbines are engines that produce rotary motion directly by using the steam to turn sets of fan-like wheels. In any steam engine, some of the heat used to turn water into steam in a boiler converts into energy of motion. The heat may be produced by burning fuel in a furnace, or may come from a nuclear reactor. The first steam engine, invented by Thomas Savery in 1689, was a form of pump, used to remove water from mines. In 1712, Thomas Newcomen invented a steam-operated pump with pistons. From the 1760s, James Watt improved on Newcomen's ideas and produced more efficient steam engines. This led to the use of steam engines to power machinery in factories. In 1884, English engineer Charles Parsons invented the first practical steam turbine. His machines were so efficient that turbines soon started to replace reciprocating steam engines in power stations.

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steam engine

steam en·gine • n. an engine that uses the expansion or rapid condensation of steam to generate power. ∎  a steam locomotive.

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Steam Engine

Steam Engine

History

The workings of a steam engine

Resources

A steam engine is a machine that converts the heat energy of steam into mechanical energy by means of a piston moving in a cylinder. As an external combustion enginesince it burns its fuel outside of the enginea steam engine passes its steam into a cylinder where the steam then pushes a piston back and forth. It is with this piston movement that the engine can do mechanical work. The steam engine was the major power source of the Industrial Revolution (that began in England in the eighteenth century) and dominated industry and transportation for 150 years. It is still useful today in certain situations and in many developing countries.

History

The earliest known steam engines were the novelties created by Greek engineer and mathematician Hero (Heron) of Alexandria (c. 1070) who lived during the first century AD. His most famous invention was called the aeliopile. This invention was a small, hollow sphere to which two bent tubes were attached. The sphere was attached to a boiler that produced steam. As the steam escaped from the spheres hollow tubes, the sphere itself would begin to whirl and rotate. Hero and several other Greeks designed many other steampowered devises, such as a steam organ and automatic doors, but always in the context of playfulness and seemingly without any interest in using steam in a practical way. Nonetheless, their work established the principle of steam power and their playful devices were a real demonstration of converting steam power into some kind of motion.

Although the Greeks established the principle of steam power, it lay ignored for over 1,500 years until the late 1600s in Europe. During this long period, the main sources of power were first, human muscle power or draft animals, and later, wind and water power. Windmills and waterwheels were adequate for slow, repetitive jobs like grinding corn, in which an interruption of power was of little consequence. However, for some jobs, like pumping water from a mineshaft, a power source that could cease at any time was not always satisfactory. In fact, the very deepness of English mines spurred engineers to search for pumps that were quicker than the old water pumps. By the midsixteenth century, work on air pumps had established the notion of a piston working in a cylinder, and around 1680, French physicist Denis Papin (1647 1712) put some water at the bottom of a tube, heated it, converted it to steam, and saw that the expanded steam pushed forcibly and moved a piston just ahead of it. When the tube cooled, the piston returned to its previous position. Although Papin was well aware he had created an engine that could eventually do work, he was deterred by the very real mechanical difficulties of his time and chose to work on a smaller scale creating the worlds first pressure cooker.

Following Papin, English military engineer Thomas Savery (c.16501715) built what most regard as the first practical steam engine. Unlike Papins system, this machine had no piston since Savery wanted only to draw water from the coal mines deep below the Earth. Knowing that he could use steam to produce a vacuum in a vessel, he connected such a vessel to a tube leading into the water below. The vacuum then drew water up the tube and blew it out by steam pressure. Saverys system was called the Miners Friend as it raised water from the mines using the suction produced by condensing steam. A few years later, English engineer, and partner of Savery, Thomas Newcomen (16631729) improved the steam pump by reintroducing the piston. By 1712, he had built an engine that used steam at atmospheric pressure (ordinary boiling water) and that was fairly easy to build. His piston engine was very reliable and came into general use in England around 1725. His machine was called a beam engine because it had a huge rockingarm or seesaw beam at its top whose motion transferred power from the engines single cylinder to the water pump.

Understanding how the Newcomen engine worked provides insight into all later steam engines. First, the entire machine was contained in an engine house, about three stories high, out of whose top wall poked a long oak beam that could rock up and down. The house was constructed off to the side of the mineshaft. At the bottom of the shaft was the water pump, which was connected to the engine by a long pumprod. Below the beam inside the house was a long brass cylinder, which sat atop a brick boiler. The boiler was fed by coal and supplied the steam. Inside the cylinder was the piston that could slide up and down and was connected to the beam above. The engine always started with the piston in the up position. Then, steam filled the cylinder from an open valve. When filled, the cylinder was sprayed with water, which caused the steam inside to condense into water and create a partial vacuum. With this invention, the pressure of the outside air would force the piston down, which rocked the beam and pulled up the pump rods and sucked up about 12 gal (45 l) of water. The piston then returned to its starting position (up) in the cylinder and the process was repeated. Besides being called a beam engine, Newcomens engine was also called an atmospheric engine since it used air pressure to move the piston (down).

The most important improvement in steam engine design was brought about by Scottish engineer James Watt (17361819). In 1763, Watt was asked to repair a Newcomen engine and was struck by what he considered its inefficiency. He set out to improve its performance and by 1769 had arrived at the conclusion that if the steam were condensed separately from the cylinder, the latter could always be kept hot. That year he introduced a steam engine with a separate condenser. Since this kept the heating and cooling processes separate, his machine could work constantly without any long pause at each cycle to reheat the cylinder. Watt continued to improve his engine and made three additions that were highly significant. First, he made it double acting by allowing steam to enter alternately on either side of the piston. This allowed the engine to work rapidly and deliver power on the downward as well as on the upward piston stroke. Second, he devised his sunandplanet gearing that was able to translate the reciprocal, or toandfro motion of the beam into rotary motion. Third, he added a centrifugal governor that maintained a constant engine speed despite varying loads. This highly innovative device marks the early beginnings of automation, since Watt had created a system that was essentially selfregulating. Watt also devised a pressure gauge that he added to his engine. By 1790, Watts improved steam engines offered a powerful, reliable power source that could be located almost anywhere. This meant that factories no longer had to be situated next to water sources, but could be built closer to both their raw materials and transport systems. More than anything, it was Watts steam engine that speeded up the Industrial Revolution both in England and the rest of the world.

Watts steam engine was not perfect, however, and did have one major limitation; it used steam at low pressure. Highpressure steam meant greater power from smaller engines, but it also meant extreme danger since explosions of poorly made boilers were common. The first to show any real success with it was English inventor Richard Trevithick (17711833). By the end of the eighteenth century, metallurgical techniques were improving and Trevithick believed he could build a system that would handle steam under high pressure. By 1803, Trevithick had built a powerful, highpressure engine that he used to power a train. His technical innovations were truly remarkable, but highpressure engines had earned such a bad reputation in England that twenty years would pass before English inventor George Stephenson (17811848) would prove their worth with his own locomotives.

In the United States however, there was little bias against, or hardly any knowledge of, steam power. Toward the end of the eighteenth century, Evans began work on a highpressure steam engine that he could use as a stationary engine for industrial purposes and for land and water transport. By 1801, he had built a stationary engine that he used to crush limestone. His major highpressure innovation placed both the cylinder and the crankshaft at the same end of the beam instead of at opposite ends. This allowed him to use a much lighter beam.

Over the years, Evans built some 50 steam engines that were not only used in factories, but also to power an amphibious digger. Highpressure steam ran this oddlooking scow that was a dredge that could move on land as well as in water. It was the first powered road vehicle to operate in the United States.

Despite Evans hard work and real genius, his innovative efforts with steam met with little real success during his lifetime. He was often met with indifference or simple reluctance on the part of manufacturers to change their old ways and convert to steam. His use of steam for land propulsion was set back by poor roads, vested interest in horses, and woefully inadequate materials. After Evans, highpressure steam became widely used in America, unlike England where Watts lowpressure engines took a long time to be replaced. But improvements were made nonetheless, and iron would eventually replace timber in engine construction, and horizontal engines came to be even more efficient than the old vertical ones.

The workings of a steam engine

Throughout all of this development and improvement of the steam engine, no one really knew the science behind it. All of this work had been accomplished on an empirical basis without reference to any theory. It was not until 1824 that this situation changed with the publication of Reflexions sur La Puissance Motrice du Feu by French physicist, Nicolas Leonard Sadi Carnot (17961832). In his book On the Motive Power of Fire, Carnot founded the science of thermodynamics (or heat movement) and was the first to consider quantitatively the manner in which heat and work are related. Defining work as weight lifted through a height, he attempted to determine how efficient or how much work a Watt engine could produce. Carnot was able to prove that there was a maximum theoretical limit to the efficiency of any engine, and that this depended upon the temperature difference in the engine. He showed that for high efficiency, steam must pass through a wide temperature range as it expands within the engine. Highest efficiency is achieved by using a low condenser temperature and a high boiler pressure. Steam was successfully adapted to power boats in 1802 and railways in 1829. Later, some of the first automobiles were powered by steam, and in the 1880s, English engineer Charles A. Parsons (1854 1931) produced the first steam turbine. This highpowered, highly efficient turbine could produce not only mechanical energy but electrical energy as well. By 1900, the steam engine had evolved into a highly sophisticated and powerful engine that propelled huge ships in the oceans and ran turbogenerators that supplied electricity.

Once the dominant power source, steam engines eventually declined in popularity as other power sources became available. Although there were more than 60,000 steam cars made in the United States between 1897 and 1927, the steam engine eventually gave

KEY TERMS

Condenser An instrument for compressing air or gases.

Cylinder The chamber of an engine in which the piston moves.

Governor A mechanical regulating device that functions automatically and allows for selfregulation of an engines speed.

Piston A sliding piece that is moved by or moves against fluid pressure within a cylindrical vessel or chamber.

way to the internal combustion engine for vehicle propulsion. Today, interest in steam has revived somewhat as improvements make it increasingly efficient and its lowpollution factors make it more attractive.

See also Diesel engine; Jet engine.

Resources

BOOKS

Hindle, Brooke and Steven Lubar. Engines of Change. Washington: Smithsonian Institution Press, 1986.

Lohani, Ashwani. Smoking Beauties: Steam Engines of the World. New Delhi, India: Wisdom Tree, 2004.

Rutland, Jonathan. The Age of Steam. New York: Random House, 1987.

OTHER

History Resources, University of Rochester. The Growth of the SteamEngine.<http://www.history.rochester.edu/steam/thurston/1878/Chapter1.html> (accessed October 29, 2006).

Leonard C. Bruno

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Steam Engine

Steam engine

A steam engine is a machine that converts the heat energy of steam into mechanical energy by means of a piston moving in a cylinder. As an external combustion engine—since it burns its fuel outside of the engine—a steam engine passes its steam into a cylinder where it then pushes a piston back and forth. It is with this piston movement that the engine can do mechanical work. The steam engine was the major power source of the Industrial Revolution and dominated industry and transportation for 150 years. It is still useful today in certain situations.


History

The earliest known steam engines were the novelties created by the Greek engineer and mathematician named Hero who lived during the first century a.d. His most famous invention was called the aeliopile. This was a small, hollow sphere to which two bent tubes were attached. The sphere was attached to a boiler that produced steam. As the steam escaped from the sphere's hollow tubes, the sphere itself would begin to whirl and rotate. Hero of Alexandria and several other Greeks designed many other steam-powered devises, such as a steam organ and automatic doors, but always in the context of playfulness and seemingly without any interest in using steam in a practical way. Nonetheless, their work established the principle of steam power and their playful devices were a real demonstration of converting steam power into some kind of motion .

Although the Greeks established the principle of steam power, it lay ignored for over 1,500 years until the late 1600s in Europe . During this long period, the main sources of power were first, human muscle power or draft animals, and later, wind and water power. Windmills and waterwheels were adequate for slow, repetitive jobs like grinding corn, in which an interruption of power was of little consequence. However, for certain jobs, like pumping water from a mine shaft, a power source that could cease at any time was not always satisfactory. In fact, it was the very deepness of the English mines that spurred engineers to search for pumps that were quicker than the old water pumps. By the mid-sixteenth century, work on air pumps had established the notion of a piston working in a cylinder, and around 1680, the French physicist Denis Papin (1647-1712) put some water at the bottom of a tube, heated it, converted it to steam, and saw that the expanded steam pushed forcibly and moved a piston just ahead of it. When the tube cooled, the piston returned to its previous position. Although Papin was well aware he had created an engine that could eventually do work, he was deterred by the very real mechanical difficulties of his time and chose to work on a smaller scale-creating the world's first pressure cooker.

Following Papin, an English military engineer, Thomas Savery (c.1650-1715), built what most regard as the first practical steam engine. Unlike Papin's system, this had no piston since Savery wanted only to draw water from the coal mines deep below the earth . Knowing that he could use steam to produce a vacuum in a vessel, he connected such a vessel to a tube leading into the water below. The vacuum then drew water up the tube and blew it out by steam pressure. Savery's system was called the "Miner's Friend" as it raised water from the mines using the suction produced by condensing steam. A few years later, an English engineer and partner of Savery named Thomas Newcomen (1663-1729) improved the steam pump by reintroducing the piston. By 1712 he had built an engine that used steam at atmospheric pressure (ordinary boiling water) and which was fairly easy to build. His piston engine was very reliable and came into general use in England around 1725. His machine was called a beam engine because it had a huge rocking-arm or see-saw beam at its top whose motion transferred power from the engine's single cylinder to the water pump.

Understanding how the Newcomen engine worked provides insight into all later steam engines. First, the entire machine was contained in an engine house, about three stories high, out of whose top wall poked a long oak beam that could rock up and down. The house was constructed off to the side of the mine shaft. At the bottom of the shaft was the water pump which was connected to the engine by a long pump-rod. Below the beam inside the house was a long brass cylinder which sat atop a brick boiler. The boiler was fed by coal and supplied the steam. Inside the cylinder was the piston that could slide up and down and was connected to the beam above. The engine always started with the piston in the up position. Then steam filled the cylinder from an open valve. When filled, the cylinder was sprayed with water which caused the steam inside to condense into water and create a partial vacuum. With this, the pressure of the outside air would force the piston down, which rocked the beam and pulled up the pump rods and sucked up about 12 gal (45 l) of water. The piston then returned to its starting position (up) in the cylinder and the process was repeated. Besides being called a beam engine, Newcomen's engine was also called an atmospheric engine since it used air pressure to move the piston (down).

The most important improvement in steam engine design was brought about by the Scottish engineer James Watt (1736-1819). In 1763, Watt was asked to repair a Newcomen engine and was struck by what he considered its inefficiency. He set out to improve its performance and by 1769 had arrived at the conclusion that if the steam were condensed separately from the cylinder, the latter could always be kept hot. That year he introduced a steam engine with a separate condenser. Since this kept the heating and cooling processes separate, his machine could work constantly without any long pause at each cycle to reheat the cylinder. Watt continued to improve his engine and made three additions that were highly significant. First, he made it double-acting by allowing steam to enter alternately on either side of the piston. This allowed the engine to work rapidly and deliver power on the downward as well as on the upward piston stroke. Second, he devised his sun-and-planet gearing which was able to translate the reciprocal , or to-and-fro motion of the beam into rotary motion. Third, he added a centrifugal governor that maintained a constant engine speed despite varying loads. This highly innovative device marks the early beginnings of automation , since Watt had created a system that was essentially self-regulating. Watt also devised a pressure gauge that he added to his engine. By 1790, Watt's improved steam engines offered a powerful, reliable power source that could be located almost anywhere. This meant that factories no longer had to be sited next to water sources, but could be built closer to both their raw materials and transport systems. More than anything, it was Watt's steam engine that speeded up the Industrial Revolution both in England and the rest of the world.

Watt's steam engine was not perfect however, and did have one major limitation; it used steam at low pressure. High pressure steam meant greater power from smaller engines, but it also meant extreme danger since explosions of poorly-made boilers were common. The first to show any real success with it was the English inventor Richard Trevithick (1771-1833). By the end of the eighteenth century, metallurgical techniques were improving and Trevithick believed he could build a system that would handle steam under high pressure. By 1803, Trevithick had built a powerful, high-pressure engine that he used to power a train. His technical innovations were truly remarkable, but high-pressure engines had earned such a bad reputation in England that twenty years would pass before English inventor George Stephenson (1781-1848) would prove their worth with his own locomotives.

In the United States however, there was little bias against, or hardly any knowledge of, steam power. Toward the end of the eighteenth century, Evans began work on a high-pressure steam engine that he could use as a stationary engine for industrial purposes and for land and water transport. By 1801, he had built a stationary engine that he used to crush limestone. His major high-pressure innovation placed both the cylinder and the crankshaft at the same end of the beam instead of at opposite ends. This allowed him to use a much lighter beam.

Over the years, Evans built some 50 steam engines which were not only used in factories, but also to power an amphibious digger. High-pressure steam ran this oddlooking scow that was a dredge that could move on land as well as in water. It was the first powered road vehicle to operate in the United States.

Despite Evans' hard work and real genius, his innovative efforts with steam met with little real success during his lifetime. He was often met with indifference or simple reluctance on the part of manufacturers to change their old ways and convert to steam. His use of steam for land propulsion was set back by poor roads, vested interest in horses , and woefully inadequate materials. After Evans, high-pressure steam became widely used in America, unlike England where Watt's low-pressure engines took a long time to be replaced. But improvements were made nonetheless, and iron would eventually replace timber in engine construction, and horizontal engines came to be even more efficient than the old vertical ones.

The workings of a steam engine

Throughout all of this development and improvement of the steam engine, no one really knew the science behind it. Basically, all of this work had been accomplished on an empirical basis without reference to any theory. It was not until 1824 that this situation changed with the publication of Reflexions sur La Puissance Motrice du Feu by the French physicist, Nicolas Leonard Sadi Carnot (1796-1832). In his book On the Motive Power of Fire, Carnot founded the science of thermodynamics (or heat movement) and was the first to consider quantitatively the manner in which heat and work are related. Defining work as "weight lifted through a height," he attempted to determine how efficient or how much "work" a Watt engine could produce. Carnot was able to prove that there was a maximum theoretical limit to the efficiency of any engine, and that this depended upon the temperature difference in the engine. He showed that for high efficiency, steam must pass through a wide temperature range as it expands within the engine. Highest efficiency is achieved by using a low condenser temperature and a high boiler pressure. Steam was successfully adapted to power boats in 1802 and railways in 1829. Later, some of the first automobiles were powered by steam, and in the 1880s, the English engineer Charles A. Parsons (1854-1931) produced the first steam turbine . This high-powered, highly efficient turbine could produce not only mechanical energy but electrical energy as well. By 1900, the steam engine had evolved into a highly sophisticated and powerful engine that propelled huge ships in the oceans and ran turbogenerators that supplied electricity .

Once the dominant power source, steam engines eventually declined in popularity as other power sources became available. Although there were more than 60,000 steam cars made in the U. S. between 1897 and 1927, the steam engine eventually gave way to the internal combustion engine for vehicle propulsion. Today, interest in steam has revived somewhat as improvements make it increasingly efficient and its low-pollution factors make it more attractive.

See also Diesel engine; Jet engine.

Resources

books

Hindle, Brooke and Steven Lubar. Engines of Change. Washington: Smithsonian Institution Press, 1986.

Rutland, Jonathan. The Age of Steam. New York: Random House, 1987.


Leonard C. Bruno

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Condenser

—An instrument for compressing air or gases.

Cylinder

—The chamber of an engine in which the piston moves.

Governor

—A mechanical regulating device that functions automatically and allows for self-regulation of an engine's speed.

Piston

—A sliding piece that is moved by or moves against fluid pressure within a cylindrical vessel or chamber.

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