Steam Engine | Research & Encyclopedia Articles

Steam Engine

Simple machines (such as levers, pulleys, inclined planes, screws, wheels and axles, and wedges) have been in use since antiquity; complex machines, though more recent inventions, rely largely on combinations and refinements of these basic machines. Since machines change the direction of work or the force required to perform it, machines need energy to function, whether it derived from animal or human muscle, wind or water currents, or heat-generated energy, such as steam. Steam engines were one of the earliest and most important inventions to convert one form of energy to another. Some historians even credit the steam engine with enabling Europe's industrial revolution, which occurred during the late eighteenth and nineteenth centuries.

The use of steam to power machines initially depended on the ability to create a vacuum. Experiments with vacuums and air pumps began in the 1600s, when the German scientist Otto von Guericke developed a hand-pump that could remove air from sealed containers. Experiments showing that candles would not burn and that a bell's ring could not be heard within such containers proved that a vacuum had been created. In 1654, Guericke more spectacularly demonstrated before the Emperor Ferdinand III that a team of eight horses could nor separate two half-spheres joined together through the force of an internal vacuum.

One of the first steam-powered machines was built in 1698 by the English military engineer Thomas Savery. His invention, designed to pump water out of coal mines and known as the Miner's Friend, was not precisely a steam engine but rather a water pump that used steam and condensation to create a vacuum. Savery's machine, which had no moving parts, consisted of a simple boiler, a steam chamber whose valves were located on the surface, and a pipe leading to the water in the flooded levels of the mine below. The Miner's Friend was based on expansion and suction effects achieved by generating and then condensing steam. Water was heated in the boiler until its steam filled the chamber. This created an expansion that forced out any water or air inside the chamber. A valve was then closed, after which cold water was sprayed over the chamber; this chilled and condensed the steam inside to form the vacuum. When the valves were reopened, water was forced up from the mine, and the process could then be repeated. However, the suction range of this apparatus was only twenty-five feet, and the pump never truly became practical for its intended use in mines.

The French-born British physicist Denis Papin, who was familiar with Savery's pump, also experimented with exploiting the properties of steam to create a mine pump. In 1707, he designed a pump with a moving piston, two receiving chambers, and the first safety valve. Even with these improvements, Papin's design remained inadequate for the large-scale requirements of mining operations.

Further advancements on the Savery pump were made in 1712 by the British engineer Thomas Newcomen, who, with his assistant John Calley, became the first to harness power by setting a moving piston inside a cylinder, a technique still in use today. Newcomen's steam engine modified earlier pumps in two important ways: a closed cylinder replaced Savery's chamber, and the piston, instead of a vacuum, was used to create motion. Newcomen's design was generally significant in its capacity to produce motion to power a machine. The motion created allowed the engine to sustain its own movement; earlier steam-powered machines required that their water and steam valves be constantly monitored and manipulated. Newcomen's engine is called an atmospheric engine because its motion relies on atmospheric pressure rather than on counterweights or the force of steam itself. Steam approximately two pounds per square inch (psi) above atmospheric pressure was admitted to the underside of a piston. At a determined point in the cycle, a jet of water was injected to the same space to condense the steam, lowering the pressure underneath the piston to a near-vacuum. The atmospheric pressure in the open end of the cylinder then forced the piston back down, producing a power stroke. The replacement of brass cylinders with iron cylinders after 1724 was an additional step toward the higher-pressure steam engines to come.

In the 1720s, the German inventor Jacob Leupold designed a remarkably advanced engine that eliminated the condensation and vacuum steps of this process. Leupold's design called for two symmetrical cylinders that moved in opposition to create a continuous power source. The engine was apparently never built, however, probably because of limitations in the materials available and the current levels of craftsmanship.

The Scottish engineer James Watt who, contrary to popular belief, did not single-handedly invent the steam engine, still faced these technological limitations nearly fifty years later. Nonetheless, his design improvements of the 1770s and 1780s contributed most to the development of the modern steam engine. The first such design modification was to seal the engine's cylinder and install steam valves on both ends. Earlier engines had injected steam only on one side of the cylinder and employed counterweights or atmospheric pressure and vacuums to reset the piston in position. These earlier engines suffered in efficiency because of the heat dissipated during the procedure, which made reheating necessary at the beginning of each cycle. Watt found it difficult to seal the cylinders because those available were still being bored as they had been in Newcomen's time, and would not seal tightly enough for Watt's purpose. Watt tried to use jackets around his cylinders and a patented "stuffing box" to prevent steam from escaping when the piston rod moved through the cylinders, but these techniques proved inadequate.

To address this problem, Watt entered into a partnership in 1773 with businessman Matthew Boulton, who financed and organized a search for techniques to manufacture a well-sealed cylinder. John Wilkinson's boring machine, introduced in 1775, provided the solution. The refined design that resulted used one-third less fuel than a comparable Newcomen engine.

Watt also was responsible for an even more impressive innovation: attaching a flywheel to the engine. Flywheels accomplished two tasks. First, the inertia of a large flywheel allowed the engine to run more smoothly by creating a more constant load. Second, flywheels converted the conventional back-and-forth power stroke into a circular motion that could be adapted more readily to run machinery. Watt initially connected the engine and flywheel with a series of gears, but began using a crankshaft for this purpose when its earlier patent expired. Watt continued to experiment with, and improve upon, steam engine technology. In 1784, he patented a steam jet condenser and a parallel-motion, double-acting engine that admitted steam to both sides of the piston.

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. The American inventor Oliver Evans designed the first high-pressure, non-condensing engine by 1804. This engine forced steam into a cylinder at pressures of up to fifty psi. Evans's engine, which was stationary, operated at thirty revolutions per minute (rpm) and was used to power a marble-cutting saw. The British mechanical engineer and inventor Richard Trevithick was experimenting at this same time with similar engines. The high-pressure engines of both men retained the use of large cylindrical tanks of water, heated from beneath, to produce steam. The first practical alternative to these large boilers was introduced by John Stevens, a pioneer of the American steamboat. This new boiling system used rows of long, narrow pipes to carry water through flames. Water recirculated until it was converted to high-pressure steam, which then forced itself out of the pipes. The Stevens boiler system, however, frequently exploded when its unmonitored and uncontrolled pressure grew too great for the boiler and pipes to contain. Several mid-nineteenth century devices attempted to solve this problem though the use of stronger metals and improved seams--or to at least contain the damage of an explosion, as was the case with Isaiah Jenning's design for an outer casing for these boilers.

In this same period, a somewhat peripheral debate persisted over whether a cylinder should lie vertically or horizontally. Each option seemed to have its own advantages and applications. For example, boats were best served by a horizontal cylinder that ran the length of the vessel. In buildings such as mills, however, where floor space rather than a height limitation was at issue, vertical cylinders that often extended through several floors were employed. Neither position seemed more efficient, safer, or easier to access than the other. But this debate did trigger some new ideas. Some of these innovations involved resorting to alternated positions, as was the case with the oscillation or pendulum engine. In this engine, the cylinder swung back and forth, relieving stress in many parts of the engine and allowing for smoother operation. Alternate types of cylinders were also proposed, including the rotary cylinder, which eliminated altogether the flywheel and its interconnected moving parts. While such designs brought their own set of disadvantages--they often required more fuel or broke down more frequently--they continued the process of improvement and innovation on which technological advances depend.

In the 1860s and 1870s, George Corliss essentially perfected the steam engine. His large engines operated so smoothly that they could power textile mills in Scotland without breaking delicate threads, yet were large enough to power all the exhibits at the Machinery Hall during Philadelphia's 1876 Centennial Exhibition. Since the late nineteenth-century, gasoline-powered engines have largely replaced steam engines in the industrial market. Even today, however, steam turbines are used in the production of large quantities of energy for secondary distribution.

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