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.

Bibliography: 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.

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.