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. However, James Watt's steam engine, patented in 1769, provided the first practical solution. From the Greek inventor Heron of Alexandria to the Englishmen Thomas Newcomen and John Cawley, many persons contributed to the work of harnessing steam. 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. In a single-cylinder steam engine the exhaust steam is usually expelled directly into the atmosphere. Steam from the other inlet valve then pushes the piston back to its original position, and the cycle starts again. This steam then exits through an exhaust valve. Steam is admitted through one inlet valve, forcing the piston to move to the other end of the cylinder. The typical steam engine has an inlet valve at each end of the cylinder. A flywheel attached to the crankshaft makes the rotary motion smooth and steady. 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. Steam engines operate by having superheated steam force a piston to reciprocate, or move back and forth, in a cylinder. The force produced by the conversion is the basis of all steam engines. When water is converted into steam it expands, its volume increasing about 1,600 times. Steam engine, machine for converting heat energy into mechanical energy using steam as a medium, or working fluid.
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