Published on Jan 19, 2016
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.
Earlier engines depended on atmospheric pressure to push the piston into the cylinder, where sudden cooling of its steam content created a vacuum. 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.
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