Humanities › History & Culture How Do Steam Engines Work? They were the first source of mechanical power invented by mankind Share Flipboard Email Print Donning Kindersley / Getty Images History & Culture Inventions Famous Inventions Famous Inventors Patents & Trademarks Invention Timelines Computers & The Internet American History African American History African History Ancient History and Culture Asian History European History Genealogy Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By Mary Bellis Inventions Expert Mary Bellis covered inventions and inventors for ThoughtCo for 18 years. She is known for her independent films and documentaries, including one about Alexander Graham Bell. our editorial process Mary Bellis Updated August 16, 2019 Heat water to its boiling point and it changes from being a liquid to become the gas or water vapor we know as steam. When water becomes steam its volume increases about 1,600 times, that expansion is full of energy. An engine is a machine that converts energy into mechanical force or motion that can turn pistons and wheels. The purpose of an engine is to provide power, a steam engine provides mechanical power by using the energy of steam. Steam engines were the first successful engines invented and were the driving force behind the industrial revolution. They have been used to power the first trains, ships, factories, and even cars. And while steam engines were definitely important in the past, they also now have a new future in supplying us with power with geothermal energy sources. How Steam Engines Work To understand a basic steam engine, let's take the example of the steam engine found in an old steam locomotive like the one depicted. The basic parts of the steam engine in a locomotive would be a boiler, slide valve, cylinder, steam reservoir, piston, and a drive wheel. In the boiler, there would be a firebox where coal would be shoveled into. The coal would be kept burning at a very high temperature and used to heat the boiler to boil water producing high-pressure steam. The high-pressure steam expands and exits the boiler via steam pipes into the steam reservoir. The steam is then controlled by a slide valve to move into a cylinder to push the piston. The pressure of the steam energy pushing the piston turns the drive wheel in a circle, creating motion for the locomotive. History of Steam Engines Humans have been aware of the power of steam for centuries. Greek engineer, Hero of Alexandria (circa 100 AD), experimented with steam and invented the aeolipile, the first but very crude steam engine. The aeolipile was a metal sphere mounted on top of a boiling water kettle. The steam traveled through pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere released the steam, which gave a thrust to the sphere that caused it to rotate. However, Hero never realized the potential of the aeolipile, and centuries were to pass before a practical steam engine would be invented. In 1698, English engineer, Thomas Savery patented the first crude steam engine. Savery used his invention to pump water out of a coal mine. In 1712, English engineer and blacksmith, Thomas Newcomen invented the atmospheric steam engine. The purpose of Newcomen's steam engine was also to remove water from mines. In 1765, a Scottish engineer, James Watt began studying Thomas Newcomen's steam engine and invented an improved version. It was Watt's engine that was the first to have a rotary motion. James Watt's design was the one that succeeded and the use of steam engines became widespread. Steam engines' had a profound effect on the history of transportation. By the late 1700s, inventors realized that steam engines could power boats and the first commercially successful steamship was invented by George Stephenson. After 1900, gasoline and diesel internal combustion engines began replacing the steam piston engines. However, steam engines have reappeared in the last twenty years. Steam Engines Today It may be surprising to know that 95 percent of nuclear power plants use steam engines to generate power. Yes, the radioactive fuel rods in a nuclear power plant are used just like coal in a steam locomotive to boil water and create steam energy. However, the disposal of spent radioactive fuel rods, the vulnerability of the nuclear power plants to earthquakes and other issues leaves the public and the environment at great risk. Geothermal power is power generated using steam produced by heat emanating from the molten core of the earth. Geothermal power plants are relatively green technology. Kaldara Green Energy, a Norwegian/Icelandic manufacturer of geothermal electrical power production equipment, has been the major innovator in the field. Solar thermal power plants can also use steam turbines to generate their power.