section_path: Components and accessories of steam engines/Motor units
section_name: Motor units
paragraph_text: Motor units
  
  In a steam engine, a piston or steam turbine or any other similar device for doing mechanical work takes a supply of steam at high pressure and temperature and gives out a supply of steam at lower pressure and temperature, using as much of the difference in steam energy as possible to do mechanical work.
  
  These "motor units" are often called 'steam engines' in their own right. Engines using compressed air or other gases differ from steam engines only in details that depend on the nature of the gas although compressed air has been used in steam engines without change.