an installation that combines a steam boiler, a piston steam engine, and auxiliary equipment in a single unit.
Mobile (wheeled) steam power units have a steam boiler of the type used for locomotives; the rated power of the steam engine is 8.5-55.0 kilowatts (Kw), or 12–75 hp. Such units operate on saturated or superheated steam at a pressure of 1.0-1.2 mega-newtonsper sq m (MN/m2), or 10−12 kilograms-force per sq cm (kgf/cm), with exhaustion of steam to the atmosphere; they are mainly used in agriculture. Stationary units are used in small industrial enterprises, usually as the drive for electric power generators. The boilers of such units have a cylindrical firebox and a pull-out system of fire tubes. The pressure of the superheated steam is about 1.5 MN/m2 (15 kgf/cm2), and the rated power of the steam engines is 90–580 kW (125-800 hp). For enterprises using steam for industrial purposes (boiling, drying, or heating) the units are usually of the direct-heating type, with intermediate steam bleeding, or are constructed for a back pressure up to 0.35 MN/m2 (3.5 kgf/cm2). Various waste products (sawdust, chaff, chips, or husks) or locally available materials (wood or peat) are used as fuel. Among the advantages of steam power units are reliability, low requirements for quality of water and fuel, long service life, and simplicity of installation in the field. Their disadvantages include low efficiency and high metal consumption. In the USSR the manufacture of such installations ended in the 1960’s. They are being replaced by the more efficient electric motors and internal-combustion engines.