\Steam" en"gine\
An engine moved by steam.
Note: In its most common forms its essential parts are a
      piston, a cylinder, and a valve gear. The piston works
      in the cylinder, to which steam is admitted by the
      action of the valve gear, and communicates motion to
      the machinery to be actuated. Steam engines are thus
      classified: 1. According to the wat the steam is used
      or applied, as condencing, noncondencing, compound,
      double-acting, single-acting, triple-expansion, etc. 2.
      According to the motion of the piston, as
      reciprocating, rotary, etc. 3. According to the motion
      imparted by the engine, as rotative and nonrotative. 4.
      According to the arrangement of the engine, as
      stationary, portable, and semiportable engines, beam
      engine, oscillating engine, direct-acting and
      back-acting engines, etc. 5. According to their uses,
      as portable, marine, locomotive, pumping, blowing,
      winding, and stationary engines. Locomotive and
      portable engines are usually high-pressure,
      noncondencing, rotative, and direct-acting. Marine
      engines are high or low pressure, rotative, and
      generally condencing, double-acting, and compound.
      Paddle engines are generally beam, side?lever,
      oscillating, or direct-acting. Screw engines are
      generally direct-acting, back-acting, or oscillating.
      Stationary engines belong to various classes, but are
      generally rotative. A horizontal or inclined stationary
      steam engine is called a left-hand or a right-hand
      engine when the crank shaft and driving pulley are on
      the left-hand side, or the right-hand side,
      respectively, or the engine, to a person looking at
      them from the cylinder, and is said to run forward or
      backward when the crank traverses the upward half, or
      lower half, respectively, of its path, while the piston
      rod makes its stroke outward from the cylinder. A
      marine engine, or the engine of a locomotive, is said
      to run forward when its motion is such as would propel
      the vessel or the locomotive forward. Steam engines are
      further classified as double-cylinder, disk,
      semicylinder, trunk engines, etc. Machines, such as
      cranes, hammers, etc., of which the steam engine forms
      a part, are called steam cranes, steam hammers, etc.
      See Illustration in Appendix.
{Back-acting}, or {Back-action}, {steam engine}, a steam
   engine in which the motion is transmitted backward from
   the crosshead to a crank which is between the crosshead
   and the cylinder, or beyond the cylinder.
{Portable steam engine}, a steam engine combined with, and
   attached to, a boiler which is mounted on wheels so as to
   admit of easy transportation; -- used for driving
   machinery in the field, as trashing machines, draining
   pumps, etc.
{Semiportable steam engine}, a steam engine combined with,
   and attached to, a steam boiler, but not mounted on
   wheels.