Stēam'-ēn'gine, n.

(-ēn'jĭn), n. An engine moved by steam.

It consists principally of a piston receiving motion in a cylinder to which steam is admitted by the valve-gear, and communicating motion to the valve-gear and to the machinery to be actuated. Steam-engines are classified as, (1.) Condensing and non-condensing, which are generally low-pressure and high-pressure respectively. (2.) According to the action of the steam, as reciprocating (including single-acting and double-acting) and rotatory. See ROTATORY. (3.) According to the motion derived, as rotative and non-rotative. (4.) According to the arrangement of the engine, as beam-engine (of which the side-lever engine is a modification), oscillating engine (of which the vibrating engine is a modification), direct-acting and back-acting engines. The two latter classes may be horizontal, inclined, or vertical. Vertical engines are conveniently classified as steam-hammer engines, having the cylinder at the top, and steeple engines, having the cylinder at the bottom. (5.) According to their uses, as portable, marine, locomotive, pumping, blowing, winding, and stationary engines, the latter term referring to factory engines, &c., and not technically to pumping or blowing engines. Pumping engines are stationary (the smaller classes are called steam-pumps) or portable (steam fire-engines), and are generally non-rotative. The Cornish engine, the best type of the class, is a single-acting, non-rotative beam-engine. Locomotive and portable engines are usually high-pressure, non-condensing, rotative, and direct-acting. Marine engines are high or low pressure, rotative, and generally condensing and double-acting. 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. Steam-engines are further classified as double-cylinder, disk, semi-cylinder, trunk engines, and the like. Machines of which the steam-engine forms a part, are called steam-cranes, steam-hammers, and the like. See VALVE-GEAR and SLIDE-VALVE.