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Back-acting steam engine, 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 thrashing machines, draining pumps, etc. -- Semiportable steam engine, a steam engine combined with, and attached to, a steam boiler, but not mounted on wheels.