Wikipedia entry for the Cornish Beam Engine
A Cornish engine is a type of steam engine developed in Cornwall, England, mainly for pumping water from a mine. It is a form of beam engine that uses steam at a higher pressure than the earlier engines designed by James Watt. The engines were also used for powering man engines to assist the underground miners' journeys to and from their working levels, for winching materials into and out of the mine and for powering the ore stamping machinery.
The main characteristics of Cornish engines were: 1) the use of medium pressure steam (up to 50 psi), expansively, and 2) condensing the low pressure steam after expansion. Other characteristics included insulation of steam lines and the cylinder, and steam jacketing the cylinder, both of which had previously been used by Watt.
A Cornish engine pumps by a falling weight that is lifted by the engine. Few remain in their original locations, the majority having been scrapped when their related industrial firm closed.
The Cornish engine developed irregular power throughout the cycle, completely pausing at one point while having rapid motion on the down stroke, making it unsuitable for rotary motion and most industrial applications.