Cornish Engine - Background: The Steam Engine in Cornwall

Background: The Steam Engine in Cornwall

Cornwall has long had mines for tin, copper and other metal ores, but if mining is to take place below adit (essentially, the level of an entrance which can both drain and ventilate the diggings), some means of draining water from the mine must be found . This may be done using horse power or a waterwheel to operate pumps, but horses have limited power and waterwheels need a suitable stream of water. Accordingly, the conversion of coal into power to work pumps was highly desirable to the mining industry.

Wheal Vor (mine) had one of the earliest Newcomen engines (in-cylinder condensing engines, utilizing sub-atmosperic pressure) before 1714, but Cornwall has no coalfield and coal imported from south Wales was expensive. The cost of fuel for pumping was thus a significant part of mining costs. Later, many of the more efficient early Watt engines (using an external condenser) were erected by Boulton and Watt in Cornwall. They charged the mine owners a royalty based on a share of the fuel saving. The fuel efficiency of an engine was measured by its "duty", expressed in the work (in foot-pounds) generated by a bushel (94 pounds) of coal. Early Watt engines had a duty of 20 million, and later ones over 30 million.