Cornish engine

Lifting the weight of water up from the depths requires great amounts of work input.

Accordingly, the innovation of coal-fired steam power to work pumps was more versatile and effective to the mining industry than primitive means.

The fuel efficiency of an engine was measured by its "duty", expressed in the work (in foot-pounds) generated by a bushel (94 pounds (43 kg)) of coal.

[2] The principal advantage of the Cornish engine was its increased efficiency, accomplished by making more economical use of higher-pressure steam.

While James Watt had conceived of the idea of allowing expansive working of steam—and included it in his 1782 patent, he realized that the low steam pressure of his application made the improvement in efficiency negligible, and so did not pursue it.

This results in the capture of a greater proportion of its energy, and less heat being lost to the condenser, than in a Watt engine.

[3] Few Cornish engines remain in their original locations, the majority having been scrapped when their related industrial firm closed.

[4] Starting from a condition during operation with the piston at the top of the cylinder, the cylinder below the piston full of steam from the previous stroke, the boiler at normal working pressure, and the condenser at normal working vacuum, The next stroke may occur immediately, or it may be delayed by a timing device such as a cataract, if it was not necessary for the engine to work at its maximum rate, reducing the rate of operation saved fuel.

Real photos showing the components of the schematic design (East Pool mine Tailer's shaft Harvey's Engine): The Cornish engine depended on the use of steam pressure above atmospheric pressure, as devised by Richard Trevithick in the 19th century.

[2] When Trevithick left for South America in 1816 he passed his patent right of his latest invention to William Sims, who built or adapted a number of engines, including one at Wheal Chance operating at 40 pounds per square inch (280 kPa) above atmospheric pressure, which achieved a duty of nearly 50 million, but its efficiency then fell back.

The same improvements in duty occurred in engines operating Cornish stamps and whims, but generally came slightly later.

In the main textile manufacturing areas, such as Manchester and Leeds, the coal price was too low to make replacement economic.

The London Museum of Water & Steam has the largest collection of Cornish engines in the world.