Cornish 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 on-site ore stamping machinery.[1]
Background: The steam engine in Cornwall
The mine
Cornish cycle
The Cornish cycle operates as follows.[3]
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 pressurized steam inlet valve and low-pressure steam exhaust valves are opened. Pressurized steam from the boiler enters the top part of the cylinder above the piston, pushing it down, and the steam below the piston is drawn into the condenser, creating a vacuum below the piston. The pressure difference between the steam at boiler pressure above the piston and the vacuum below it drives the piston down.
- Part way down the stroke, the pressurized steam inlet valve is closed. The steam above the piston then expands through the rest of the stroke, while the low-pressure steam on the other side (bottom) of the piston continues to be drawn into the condenser, thereby maintaining the partial vacuum in that part of the cylinder.
- At the bottom of the stroke, the exhaust valve to the condenser is closed and the equilibrium valve is opened. The weight of the pump equipment down in the mine, transferred by the walking beam, draws the piston up, and as the piston comes up, steam is transferred through the equilibrium pipe from above the piston to the bottom of the cylinder below the piston.
- When the piston reaches the top of the cylinder, the cycle is ready to repeat.
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.
The engine is single-acting, and the steam piston is pulled up by the weight of the pump piston and rodding. Steam may be supplied at a pressure of up to 50 pounds per square inch (340 kPa).
Real photos showing the components of the schematic design (East Pool mine Tailer's shaft Harvey's Engine):
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Steam boilers
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Main steam cylinder (A)
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Control steam
cylinders (G-H) -
Pump lever (D)
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Engine house and pump piston (E)
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Sacrifice block in the engine house of Taylor's Shaft East Pool mine
Characteristics
The principal advantage of the Cornish engine was its increased efficiency, accomplished by making more economical use of higher-pressure steam. At the time, improvements in efficiency were important in Cornwall because of the high cost of coal; there are no coal fields in Cornwall and all the coal used had to be brought in from outside the county.[citation needed]
Increasing the boiler pressure above the very low, virtually atmospheric pressure steam used by James Watt was an essential element of the improvement in efficiency of the Cornish engine. However, simply increasing the boiler pressure would have made an engine more powerful without increasing its efficiency. The key advance was allowing the steam to expand in the cylinder. 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.[citation needed]
In a Watt engine, steam is admitted throughout the piston's power stroke. At the end of the stroke, the steam is exhausted, and any remaining energy is wasted in the condenser, where the steam is cooled back to water.[citation needed]
In a Cornish engine, by contrast, the intake valve is shut off midway through the power stroke, allowing the steam already in that part of the cylinder to expand through the rest of the stroke to a lower pressure. 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.[citation needed]
Other characteristics include insulation of steam lines and the cylinder, and steam jacketing the cylinder, both of which had previously been used by Watt.[4]
Few Cornish engines remain in their original locations, the majority having been scrapped when their related industrial firm closed.[1]
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.[4] This also requires some unusual valve gear, see Cornish engine valve gear.[citation needed]
Development of the Cornish engine
The Cornish engine depended on the use of steam pressure above atmospheric pressure, as devised by Richard Trevithick in the 19th century. Trevithick's early "puffer" engines discharged steam into the atmosphere. This differed from the Watt steam engine, which moved the condensing steam from the cylinder to a condenser separate from the cylinder; hence Watt's engine depended on the creation of a vacuum when the steam was condensed. Trevithick's later engines (in the 1810s) combined the two principles, starting with high-pressure steam which was then passed to the other side of the piston, where it condensed and there it acted as a sub-atmospheric pressure engine. In a parallel development Arthur Woolf developed the compound steam engine, in which the steam expanded in two cylinders successively, each of which were at pressures above atmospheric.[2]
When Trevithick left for South America in 1816 he passed his patent right of his latest invention to
The next improvement was achieved in the late 1820s by
Minor improvements increased the duty somewhat, but the engine seems to have reached its practical limits by the mid-1840s. With pressures of up to 50 pounds per square inch (340 kPa), the forces are likely to have caused machinery breakages. The same improvements in duty occurred in engines operating
The impetus for the improvement of the steam engine came from Cornwall due to the high price of coal there, but both capital and maintenance costs were higher than a Watt steam engine. This long delayed the installation of Cornish engines outside Cornwall. A secondhand Cornish engine was installed at
Preserved Cornish engines
Several Cornish engines are preserved in England. The
Another example is at Poldark Mine at Trenear, Cornwall – a Harvey of Hayle Cornish Beam Engine from about 1840–1850, originally employed at Bunny Tin Mine and later at Greensplat China Clay Pit, both near St Austell. It no longer works as a steam engine but is instead moved by a hydraulic mechanism. In use at Greensplat until 1959, it is the last Cornish engine to have worked commercially in Cornwall. It was moved to Poldark in 1972.[7]
The
The Cornish Engines Preservation Committee, an early industrial archaeology organisation, was formed in 1935 to preserve the Levant winding engine. The Committee was later re-named for Richard Trevithick. They acquired another winding engine and two pumping engines.[10] They publish a newsletter, a journal and many books on Cornish engines, the mining industry, engineers, and other industrial archaeological topics.[11][12]
See also
- Beam engine
- Mining in Devon and Cornwall
- Stationary steam engine
- Lean's Engine Reporter
- Cataract (beam engine)
References
- ^ a b Barton, D. B. (1966). The Cornish Beam Engine (New ed.). Truro: D. Bradford Barton.
- ^ S2CID 154050461.
- ^ "The Cornish Cycle". Archived from the original on 28 July 2015. Retrieved 5 January 2015.
- ^ a b Hunter, Louis C. (1985). A History of Industrial Power in the United States, 1730-1930, Vol. 2: Steam Power. Charlottesville: University Press of Virginia.
- ^ S2CID 56298553.
- ^ "Crofton". Archived from the original on 6 August 2011.
- ^ Fyfield-Shayler (1972). The Making of Wendron. Graphmitre Ltd archive.
- ^ "Construction". Cruquius Museum. Archived from the original on 19 July 2011. Retrieved 3 August 2009.
- ^ "Hydraulic". Cruquius Museum. Archived from the original on 19 July 2011. Retrieved 3 August 2009.
- ^ Trevithick Society. Archived 8 March 2016 at the Wayback Machine Open Lectures and Talks. Retrieved 22 September 2012.
- ^ Trevithick Society. The Journal of the Trevithick Society, Issues 6-10. Trevithick Society, 1978.
- ^ Trevithick Society. Archived 2 January 2013 at archive.today Cornish Miner - Books on Cornwall. Retrieved 22 September 2012.
External links
- Cornish beam engine animation
- Cruquius pumping station (includes mechanical details, simulations, technical drawings, etc.)
- Cornish engine history, context
- "The Cornish Cycle" on YouTube