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]
Cornwall has long had tin, copper and other metal ore mines, but if mining is to take place at greater depths, a means to dewater the mine must be found. Lifting the weight of water up from the depths requires great amounts of work input. This energy may be weakly supplied by horse power or a waterwheel to operate pumps, but horses have limited power and waterwheels need a suitable stream of water. Accordingly, the innovation of coal-fired steam power to work pumps was more versatile and effective to the mining industry than primitive means.
The mine Wheal Vor had one of the earliest Newcomen engines (in-cylinder condensing engines, utilising sub-atmospheric 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 (43 kg)) of coal. Early Watt engines had a duty of 20 million, and later ones over 30 million. [2]
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 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):
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 ]
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 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. A test was carried out between a Trevithick type single-cylinder engine and a Woolf compound engine at Wheal Alfred in 1825, when both achieved a duty of slightly more than 40 million. [5]
The next improvement was achieved in the late 1820s by Samuel Grose, who decreased the heat loss by insulating the pipes, cylinders, and boilers of the engines, improving the duty to more than 60 million at Wheal Hope and later to almost 80 million at Wheal Towan. Nevertheless, the best duty was usually a short-lived achievement due to general deterioration of machinery, leaks from boilers, and the deterioration of boiler plates (meaning that pressure had to be reduced). [5]
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 Cornish stamps and whims, but generally came slightly later. In both cases the best duty was lower than for pumping engines, particularly so for whim engines, whose work was discontinuous. [2]
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 East London Waterworks in 1838, and compared to a Watt engine with favourable results, because the price of coal in London was even higher than in Cornwall. However, in the main textile manufacturing areas, such as Manchester and Leeds, the coal price was too low to make replacement economic. Only in the late 1830s did textile manufacturers begin moving to high-pressure engines, usually by adding a high-pressure cylinder, forming a compound engine, rather than following the usual Cornish practice. [2]
Several Cornish engines are preserved in England. The London Museum of Water & Steam has the largest collection of Cornish engines in the world. At Crofton Pumping Station, in Wiltshire are two Cornish engines, one of which (the 1812 Boulton and Watt) is the "oldest working beam engine in the world still in its original engine house and capable of actually doing the job for which it was installed", that of pumping water to the summit pound of the Kennet and Avon Canal. [6] Two examples also survive at the Cornish Mines and Engines museum on the site of East Pool mine near the town of Pool, Cornwall.
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 Cruquius pumping station in the Netherlands contains a Cornish engine with the largest diameter cylinder ever built for a Cornish engine, at 3.5 metres (140 inches) diameter. The engine, which was built by Harvey & Co in Hayle, Cornwall, has eight beams connected to the one cylinder, each beam driving a single pump. [8] The engine was restored to working order between 1985 and 2000, although it is now operated by an oil-filled hydraulic system, since restoration to steam operation was not viable. [9]
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]
A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be transformed, by a connecting rod and crank, into rotational force for work. The term "steam engine" is most commonly applied to reciprocating engines as just described, although some authorities have also referred to the steam turbine and devices such as Hero's aeolipile as "steam engines". The essential feature of steam engines is that they are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants, such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.
Thomas Newcomen was an English inventor who created the atmospheric engine, the first practical fuel-burning engine in 1712. He was an ironmonger by trade and a Baptist lay preacher by calling.
Thomas Savery was an English inventor and engineer. He invented the first commercially used steam-powered device, a steam pump which is often referred to as the "Savery engine". Savery's steam pump was a revolutionary method of pumping water, which improved mine drainage and made widespread public water supply practicable.
The atmospheric engine was invented by Thomas Newcomen in 1712, and is often referred to as the Newcomen fire engine or simply as a Newcomen engine. The engine was operated by condensing steam drawn into the cylinder, thereby creating a partial vacuum which allowed the atmospheric pressure to push the piston into the cylinder. It was historically significant as the first practical device to harness steam to produce mechanical work. Newcomen engines were used throughout Britain and Europe, principally to pump water out of mines. Hundreds were constructed throughout the 18th century.
The Watt steam engine design became synonymous with steam engines, and it was many years before significantly new designs began to replace the basic Watt design.
Richard Trevithick was a British inventor and mining engineer. The son of a mining captain, and born in the mining heartland of Cornwall, Trevithick was immersed in mining and engineering from an early age. He was an early pioneer of steam-powered road and rail transport, and his most significant contributions were the development of the first high-pressure steam engine and the first working railway steam locomotive. The world's first locomotive-hauled railway journey took place on 21 February 1804, when Trevithick's unnamed steam locomotive hauled a train along the tramway of the Penydarren Ironworks, in Merthyr Tydfil, Wales.
Stationary steam engines are fixed steam engines used for pumping or driving mills and factories, and for power generation. They are distinct from locomotive engines used on railways, traction engines for heavy steam haulage on roads, steam cars, agricultural engines used for ploughing or threshing, marine engines, and the steam turbines used as the mechanism of power generation for most nuclear power plants.
Steam power developed slowly over a period of several hundred years, progressing through expensive and fairly limited devices in the early 17th century, to useful pumps for mining in 1700, and then to Watt's improved steam engine designs in the late 18th century. It is these later designs, introduced just when the need for practical power was growing due to the Industrial Revolution, that truly made steam power commonplace.
A compound steam engine unit is a type of steam engine where steam is expanded in two or more stages. A typical arrangement for a compound engine is that the steam is first expanded in a high-pressure (HP) cylinder, then having given up heat and losing pressure, it exhausts directly into one or more larger-volume low-pressure (LP) cylinders. Multiple-expansion engines employ additional cylinders, of progressively lower pressure, to extract further energy from the steam.
Improvements to the steam engine were some of the most important technologies of the Industrial Revolution, although steam did not replace water power in importance in Britain until after the Industrial Revolution. From Englishman Thomas Newcomen's atmospheric engine, of 1712, through major developments by Scottish inventor and mechanical engineer James Watt, the steam engine began to be used in many industrial settings, not just in mining, where the first engines had been used to pump water from deep workings. Early mills had run successfully with water power, but by using a steam engine a factory could be located anywhere, not just close to a water source. Water power varied with the seasons and was not always available.
A beam engine is a type of steam engine where a pivoted overhead beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used by Thomas Newcomen around 1705 to remove water from mines in Cornwall. The efficiency of the engines was improved by engineers including James Watt, who added a separate condenser; Jonathan Hornblower and Arthur Woolf, who compounded the cylinders; and William McNaught, who devised a method of compounding an existing engine. Beam engines were first used to pump water out of mines or into canals but could be used to pump water to supplement the flow for a waterwheel powering a mill.
Lean's Engine Reporter was founded in 1810 to publicize the performances of different Cornish engines used for mine pumping in Cornwall. The first Reporter of Duty was Joel Lean. The Reporter, published monthly, gave, for each engine and its pumps, the number of strokes, and the amount of coal used. From this, and sizes of the pumps, the engine duty was found: this was the number of pounds of water raised one foot by a bushel of coal. Between 1810 and 1840 this reporting, and competition between engineers, raised the duty from around 20 million to 90 million pounds, a much higher efficiency than found in engines elsewhere at the same time. The improvements were an increase in the steam pressure used, full expansion to low pressure, and insulation to avoid heat loss.
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines-
Arthur Woolf was a Cornish engineer, most famous for inventing a high-pressure compound steam engine. In this way he made an outstanding contribution to the development and perfection of the Cornish engine.
The first recorded rudimentary steam engine was the aeolipile mentioned by Vitruvius between 30 and 15 BC and, described by Heron of Alexandria in 1st-century Roman Egypt. Several steam-powered devices were later experimented with or proposed, such as Taqi al-Din's steam jack, a steam turbine in 16th-century Ottoman Egypt, and Thomas Savery's steam pump in 17th-century England. In 1712, Thomas Newcomen's atmospheric engine became the first commercially successful engine using the principle of the piston and cylinder, which was the fundamental type of steam engine used until the early 20th century. The steam engine was used to pump water out of coal mines.
Old Bess is an early beam engine built by the partnership of Boulton and Watt. The engine was constructed in 1777 and worked until 1848.
A cataract was a speed governing device used for early single-acting beam engines, particularly atmospheric engines and Cornish engines. It was a kind of water clock.
The Newcomen Memorial Engine is a preserved beam engine in Dartmouth, Devon. It was preserved as a memorial to Thomas Newcomen, inventor of the beam engine, who was born in Dartmouth.
Nicholas Trestrail was a British mining engineer in Redruth, Cornwall, England. He was the designer of the Harvey's Engine, a Cornish beam engine initially used as a pumping engine as of 1892 in the Carn Brea mine and from 1924 till 28 September 1954 in the East Pool mine.
Valve gear opens and closes valves in the correct order. In rotating engines valve timings can be driven by eccentrics or cranks, but in non-rotative beam engines these options are not available. In the Cornish engine valves are driven either manually or through ‘plug rods’ and tappets driven from the beam. This permits the insertions of delays at various points in the cycle, allowing a Cornish Engine to vary from one stroke in ten minutes, to ten or more strokes in one minute, but also leads to some less familiar components when compared with rotative engines.
