Last of the giants
E&T looks at the life and times of the Cornish beam engine - a magnificent example of Victorian engineering that helped transform 19th century Cornwall into the mining capital of the world.
Viewed on a grey winter's day, the red brick and granite buildings of the East Pool Mine near Redruth in Cornwall have the melancholy charm befitting an industrial leviathan, incongruously beached alongside a supermarket car park. The immediate environs may be a little unprepossessing, but this grey-red assortment of buildings is home to Cornwall's largest surviving Cornish beam engine - an iconic piece of industrial design that, during the first half of the 19th century, transformed Cornwall from a sparsely-populated rural outpost into the world's most important centre for the deep mining of tin and copper.
Cornish beam engines came in a number of standard sizes, and the engine at Taylor's Shaft at East Pool was a top-of-the-range model with a 90in diameter cylinder. Nothing can prepare you for the visual impact of something so huge. You step through the side door of the engine house, and the only thing you seem to see is this great cylinder, encased in wood, bound with brass hoops and resting on its massive cast iron base.
The overwhelming impression of size and power continues as you climb up to the second and third floors. The second floor reveals the top of the cylinder - elegant in its Victorian cast iron and brass work - and the piston rod with its ten-foot stroke.
Finally, the top floor of the engine house is filled with the 52t, 33ft beam. Pivoted on its fulcrum, resting on padstones set in a granite wall 80in thick, this immense structure connects the top of the piston rod to the timber and iron pumping rod that once reached down 1,700ft into the mine shaft.
Every 12 seconds, the descending weight of the pump rod drove a series of pump rams to lift 92 gallons of water, moved upwards via a series of cisterns positioned at 240ft intervals along the length of the shaft.
The Cornish engine was essentially a development of the Watt steam engine, adapted to use high-pressure steam. With the ending of the Watt-Boulton patent in 1800, Cornish engineers were free to introduce a range of design innovations.
Foremost among the engineers was Richard Trevithick, the son of the manager of the Wheal Chance copper mine, near Camborne. The Watt engine, and its predecessor, the Newcomen engine, used low-pressure steam, just above atmospheric pressure, supplied by boilers that were little more than giant kettles. The technology was crude but safe, and leaks could be repaired with a brick and a clod of earth.
Trevithick was an advocate of the use of high-pressure steam. He called it "strong steam" and he invented a novel boiler, appropriately known as the Cornish boiler, to produce it. Comprising a wrought iron cylinder with a large fire tube through its centre, Trevithick's new boiler could easily generate steam at pressures of around 50psi and above. As he is reported to have said: "My predecessors put their boiler into the fire, I have put my fire into the boiler." The genesis of the Cornish engine can be traced to 1812, when Trevithick attached a Cornish boiler to a Watt engine at the Wheal Prosper mine.
Trevithick's intuitive belief in the virtues of strong steam were well founded. Higher pressures, and hence higher temperatures, implied greater efficiency, and in its developed state the Cornish engine had a thermal efficiency of around 8 per cent.
The five great boilers of the East Pool mine have long since gone for scrap, but the abundant supplies of 50psi steam they provided over their long working life were absolutely crucial to the ability of this engine to lift some 460 gallons of water a minute, day in and day out, for decades on end.
A working life
The Victorians built to last, and the East Pool engine is no exception to this rule. It was commissioned in 1891, and started its working life a year later at the nearby Carn Brea Mine. In 1913, Carn Brea failed, and the engine stood idle for the next decade until it was bought by the East Pool and Agar mine to pump the recently sunk Taylor shaft - named after the mine's manager. It was housed in a brand new engine house - almost certainly the last to be erected in Cornwall - and re-commenced pumping in 1925.
East Pool and Agar mine finally closed in October 1945 - the Second World War had helped extend its working life. Thereafter, the East Pool engine was used to pump the workings of the adjacent South Crofty mine. This magnificent machine was shut down at 11.30am on 28 September 1955. There were, it's said, tear-filled eyes among the engine room staff as the great pump finally came to rest.
The Cornish mining industry went into decline from 1870 onwards. Competition from Malaya and Bolivia destroyed the commercial viability of Cornish tin mines, while the US dealt a similar blow to the copper mines. At the industry's peak, there were some 650 beam engines operating in Cornwall.
By the mid-1920s, this figure had fallen to around 20. The continued existence of the East Pool engine, and the three other Cornish engines still preserved in situ, is attributable to the work of the Cornish Engine Preservation Society (founded in 1943, and re-named the Trevithick Society in 1971).
Responsibility for the continued preservation of the Society's Cornish engines was transferred to the National Trust in 1967.