Once underground mining really got under way in Cornwall around 1500 the major issue rapidly became drainage: how to get water out of the mines. Where possible an adit could be used to simply allow the water to drain naturally, but as time passed and mines got deeper, natural drainage was not always possible, and a means had to be found to bring water up to adit level. A variety of mechanisms were used over the years including water wheels, rag and chain pumps, barrels raised by horse whims or bucket and windlass. Levant was still draining its Wheal Unity section using a horse whim and barrels in the mid 19th century and in 1821 Joseph Carne described Levant as being such a dry mine that water was taken care of by two men with a windlass and bucket.
With the appearance of the Newcomen atmospheric engine in the early 18th century it became clear that the future lay with coal powered steam pumps, and for Cornwall the problem was always going to lie in the cost of coal. Brought from south Wales by ship and delivered to ports such as Hayle, Penzance, the quays of the Fal and Portreath and then carried overland by pack animals the cost of coal became a major determinant in the profitability of mines. It was the high cost of coal which led mine owners and their engineers to look for efficiency savings and resulted in Cornwall's pre-eminent role in the evolution of the steam engine.
Trevithick is the engineer most associated with this effort but his inventive genius was not restricted to steam. He also took an idea which had been around for nearly 200 years, the water pressure engine, and developed it into a reliable pumping device. (He wasn't the first to do this, a water pressure engine had been erected at Coalcleugh in the north Pennines in 1765) The great thing about the water pressure engine was that it did not need coal, what it needed was a significant head of water, the power of which, falling in a pipe, was sufficient to move a piston in a cylinder in much the same way as was otherwise achieved using steam. Water wasn't free, in fact water rights and the rights to transport water could be quite costly but not in the same league as coal.
Trevithick erected his first water pressure engines at Wheal Druid and Roskear just before 1800, the Roskear engine working successfully for 17 years before being repaired and re-built. One of the strengths of these engines was that they could function more or less without maintenance for years at a time. On the face of it not everywhere was suitable for a water pressure engine because the main requirement was the large head of water. In fact, many mines were suitable as they could employ water falling down a shaft as the head. A prospectus for Wheal Down in the Royal Cornwall Gazette on the 17th February 1821 stresses the advantage of the site:
“A large stream of water passes along the …….adit which in its perpendicular descent to the County Adit of 14 fathoms may be applied by means of a pressure engine to drain the mine to a considerable depth, without the expensive application of a steam engine.”
Wheal Cock Engine Shaft, the shaft is situated behind the wall which was built in te late 19th century. From the opening at the bottom of the wall it is about 150 feet down to sea-level and the location of the adit. (photo Ted Mole)
It's not always easy to identify when newspapers are talking about water pressure engines as opposed to other water power devices eg water wheels, but advertisements for mines and mining equipment are, nevertheless, a key source if information. On 5th August 1836 The West Briton carried an advertisement for the sale of Wheal Cock Mine, St Just, which was drained by a 10” water pressure engine working with a 40 fathom head of water. The Royal Cornwall Gazette carried an advertisement dated 2nd August 1836 for a sale of mining materials from Wheal Cock which included two pressure engines. The West Briton description suggest that this is definitely a true water pressure engine, the 40 fathom head (240 feet) being easily accommodated by the 300 feet high cliffs. The water pressure engine is probably the successor the the “water engine” which is shown on the Charles Moody's map of Wheal Cock and Botallack drawn in 1782. The map shows the “water engine”, probably a water wheel, positioned where Wheal Cock engine shaft is located and this shaft is the likely location of the 1836 water pressure engine. The pump itself would have been located at adit level, just above the sea while head of water would have been taken down the shaft in pipes supplied from the extensive system of leats and ponds on and above the cliffs.
The mines of the St Just district have had a reputation for being behind the times and technically conservative, a reputation probably deriving as much as anything from the fact that Levant was still using a man engine in 1919 and had been through several periods of sustained under investment, as in the 1860s, when old machinery was worked into the ground. But it may also derive from the fact that there is no evidence of steam engines in St Just before the first decade of the 19th century. St Just mines continued to use water power on a significant scale, as at Wheal Cock. This was not obsolete technology however so much as appropriate technology. Wheal Cock was an ideal location for for the innovative water pressure engine which completely avoided the fuel and maintenance costs associated with steam. In isolated St Just coal was more than usually expensive because it had to be brought 7 miles overland by mule train from the port of Penzance so it made sense to use what we would now call renewable energy.