The Pumping Engine House at Dorothea Slate Quarry, Talysarn, Nantlle Valley, north Wales, UK.
The Dorothea Quarry specialised in the production of blue and purple slates, mostly for roofing. Slate is a metamorphosed shale and that in Snowdonia is of Ordovician age. The quarry officially opened in 1829 though illegal quarrying in and around Nantlle had been active throughout the eighteenth century. Further investment was made in 1835 but production did not really get underway until the building boom of the latter nineteenth century.
The Dorothea Quarry is five hundred feet deep and the last four hundred are in water. Around 1900 the company experimented with electric pumps to keep the quarry dewatered but was dissatisfied with them. Accordingly, in 1906 they installed a Cornish engine by Holman Brothers of Camborne, said to be the last ever built.
The engine pumped ten gallons per second from five hundred feet working in a shaft of 465 feet depth. Its two coal-fired Lancashire boilers fed steam to a sixty-inch diameter single cylinder that rocked a cast-steel beam of twenty-three tons. The engine worked until 1951 when it was replaced by a sixty horse-power electric pump. It did brief duty in 1956.
The engine and its house remain intact though the pump assembly has decayed and the boilers have been vandalised by copper thieves.
The quarry closed in 1970
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