Cuffley Industrial Heritage Society

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Pontcysyllte aqueduct

Started in 1795 and completed in 1805, it carries the canal high above the River Dee. Following the use of cast iron within masonry at Chirk, Telford built a prototype cast-iron trough aqueduct at Longdon on Tern in 1796. Although a much smaller and lower structure, it proved the principles, and allowed Telford to build the tall but light and slender Pontcysyllte.

The aqueduct is 1007 ft. long, and 121ft above the river at its highest point. The trough which is 11ft 9in wide, is carried on four arch ribs over each of the nineteen 44ft  6in spans between the masonry piers.

The embankment on the south end was one of the greatest earthworks of its time.

 Llanberis “Electric Mountain” visitor centre

The visitor centre has an excellent museum displaying three boats dredged out of the silt in the adjoining lakes. The “Peris Boat” has been dated by dendrochronology to 1547-1549.  At 6.3 metres long and 2.2 metres in the beam, it is thought to have been an early means of transporting goods and people across the upper lake Llyn Peris.

There are also an even earlier log boat (dated 1187-1205), and a late-18th century  flat-bottomed, keel-less vessel similar to a dory, of very similar size to the Peris boat

See Ref 2 for more details

The visitor centre also houses photographs of life in the quarry, and an art display


Dinorwig Pump-Storage Power Station

This is the largest pumped storage power station in the world.  It is in effect a means of storing energy.  It uses off-peak electricity from the “base-load” stations of the national grid to pump water from the lower lake, Llyn Peris, up to Marchlyn Mawr, and then allows it to fall back down through turbines to generate electricity when there is a peak demand. The six turbines work in reverse as pumps, on average for six hours at night, and then generate  for five hours each day with an average output of 1680 MW.  A load of up to 1320 MW can be picked up in ten seconds (especially useful in the TV commercial breaks when everyone puts the kettle on at once).

This system gives substantial efficiency gains to the overall electricity generation process. It allows the large thermal base load stations to run at their optimum output, rather than having to build additional ones for the peak, and running them below optimum in the off-peak.

All the machinery of this massive station are hidden in a huge caverns within Elidir mountain.  The main hall is 590 ft long, 80 ft wide and 197 ft high.

We will see the smaller prototype for this scheme at Tan-y-Grysiau when we visit Blaenau Ffestiniog tomorrow.

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2003 Page 4 of 7  Study tour case notes

The Welsh Slate Museum, Gilfach Ddu, Llanberis

The museum is housed in the workshop building of the Dinorwig Quarry where almost anything required to be manufactured for the quarry could be produced, and  is as though the quarrymen and engineers have just put down their tools and left.

Constructed in 1869-70 in the form of a quadrangle, it was originally powered by a huge water wheel (diagram below) which is hidden within the South wall of the building. The wheel is constructed entirely of iron and measures 50ft 5in diameter,  5ft 3in breast, and rests on a 12in diameter axle. It ceased to be used in 1925 when a  pelton wheel was commissioned.

The museum has much to offer:-

A multi-media presentation evoking the lives of the quarrymen.

Demonstrations of slate-splitting, brass-founding and blacksmithing.

· A fascinating tour of the workshops, iron and brass foundry, forges, locoshed and water-powered machinery which made the tools for winning the slate.

· A row of four quarrymen’s houses transhipped from Tanygrisiau and reassembled to recapture significant periods from the life of slate.


Afterwards we will have a demonstration of the restored Vivian incline.

Dinorwig Quarry, and the Padarn Railway

The quarry covered about 700 acres in two sections each with twenty galleries.

2004 Study tour case notes

C I H S Study trip notes