Pen y Bryn / Cloddfa’r Lôn water-driven pump system

Cadw's description

Summary description and reason for designation

Pen y Bryn / Cloddfa’r Lôn water driven pump system is located on the north slopes of the Nantlle Valley to the NE of Cloddfa’r Lôn Slate Quarry (CN302), E of Pen y Bryn Slate Quarry pit and N of Twll Balast. The scheduled area comprises two discrete areas retaining structural evidence of the ‘flat-rod’ system that once pumped the nearby pits of Twll Balast and Old Pen y Bryn.

The deep pit workings of the Nantlle Valley required continuous pumping to ensure the working areas remained accessible. Mechanised transmission systems were necessary in order to make use of waterpower without introducing further water into the quarry pits.

A water driven pump system was installed at Pen y Bryn / Cloddfa’r Lôn Quarry between 1836 and 1844 by a company based in Ottery St Mary, Devon, utilising technology typical of West Country mines. Waterwheels located at the surface powered a reciprocating system that utilised wrought iron rods under tension to transmit power to a series of pumps situated within the quarry pits. This system required the use of angle bobs that would have allowed changes in direction and smaller intermediate pillars to support the rods, as well as aqueducts and culverts to manage the water supply and drainage.

Pen y Bryn / Cloddfa’r Lôn water-driven pump comprises a system driven by two waterwheels located at the north end of the scheduled area (Area A). The eastern branch of the system transmitted power to Twll Balast and Twll Mawr via a number of supports heading downslope to the south. The western branch (Area B) transmitted the power via two substantial angle bob pillars to Old Pen y Bryn pit.

Area A includes two substantial waterwheel pits, 5 masonry angle-bob pillars and at least 10 smaller slate support pillars. Area B includes a substantial angle-bob pillar, with an adjacent support pillar, a deep vertical shaft, a cutting through the public footpath and slab lined drains. No obvious structural remains survive in the space between areas A and B although a drain is illustrated here on the Ordnance Survey 1st edition map (1889).

Most of the iron and timber components of the system have been removed but the structural elements preserve the course of the flat rod system. The relict wheel pits, rubble-built angle-bob towers and smaller slate support pillars survive as illustrated on the Ordnance Survey 1st edition map (1889). A number of wrought iron rods survive in the surrounding area, some having been reused in fencing.

The monument is of national importance for its potential to enhance our understanding of the slate quarrying industry, specifically technological innovations associated with water management. The Pen y Bryn / Cloddfa’r Lôn water-driven pump system was the longest such system in the slate industry of North Wales and remains the best preserved and most coherent example.

The scheduled area includes the remains described and an area around them in which further remains might be expected to survive. Area A is an irregular polygon c. 200m N-S by c.30m transversely and centred on NGR 250418, 353493. Area B is an irregular polygon measuring c.65m E-W by c.35m transversely centred on NGR 250301, 353449.