Everyone should visit Trefriw Woollen Mills. It's fascinating, educational, and even more importantly, free. This report is image heavy, and I make no apology for that. I do it because I care, and because it's what's best for you.
Originally a Pandy (fulling mill), it was situated on the fast running River Crafnant in order to use the water to drive the waterwheels and to wash the wool. The earliest fulling mill in Trefriw dates back to the 15th century (fulling is the process that cleans and thickens the wool). A water-powered fulling mill replaced the previous cottage-industry type process in 1820, but it took Thomas Williams' purchase of the mill in 1859 to see any serious development of the industry. The original buildings are still standing behind the modern 1970s premises:
Here's what the wheel looked like in the mid-19th century:
Fulling mills, from medieval times onwards, were often water powered. The cloth was beaten with wooden hammers, known as fulling stocks. There were two kinds of fulling stocks, but in both cases the machinery was operated by cams on the shaft of a waterwheel or on a tappet wheel, which lifted the hammer. These days, the working mill uses hydroelectric power to create electricity for the machines. The river runs down from the Carneddau hills and is channelled into a leaky pipe and then into the generator room, where two big turbines do what turbines do best.
I didn't have much time to dash round and see everything before they closed, so unfortunately I'm not going to be able to explain any of the photos - what they are, how stuff works, what it's called, who built it, when, why, how etc. I'm just going to put the pictures up and let them speak for themselves. If you want to know any practical stuff, go and visit yourself!
more in the next comment...