NOTICE: This photograph is reproduced courtesy of the North Otago Museum. No further copying of this image is permitted without their agreement. Here, in this 1916 or 1917 photograph from the Smyth Collection (courtesy North Otago Museum) we can see both the 18" and 24" main water supply pipes - flow is from left to right- which were laid down The Glen when the Borough Race and reservoir of the town water supply for Oamaru was constructed in 1880. These are huge pipes by any standard and monstrous for such a small town supply. They are cast iron, are about 30mm wall thickness and were supplied by Andersons Engineering in Christchurch. They almost certainly were made by Alley and Mclellan in Glasgow - they made all the valves and fittings - As far as I can see each was 12 feet long and the 24 inch pipes would have weighed about 2 tons each.
In 1916-17 They were both breached at the top of Glen Road by Hutchinsons Quarry and a steel fabricated and riveted bifurcated splice fitted to lead water from both pipes to the 3' diameter staved wooden penstock to the power station in Cross Street where a Pelton wheel and AC generating set had been installed in a purpose built building adjacent to the Public Gardens and to Oamaru Creek which would take the discharged water. It appears from this photo that only the 18" pipe had a valve in it and the 24" pipe was permanently connected to the penstock. In the event, the friction in the wooden penstock (and the total length including the town pipes down the hill) rendered the Pelton wheel under powered for the generator set and relatively soon after commissioning it was seen to be unable to meet the growing load as citizens quickly cottoned on to the benefits of 230volt AC at their doorstep!
This whole installation was one of New Zealand's earliest distributed AC systems and possibly the third in the country to be provided by a public territorial authority. A number of New Zealand's pioneer hydro electric and steam driven power supplies for towns and cities were installed by private companies and individual engineers.