Site Records

Culligran Power Station - Surge Shaft

Since Culligran is fed by a pressure tunnel, an upstream surge shaft is required to relieve water hammer. It's a differential system, consisting of two shafts, one of large diameter, one small, with an overflow channel between them - an almost identical layout to the one used at Deanie. The drawing on the main Culligran page shows the layout most clearly.

A differential surge shaft typically has the small riser shaft concentric with the large one. The reasons an arrangement of seperate shafts was used here were twofold: Since a gate is fitted to allow dewatering of the high-pressure system (and as a guard gate), use of a seperate shaft upstream of the gate allows the relief of water hammer when the gate is closed. Secondly, since the large shaft is unobstructed, the top of the high-pressure shaft can be contained within its diameter. This is an advantage during construction, as it allows direct access to the high-pressure system from above, from the floor of the surge shaft.

I was fortunate enough to visit Culligran whilst the system was dewatered for maintenance, so I have some pictures of the empty surge chamber. This is a rare event - 99.9% of the time, it's full of water!

Words and images © 2005 Michael J. Ross.