penstock

thumb|Penstocks at the Ōhakuri Dam, New Zealand A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydro turbines and sewerage systems. The term is of Scots origin, and was inherited from the earlier technology of mill ponds and watermills, with penstocks diverting pond waters to drive the mills.

==Hydroelectric systems and dams== thumb|Hydroelectric turbine penstock cross-section thumb|The five penstocks of Shasta Dam, California, seen from above Penstocks for hydroelectric installations are normally equipped with a gate system and a surge tank. They can be a combination of many components such as anchor block, drain valve, air bleed valve, and support piers depending on the application. Flow is regulated to suit turbine operation and is cut off when turbines are not in service. Penstocks, particularly where used in polluted water systems, need to be maintained by hot water washing, manual cleaning, antifouling coatings, allowing waters to go anoxic, and desiccation used to dry fouling out so that it may slough off or become easier to remove through manual processes.