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 inherited from the earlier technology of mill ponds and watermills.[clarification needed]
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 by turbine operation and is nil when turbines are not in service.[clarification needed] Penstocks, particularly where used in polluted water systems, need to be maintained by hot water washing, manual cleaning, antifouling coatings, and desiccation.[clarification needed]
The term is also used in irrigation dams to refer to the channels leading to and from high-pressure sluice gates.
Penstocks are also used in mine tailings dam construction. The penstock is usually situated fairly close to the center of the tailings dam and built up using penstock rings.[clarification needed] These control the water level, letting the slimes settle out of the water. This water is then piped under the tailings dam back to the plant via a penstock pipeline.
Penstocks are commonly used in water management systems such as surface water drainage and foul water sewers.[clarification needed] Penstocks provide a means of isolation of flows and regulate the flow of water while delivering it to waste management facilities or power plants.
Penstocks are incorporated into the surface water management systems (drainage) of many landfill sites. Attenuation lagoons are constructed in order to store storm water,[clarification needed] limiting the discharge from the site to pre-development rate (green field rate).[clarification needed] Penstocks are installed at the outfall from the lagoon so that in the rare event that the surface water becomes contaminated the penstock may be closed. This will have the effect of isolating the site from the watercourse, preventing contamination of the environment.