Penstock - Wikiparency

# Penstock A **penstock** is a pipe, tunnel or gated channel that delivers [[Water|water]] under pressure from a reservoir or intake down to the turbines of a [[Hydroelectricity|hydroelectric]] plant or, historically, to a water wheel.[^kerlin-9] It is where the head is delivered and where some of it is lost: friction in the pipe grows with the square of the flow, h_f = f(L/D)v²/2g, so pushing more water through a given penstock first raises the turbine's power and then lowers it. The most power arrives when friction takes one third of the gross head.[^barmeir-11] <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Penstock.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" allow="accelerometer; gyroscope" title="Penstock — p5.js microsim"></iframe> </div> *Microsim (THY-060): increase the flow and watch the turbine power rise, peak where friction eats a third of the head, and fall; widen the penstock and the peak moves. ILLUSTRATIVE: constant friction factor, 800 m pipe, 120 m head.* Videos: [16:9](https://wikitube-3d-microsims.netlify.app/media/Penstock_16x9.mp4) · [9:16](https://wikitube-3d-microsims.netlify.app/media/Penstock_9x16.mp4) ## Hydroelectric systems and dams In a dam-and-reservoir plant the penstock runs from the intake through or around the dam to the powerhouse; in a diversion plant it carries water from an intake on the river down to a powerhouse below.[^doe-plants] For small private systems, a penstock can collect water on a hillside stream and deliver it to the bottom of the hill, creating head without a dam.[^kerlin-9] Penstocks are made of steel, concrete or plastic pipe, or are tunnelled through rock, and are fitted with valves or gates to shut off flow. ## Watermills At water mills, "penstock" also names the sluice or channel that carried water from the millpond to the wheel, together with the gate that controlled it. ## Similar structures Related structures include headraces and flumes, which carry water in open channels, and surge tanks, which are tall open shafts on long penstocks that absorb pressure surges when valves close. ## Hydraulics The head available at the turbine is the gross head minus the friction loss in the penstock, h_f = f(L/D)v²/2g with v = 4Q/(πD²).[^barmeir-11] Because the loss grows as Q² while the power carried grows as Q(H − h_f), the power is greatest when h_f = H/3: at that flow, raising Q further loses more to friction than it gains in water. A larger diameter lowers the velocity and the loss for the same flow, at a higher construction cost, so penstock sizing is a trade between lost energy and capital. Closing a valve quickly stops a long, fast column of water abruptly and raises a pressure surge, which penstocks, valves and surge tanks are designed to withstand. ## Landfills In landfill engineering, a penstock is a pipe or gate structure used to control and drain leachate or surface water. ## References [^kerlin-9]: Kerlin, Thomas W. (2013). *Future Energy: Opportunities & Challenges*, ch. 9 "Hydroenergy," pp. 203–216 (§9.4 dams and small systems; §9.5 pumped storage; §9.6 river-flow converters). ISA; CC BY 4.0. https://open.umn.edu/opentextbooks/textbooks/future-energy-opportunities-challenges [^barmeir-11]: Bar-Meir, Genick (2025). *Basics of Fluid Mechanics*, version 0.7.5, ch. 11 (pipe flow; Darcy–Weisbach friction factor, Moody diagram). https://open.umn.edu/opentextbooks/textbooks/basics-of-fluid-mechanics [^doe-plants]: U.S. Department of Energy, Water Power Technologies Office. "Types of Hydropower Plants." https://www.energy.gov/eere/water/types-hydropower-plants ### Portal Books - Bar-Meir, Genick (2025). *Basics of Fluid Mechanics*, v0.7.5 — [OTL record](https://open.umn.edu/opentextbooks/textbooks/basics-of-fluid-mechanics); on the [[PORTAL_WT!Thury_Hydrodynamics_Compendium|Compendium]] Fluid core shelf. - Kerlin, Thomas W. (2013). *Future Energy: Opportunities & Challenges* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/future-energy-opportunities-challenges); on the [[PORTAL_Thury_Hydrodynamics_Apex_Spine]] and [[PORTAL_Energy]] shelves. ## External links - [Types of Hydropower Plants](https://www.energy.gov/eere/water/types-hydropower-plants), U.S. Department of Energy  *Connected to the Apex Spine:* Penstock → [[Hydroelectricity|Hydroelectricity]] — [[WT!Thury_Hydrodynamics_Compendium|Compendium]] section 16, *Hydroelectricity*.  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Penstock) : [Wikitube](https://en.wikitube.io/wiki/Penstock) · pinned revision [1301555565](https://en.wikipedia.org/w/index.php?oldid=1301555565) · 2026-09-10 ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Energy]]. --- *Thury station wave · 2026-09-10 · drafted · microsim THY-060 (p5.js) · parent [[Hydroelectricity]].*