Adjustable draft tube

Claim 1

A hydraulic turbine installation comprising: a foundation structure separating a high elevation headwater from a lower elevation tailwater with a water level in said tailwater variable between a predetermined high tailwater level and a predetermined low tailwater with said foundation structure presenting a generally vertical wall on the downstream side within said tailwater reservoir and a generally horizontal floor extending away from said wall into said tailwater; a water passageway formed through said foundation having an inlet in communication with said high elevation reservoir and an outlet in communication with said low elevation tailwater with said passageway being generally rectangular and having a lower surface flush with said floor and said passageway having a roof member and opposing side walls flush with said outlet; a turbine runner rotatably supported within said passageway intermediate said inlet and outlet; an adjustable draft tube portion provided on the downstream side of said vertical wall and within said tailwater comprising a pair of vertical side walls each comprising a pier having a generally rectangular cross-section box frame with a plurality of reinforcing ribs secured to interior surfaces of said frame and a floor plate spaced from said tailwater floor to define a plurality of cavities within each pier; means for securing upstream edges of said sidewalls to said foundation structure with said passageway outlet disposed between said side walls; means for securing said side walls to a floor of said tailwater; a draft tube roof member comprising a flap having an end pivotally secured to said foundation structure above said outlet with said roof member generally horizontal and pivotal about a generally horizontal axis of rotation; said flap extending between said side walls and pivotal about said axis with a free end of said flap movable between a first position beneath said predetermined low tailwater level and a second position between said predetermined low tailwater level and said predetermined high tailwater level; a pair of horizontally axially aligned opposing trunnions secured to said frames, a torque tube extending between piers and carried by said trunnions for pivotal movement about a horizontal axis central of said tube, and said flap secured to said tube for pivotal movement therewith; and means for pivoting said flapo with said free end moving between said first and second positions.