Power unit for dam

A power unit for a dam having a vertical barrier for retaining a body of water on one side to provide a pressure head comprising, in combination, water driven power generating means, a downwardly inclined main conduit communicating at one end with a horizontal conduit end portion communicating with said body of water through said vertical barrier at a lower portion thereof and communicating at the other end with said power generating means, said conduit having an upwardly extending U-shaped section intermediate the ends of said conduit, said U-shaped section including a bight portion disposed above the level of said body of water, first valve means in said conduit for permitting water to flow from said body of water through said conduit including said U-shaped section into said power generating means and means for initially filling said U-shaped section of said conduit with water flowing to provide a siphon action and to increase the pressure of water flowing into said power generating means wherein said means for initially filling said conduit U-shaped section comprises a pump in a conduit branch having an inlet and an outlet in parallel with said conduit upstream said U shaped section and means including second valve means for communicating said pump conduit branch inlet and outlet with said conduit.