Hydraulically-operated machines

A hydraulically-operated low head machine of large diameter, in excess of 20 feet, adapted to receive water at an upper level from a relatively large reservoir and to discharge the water to a lower level, which includes:

• a hollow ballasted piston head carried upon a piston rod for movement in a concrete cylinder structure, said piston rod being mounted for vertical movement in guide bushes located above and below the piston head, said cylinder structure being formed of a wall having a thin flexible liner on a bed of grouting between said liner and a wall of a cavity in said concrete structure, said liner being positioned in said cylinder wall through relative movement in one stroke of said piston head to provide a uniform gap of minimum dimension relative to the piston head over its entire stroke, control valve means;
• said control valve means being disposed in control valve passage means;
• and said control valve passage means comprising, concrete inlet control valve passage means and gates for allowing water to flow from the upper level alternately to the upper and lower surfaces of the piston head, and concrete outlet control valve passage means for allowing water on the respective other side of the piston head to flow to the lower level.