PRIVATIZATION OF NATURAL MONOPOLIES UNDER ASYMMETRIC INFORMATION

PCT No. PCT/EP96/01634 Sec. 371 Date Jul. 31, 1997 Sec. 102(e) Date Jul. 31, 1997 PCT Filed Apr. 19, 1996 PCT Pub. No. WO96/33336 PCT Pub. Date Oct. 24, 1996An extending prop for underground and tunnel construction, comprising, an outer tube having a closed bottom end, an inner tube telescopically slidable in the outer tube and having a closed top end, and a mechanical locking device adapted to fix the relative positions of the inner and outer tubes. A hydraulically actuated flying piston is arranged in the outer tube and is separated from the inner tube. The piston is adapted to extend the inner tube upon actuation by hydraulic pressure. The piston divides the prop into a bottom chamber enclosed by the outer tube and a top chamber enclosed by the inner tube. A first filling connection is arranged on the outer tube for filling the bottom chamber with a pressure medium for actuating the piston. A second filling connection is arranged on the inner tube for filling the top chamber. The prop is fillable with construction material through the second filling connection over its entire length by displacement of the piston toward the bottom end of the the outer tube.