Mechanically lockable hydraulic cylinder jack

Claim 1

In a hydraulic jack comprising a cylinder and a piston rod assembly movable between a first retracted position and a second extended position relative to said cylinder, means for preventing rotation of the piston rod assembly, means for maintaining said piston rod assembly locked in said second extended position comprising a rotatable shaft extending into said cylinder, locking means operatively coupled to said shaft and movable into engagement with said piston rod assembly in response to rotation of said shaft to thereby lock said piston rod assembly in its second extended position, said locking means being adapted to reinforce said piston rod assembly in said second extended position substantially along said piston rod assembly's entire length, said cylinder including a first closed end and a second open end through which said piston rod assembly is movable, and said locking means is movable into engagement with at least a portion of said piston rod assembly located beyond the second open end of said cylinder when said piston rod assembly is in said second extended position, said shaft extending through the first closed end of said cylinder and wherein a portion of the shaft extending into said cylinder has thread means thereon and said locking means comprises a second cylinder concentrically disposed between said shaft and said first-mentioned cylinder, said second cylinder including thread means for cooperatively engaging the thread means on said shaft to lock the piston rod assembly in its extended position. The locking means reinforces the piston rod assembly in its extended position along substantially the entire length of the piston rod assembly.