Patent ID: 7530300

Claim:
A lifting device comprising: two cylinder tubes for moving synchronously with one another vertically; each cylinder tube comprising a hydraulically operated lifting unit and an internal seal at its lower end; a mechanical transverse support attached to the two lifting units for ensuring the synchronization of the two cylinder tubes and for preventing the two cylinder tubes from rotating about their longitudinal axis; and a mechanical anti-lowering means for preventing unintentional lowering in the event of a pressure loss; wherein each lifting unit includes a stationary, hollow plunger piston having a cavity that is supported at a base, the piston includes a tube within the piston cavity that extends from a point near a first end to a second end of the piston, the piston tube includes an opening located near the second end of the piston, the piston tube receives compressed air and the cavity within the piston external to the piston tube receives hydraulic fluid, wherein the plunger pistons include at the first end of the plunger pistons a first opening for receiving compressed air into the piston tube and a second opening for allowing the flow of the hydraulic fluid.