US Patent 7100897 Hydraulic jack

Disclosed is a jack lever, in which oil is pumped by piston (10) to move a cylinder (20) faster, vacuum being created at a lower portion of the cylinder (20) moving up, oil in an oil tank (101) being then flowed in the lower portion through an oil suction channel to make the cylinder move up faster. If the cylinder (20) moves upward to push up a work piece, load is exerted into the cylinder (20), so making the piston (10) pumping oil stronger, the oil opening a check ball (15a) mounted on a bypass channel (15) by the pumping and being supplied to the lower portion of the cylinder (20) to move the cylinder up. At this time, the cylinder (20) moves slower but increases ascending force, thus requiring small power to manipulate a jack lever (not shown) pumping the piston (10).