US Patent 7568504 Hydraulic cylinders and plug with hydraulic cylinder

The invention regards a hydraulic cylinder (1) or a plug comprising a hydraulic cylinder for operation of anchoring and or sealing devices, where the hydraulic cylinder comprising a cylinder chamber (6), a piston head (4) within said cylinder chamber (6) forming two sub chambers (7, 7′) of said cylinder chamber (6) one on each side of the piston head (4), and a piston rod (5) which runs through the piston head (4) and said two sub chambers (7, 7′) or only one of said cub chambers. The hydraulic power unit (8) for operation of the hydraulic cylinder (1) is situated at least partly within the parts forming the hydraulic cylinder (1) itself, preferably the piston head (4) and or the piston rod (5).