The cylinder is filled with a hydraulic fluid and carries a sliding piston with a rod (3) which passes through a sealing block in one end of the cylinder. A double seal (20) within a groove (34) lies in the block, and comprises a seal (18) pressed against the rod by an O-ring (19). The groove has a removable section (31) on its side away from the piston. This section has a shoulder (48), extending towards the other side, which supports the seal and absorbs any compression force applied to the O-ring via the rod seal.
