A piston rod sealing system with a sealing unit, for preventing leakage, of gas from a high-pressure chamber to a low-pressure volume, and preventing leakage of a lubricant from said low-pressure volume to said high-pressure chamber, along a piston rod, which is included in said piston rod sealing system, extending through said chambers (4, 6) said sealing unit, which is included in said piston rod sealing system, comprising, - a deformable gland (10,21,26) arranged for being pressed against said piston rod by one or more compressing elements (15, 22, 27), - a lubricant between the piston rod and the gland (10, 21, 26), said sealing unit arranged between, - a support structure, which is included in said piston rod sealing system, in the low-pressure volume with a plane sliding surface facing towards said sealing unit, - and a wall, which is included in said piston rod sealing system, of said high-pressure chamber, - a plane seal constituting a seal between the sealing unit and said wall, said plane seal arranged in a groove (13b, 24a, 26e) in said sealing unit, said groove open towards said wall, or said plane seal arranged in a groove in the wall, said groove open towards said sealing unit, wherein, - said sealing unit having a surface area towards said wall between said piston rod and said plane seal smaller than the sliding area between said sealing unit (9, 12b, 25a, 28a) and the plane sliding surface, and - said sealing unit being supported by said plane sliding surface on the low-pressure side, and said sealing unit being in sliding contact with said wall surface, the length (L') of said sealing unit is less than the length between the support structure and the wall allowing transverse movement of the sealing unit along the sliding surfaces (7a, 8a). said sealing unit, which is included in said piston rod sealing system, comprising, - a deformable gland (10,21,26) arranged for being pressed against said piston rod by one or more compressing elements (15, 22, 27), - a lubricant between the piston rod and the gland (10, 21, 26), - a deformable gland (10,21,26) arranged for being pressed against said piston rod by one or more compressing elements (15, 22, 27), - a lubricant between the piston rod and the gland (10, 21, 26), said sealing unit arranged between, - a support structure, which is included in said piston rod sealing system, in the low-pressure volume with a plane sliding surface facing towards said sealing unit, - and a wall, which is included in said piston rod sealing system, of said high-pressure chamber, - a support structure, which is included in said piston rod sealing system, in the low-pressure volume with a plane sliding surface facing towards said sealing unit, - and a wall, which is included in said piston rod sealing system, of said high-pressure chamber, - a plane seal constituting a seal between the sealing unit and said wall, said plane seal arranged in a groove (13b, 24a, 26e) in said sealing unit, said groove open towards said wall, or said plane seal arranged in a groove in the wall, said groove open towards said sealing unit, wherein, - said sealing unit having a surface area towards said wall between said piston rod and said plane seal smaller than the sliding area between said sealing unit (9, 12b, 25a, 28a) and the plane sliding surface, and - said sealing unit being supported by said plane sliding surface on the low-pressure side, and said sealing unit being in sliding contact with said wall surface, the length (L') of said sealing unit is less than the length between the support structure and the wall allowing transverse movement of the sealing unit along the sliding surfaces (7a, 8a).