The invention relates to a system of bellows and co-acting part, including a co-acting part which comprises a stiff outer wall, and a bellows co-acting therewith which comprises a flexible wall of a predetermined shape and thickness, wherein the flexible wall of the bellows is movable along the stiff outer wall of the co-acting part, wherein the bellows includes at least two separately deformable flexible wall parts' which each co-act with a different part of the stiff outer wall of the co-acting part.