System for blocking relative translational movement between two parts

A system for securely blocking relative translational movement between a cylindrical shaft and an element , includes a blocking element in which an immobilization element is arranged, the immobilization element being associated with a viscoelastic fluid disposed between the blocking element and the immobilization element in such a way that translational movement is blocked when the viscoelastic fluid is pressurized in the blocking cylinder and translational movement is possible when the viscoelastic fluid is no longer pressurized. An actuating cylinder equipped with such a secure blocking system is also described.