The present disclosure relates to adrive mechanism for a medicament delivery device according to the disclosure comprises a compression member comprising a first cavity containing a first volume of fluid, said compression member also comprising a second cavity containing a second volume of fluid； a passage for fluid communication between the first cavity and the second cavity； a first movable piston arranged to seal the first cavity； a second movable piston arranged to seal the second cavity； wherein movement of the first movable piston or of the second movable piston, by an applied force, causes a relative change of volume between the first volume of fluid and the second volume of fluid, via a fluid flow through said passage, such that the respective second movable piston or the first movable piston is also moved.
