The present invention relates to adrive mechanism for a medicament delivery device according to the invention 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.本發明有關用於藥物輸送裝置的驅動機構，根據本發明包含壓縮構件，包含裝盛流體之第一體積的第一孔腔，該壓縮構件亦包含裝盛流體之第二體積的第二孔腔；通道，用於該第一孔腔與該第二孔腔間之流體相通；第一可運動活塞，被配置來密封該第一孔腔；第二可運動活塞，被配置來密封該第二孔腔；其中藉由施加的力量，經由經過該通道之流體流動，該第一可運動活塞或該第二可運動活塞的運動造成該流體之第一體積與該流體的第二體積間之體積的相對變化，使得該個別之第二可運動活塞或該第一可運動活塞亦被運動。
