A microsystem for converting pressure difference in fluid into mechanical displacement includes input and output nozzles, two interleaved parts, one of which is mobile part, between which the fluid flows. During displacement, the parts define an expanding fluid pocket that moves from the input nozzle to the output nozzle. The micro-system also includes top and bottom planes between which the mobile part is mounted for displacement relative to each plane, an overhanging distal portion along which the fluid flows, and a proximal portion mechanically linked to a plane via a link allowing only longitudinal translation of the proximal portion, and a reinforcement including a first side fastened to one of the planes and, a second side that is either fastened to or in sliding contact with the overhanging distal portion of the mobile part to limit its deformation in a transverse direction perpendicular to the longitudinal direction.