the planar surface 36 of the glass substrate 32 beside the inlet orifice 35 of the flow duct 34 the face of the silicon plate 44 which is in register with the membrane 38 is not entirely planar but has a contact surface 45 connected to the surface 36 of the substrate 32 away from the membrane 38 the zone of the plate 44 which is in register with the membrane 38 is shaped so as to form a chamber 46 in which liquid can flow provision is made for this chamber 46 which is situated between the substrate 32 and the silicon plate 44 to extend beyond the zone of the micropump shown in fig3 and constituting the valve 30 of the present invention towards liquid inlet means the zone of the plate 44 situated in register with the orifice 42 of the membrane 38 has an annular projection 48 whose cross section as shown in fig3 appears as two tapering quadrilaterals the inside space within the projection 48 is likewise tapering and constitutes the space 50 which is in line with and in register with the orifice 42 in the membrane 38 and with the flow duct 34 in the glass substrate 32 provision is made for the free end of the annular projection 48 to be in contact with the central zone 39 of the membrane 38 around the orifice 42 when the valve 30 is in its rest position thus when the valve 30 is in its rest.