Nonreturn valve, in particular for medical infusion appliances

A nonreturn valve, in particular for use in connection with medical infusion appliances, comprising a housing with a central chamber into which open an inlet channel and an outlet channel, the channels being separated by a sealing membrane provided with a flow passage, wherein the membrane has a marginal part clamped in the housing, a central sealing part having a sealing surface, and a thinner annular wall that links both parts, wherein an inner wall side of the chamber (9) facing the outlet channel (7) comprises a sealing system for the membrane, the sealing system comprising a central crater-like ring having an annular sealing edge, wherein inflow from the inlet channel (6) to the membrane (10) takes place outside the crater-like sealing ring, and the flow passage (18) of the membrane (10) is located as an aperture within the crater-like sealing ring, wherein the thinner annular wall (17) of the membrane (10) generates a sealing prestress between the annular sealing edge and the sealing surface, and junctures (17a, 17b) adjacent to the marginal part (16a) and to the central sealing part (16b) of the membrane, the junctures being substantially coplanar with the sealing surface of the central sealing part (16b) and the annular sealing edge of the crater-like sealing ring.