Abstract: A non-return valve element comprises a one piece moulding of resilient rubber material, for example a synthetic rubber, which is shaped to include a relatively thick and hence rigid planar rib 1 of which the upper edge 1a includes a cylindrical protuberance 2 forming a reinforcement against longitudinal and transverse deflections. The lower edge 1b of the rib has two integral laterally extending wings 3 and 4, each of which is semi-circular in plan. The wings together in planform are circular and are designed to fit a cylindrical bore 5 provided in a fluid flow channel. The bore 5 is delimited from a narrower cross-section bore 6 by means of a shoulder 7 forming a seating for the wings 3 and 4, and an abutment for the ends 8 and 9 of the edge 1b of the rib 1.