The membrane valve has its membrane (5) in a casing consisting of an upper part (7) and a lower part (1). The membrane has an edge bulge (12). It is stretched in the chamber (11) formed by the casing parts by means of bolts (6). There is a flap-like extension (16) moulded onto the bulge. The extension is fitted between the corresponding endfaces of the upper and lower parts of the casing. It may have a sealing lip lying on the endface of the lower part of the casing, and may also have apertures (19) for the bolts used to stretch the membrane.
