of a restoring spring 31 acts on the valve closing body 15 in the direction facing away from the valve seat 12 according to the invention the restoring spring 31 is embodied as a tension spring which pulls the valve closing body 15 in the direction facing away from the valve seat 12 the restoring spring 31 is located on the side of the valve closing body 15 facing away from the valve seat 12 for instance in the ventilation chamber 19 in the ventilation chamber 19 the restoring spring 31 is located between the edge 24 of the diaphragm 15 and the valve cap 3 beginning at the edge 24 of the diaphragm it extends toward the diametrically opposite edge 24 of the diaphragm and rests loosely on each edge 24 of the diaphragm and is supported for instance on both of its ends in a respective recess 35 of the valve cap 3 the recesses 35 in the valve cap 3 are each located in the region of the annular edge 24 of the diaphragm in the region of the valve axis 30 the restoring spring 31 is connected in form locking material locking or force locking fashion to the valve closing body 15 for instance to the valve closing portion 23 the restoring spring 31 of the invention is for instance a leaf spring or a barlike spring which is made from a flat steel or wire shaped round steel and is manufactured from spring steel upon the axial motion of the valve closing body 15 in the direction of the valve seat 12 the restoring spring 31.