Abstract: A metal diaphragm used in making valves designed for passage of highly pure liquids has, starting at an outer periphery, an outer collar designed to abut a planar base of a valve in sealing fashion and connected to a central part, on which an actuating device of the valve is designed to act, by several annular surfaces stepped upward from a plane in which the diaphragm abuts the base. The annular surfaces are successively inclined from the periphery to the central part. One of the annular surfaces is parallel to the plane in which the diaphragm abuts the base when no force is exerted on the diaphragm.