The present invention provides a diaphragm valve including a housing having a chamber and an outlet opening within the chamber. A projecting valve seat, formed by a projection extending into the chamber, has a sloping, annular sealing surface surrounding the outlet opening. A valve body, preferably forming an armature of an electromagnetic coil, is also located within the chamber. The valve body has, at one end, a recess and a metal diaphragm covering the recess and chemically non-reactive with a flowing fluid passing through the chamber and out of the outlet opening. The valve body is adapted for movement towards and away from the valve seat between closed and open positions. In the closed position the diaphragm is flexed into the recess by the projection, conformingly and sealingly contacting the sealing surface and covering the outlet opening, to prevent the passage of flowing fluid. In the open position, the diaphragm is spaced from the valve seat and the outlet opening is uncovered to allow passage of the flowing fluid. The diaphragm is prestretched before attachment to the valve body so that the diaphragm conforms to the sloping sealing surface of the valve seat rather than creasing above the valve seat.