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A diaphragm valve for opening or closing itself through making direct contact of or through breaking the direct contract of a metal diaphragm with a valve seat disposed inside a body provided with an inlet port and an outlet port. The diaphragm valve includes an elevating member which serves to make

A diaphragm valve for opening or closing itself through making direct contact of or through breaking the direct contract of a metal diaphragm with a valve seat disposed inside a body provided with an inlet port and an outlet port. The diaphragm valve includes an elevating member which serves to make or break the direct contact of the metal diaphragm with the valve seat and which is fusion-bonded to the metal diaphragm.

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What is claimed is: 1. A diaphragm valve for opening or closing a fluid flow path, the diaphragm valve comprising: a metal body provided with a valve seat, an inlet port and an outlet port; a metal diaphragm; a manually or automatically operated stem helically attached inside the metal body so as t

What is claimed is: 1. A diaphragm valve for opening or closing a fluid flow path, the diaphragm valve comprising: a metal body provided with a valve seat, an inlet port and an outlet port; a metal diaphragm; a manually or automatically operated stem helically attached inside the metal body so as to be movable up and down so as to cause the metal diaphragm to make or break contact with the valve seat; and a diaphragm piece helically attached to a lower portion of the stem so as to be movable up and down due to being interlocked with the stem, said diaphragm piece being provided at a lower end thereof with a radially diverged depressing part, being fusion-bonded by welding integrally to the metal diaphragm at a position of a through perforation formed approximately at a central position of the metal diaphragm, and being provided on a lower surface thereof with an arcuate surface part that is always kept in contact with the metal diaphragm at a sealing position of the valve seat and at a time of opening or closing the fluid flow path, the metal diaphragm having a peripheral edge portion mounted on a stepped part formed inside the metal body and having an upper part of the peripheral edge portion immobilized with a diaphragm retainer such that the metal diaphragm is inserted airtighly between the stepped part and the diaphragm retainer, the valve seat having a valve seat surface disposed at a position below the stepped part, and a distance between the valve seat surface and the stepped part being set to be �� of a valve stroke, wherein a portion of the metal diaphragm is displaced toward an upper side of the peripheral edge portion of the metal diaphragm and a portion is displaced toward a lower side of the valve seat surface in both an open state and closed state of the valve. 2. A diaphragm valve according to claim 1, wherein the metal diaphragm is formed of Ni--Co alloy having a given degree of hardness and the valve seat is formed of a metal having a degree of hardness lower than that of the metal diaphragm. 3. A diaphragm valve comprising: a metal valve body defining an inlet port, an outlet port, and a fluid flow path extending therebetween; a valve seat disposed in the metal valve body; a metal diaphragm having a central through hole and an outer peripheral portion mounted to the valve body for closing the fluid flow path by making direct contact with the valve seat, wherein the metal diaphragm includes a central convex portion that projects toward the valve seat and an annular convex portion that projects away from the valve seat in both an open state of the valve and in a closed state of the valve; a valve stem movable toward and away from said metal diaphragm so as to cause the metal diaphragm to make or break contact with said metal valve seat; and a diaphragm piece threadedly connected to the valve stem, wherein said metal diaphragm is fusion-bonded to said diaphragm piece by welding at a position of the central through hole, and said diaphragm piece has an arcuate surface part that is always kept in contact with the metal diaphragm in the open state of the valve and in the closed state of the valve, and wherein said valve seat is positioned at a level that is lower than the outer peripheral portion of said metal diaphragm, and the distance between the valve seat surface and the stepped part is set to be �� of a valve stroke.