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;Bellows Seal Valves 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, API Cast Steel Valvessaid 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,REDUCING VALVES 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.

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