A diaphragm valve capable of increasing durability of a diaphragm comprises a valve body internally formed with a valve chamber having an open upper end and a suck-back chamber having an open lower end, between an inlet passage and an outlet passage, and a through hole which provides communication between the valve chamber and the suck-back chamber.Instrument Manifolds The open end of the valve chamber is closed by a first diaphragm which is brought into and out of contact with a valve seat.MUD VALVES The open end of the suck-back chamber is closed by a second diaphragm. The first and second diaphragms are substantially identical in shape. Each circumferential edge portion of the first and second diaphragms is tightly retained by a retaining member mountable to the valve body so that the diaphragms are curved outwardly with respect to the valve chamber and the suck-back chamber respectively.Reducing Valves The first and second diaphragms are connected by a connecting rod passing through the through hole so that the diaphragms are deformed synchronously by operation of an actuator.

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