1. MUD VALVESIn a diaphragm valve of the class in which an elastomeric diaphragm cooperating with an associated annular valve seat is backed-up by a rigid spring retainer biased by a coiled spring, the improvement wherein said spring retainer is provided at a portion thereof facing said valve seat with a relieved surface spaced away from said diaphragm in the free state thereof to permit an annular sealing portion of said diaphragm to resiliently yield in response to a circumferential undulation of said valve seat.

2. The improved diaphragm valve according to claim 1, wherein in the closed position of the valve said diaphragm is brought into contact with said valve seat throughout the entire circumference of said valve seat.

3. The improved diaphragm valve according to claim 1, wherein said diaphragm is responsive to a pressure variation in a sensing chamber defined by said diaphragm and wherein said spring has such a limited spring force that said diaphragm is operable to open the valve seat in response to a pressure drop in said sensing chamber of less than about 100 mmAq.Forged Steel Valves

4. The improved diaphragm valve according to claim 3, wherein said spring has such a limited spring force that said diaphragm is operable to open the valve seat in response to a pressure drop in said sensing chamber of less than about 50 mmAq.

5. The improved diaphragm valve according to claim 1, wherein said valve seat has an annular bead engageable with said diaphragm and wherein said relieved surface is formed by an annular groove facing said annular bead.Filter

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