Valve housing including a valve chamber incorporating fluid inlet and outlet conduits and a valve seat, and said valve assembly disposed within said housing and comprising a valve stem and stem collar; said valve stem movable engaged within said collar and extending beyond said collar at both ends and having a first intermediate radially expanded flange disposed about the intermediate portion of said valve stem and within said collar and a second radially expanded terminal flange spaced from said first flange and provided about the lower end of said valve stem and below the level of said collar; said intermediate and terminal flanges being connected by a constricted neck; an angular stop ring disposed about said valve stem and in spaced relation thereto below the level of said collar; Bellows Seal Valvesa swivel bearing cup having a rim abutting said terminal flange of said valve stem; a resilient, compressible, annular valve diaphragm including a radially expanded end closure means, sealing ring and a constricted interconnecting neck, said end closure means being secured about said swivel bearing cup in spaced relation to that portion of said terminal flange encapsulated by said swivel bearing cup, said swivel bearing cup being disposed adjacent to said constricted neck of said valve diaphragm, and said closure means being adapted to seat on said valve seat to impede fluid flow through said valve chamber when said valve assembly is disposed in a closed position; said swivel bearing cup and valve diaphragm end closure means being adapted to move toward and away from said valve seat with corresponding axial movement of said valve stem; said valve stem being adapted to rotate independently of said swivel cup and said diaphragm in affecting said axial movement; said sealing ring being secured to said stop ring and mounted thereon in spaced relation about said valve stem; and said constricted interconnecting neck being adapted to axial expansion and contraction with movement of said stem, said swivel bearing cup and said diaphragm end closure means toward and away from said valve seat; Balance Valvesthe improvement that comprises a radial space provided between the upper portion of said neck of said valve stem and the inner diameter of said stop ring such that said space comprises up to about 160 percent of the thickness of said diaphragm neck to assist in preventing undue involution or collapse of said constricted neck of said valve diaphragm when said end closure means is withdrawn from said valve seat to prolong the life of said valve diaphragm.

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