Butterfly valve

In a butterfly valve including a body containing a through flow passage, and a pivoting disc which cooperates with a seat to control flow through the passage and which divides the passage into a first and second portion, an improved seat arrangement which comprises:

• said first and second passage portions being displaced radially at said seat and interconnected by an annular radially extending wall having a height corresponding to said radial displacement of said first and second passage portions and a curvilinear axial annular recess which constitutes a substantial portion of said height and has a relatively large radius of curvature;
• an endless elastomeric seat ring and a clamping ring each having a radially extending face and being abutted to each other along said radially extending faces, the radially extending face of said seat ring being flat over that entire surface, said clamping ring having an axially extending exterior wall with an outside diameter sufficiently less than the inside diameter of said first passage portion to allow said clamping ring to move axially in said first passage portion, and said seat ring includes an axially extending portion which engages and conforms to the shape of said axial annular recess;
• a plurality of screw threaded elements spaced from one another in the direction of the circumference of the clamping ring and extending through apertures in said seat ring and said clamping ring and into said radially extending wall for adjustably forcing the clamping ring axially to thereby compress said seat ring and produce radially inward bulging of the seating surface;
• and
• said first passage portion and said seat arrangement being configured so that said exterior wall of said clamping ring is uniformly exposed to fluid pressure in said first passage portion and exerts uniform pressure on said seat ring with said valve closed to uniformly increase the bulging of the seating surface so as to provide a tighter seal between said valve and said seat ring.