BUTTERFLY VALVES typically include a circular valve member or disc which is rotatably mounted inside a valve body having a generally cylindrical bore defining a flow passage. O-rings formed from a soft seating material have been used to provide a fluid tight seal when the disc is in a closed position. The O-ring either is mounted in a peripheral groove on the disc and engages a seating surface in the valve body bore or is mounted in an annular groove provided in the valve body bore and is engaged by the outer periphery of the disc.Butterfly Valves Such O-rings are quite acceptable for valves used in low pressure systems but can cause operational problems for valves used in high pressure systems.

Immediately after sealing engagement of the O-ring is broken during initial opening of the valve or immediately prior to establishing sealing engagement during final closing of the valve, a high pressure differential exists across the disc at the constricted opening between the disc and the valve bore. This differential pressure produces fluid forces which tend to cause the O-ring to be dislodged from or "blown out" of its mounting groove and/or pinched between the disc and the valve bore. Prior attempts have been made to alleviate this problem; however, these attempts have not been completely successful, either because the "blow out" problem has not been completely eliminated or the added structural complexities resulted in a substantial increase in the overall costs of the valve.

Examples of prior art arrangements for retaining O-rings are disclosed in U.S. Pat. Nos. 3,234,966 (Klose) and 2,282,010 (Bryant). Butterfly ValvesIn the construction disclosed by the Klose patent, a curvilinear portion including a plurality of circumferentially spaced, longitudinally extending grooves is provided in the valve body bore. Such a construction requires relatively complex and expensive fabrication techniques. In the construction disclosed by the Bryant patent, a relatively complex retainer is used to mechanically retain the O-ring in its groove and the disc is provided with a plurality of circumferentially spaced grooves which serve as flow passages during initial opening or final closing of the valve. These grooves tend to decrease the time for equalizing the differential pressure across the valve during initial opening or final closing; however, they may not always provide rapid enough pressure equalization to prevent the O-ring from becoming at least partially dislodged from its groove, particularly when the valve is used in higher pressure systems and/or the disc is quickly opened or closed.

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