Ball valve seat seal

A ball valve (10) includes a body (A) having a passageway (12) extending there through with a ball member (B) disposed in the passageway (12) and mounted for selective rotation between valve open and valve closed positions to control fluid flow through the valve (10). A pair of flange grooves (34) are provided in the body (A) on opposite sides of the ball (B), each flange groove (34) extending radially from the passageway (12). A pair of seat rings (16) are disposed in the passageway on opposite sides of the ball (B). Each seat ring (16) has a first sealing surface (24) in contact with an outer surface (26) of the ball (B) and a radially extending annular flange or tab (30) received in an associated one of the flange grooves (34). The seat (16) design further includes a pair of annular flange seals (18) each disposed in a respective one of the flange grooves (34). The seat (16) material is preferably made of a relatively harder and stiffer material compared to PTFE, such as PEEK. The seat (16) configuration achieves a cantilever effect to improve the temperature and pressure cycling performance of the valve (10). The flange seals (18) are preferably made of elastomer material or metal seals having spring-like characteristics.