Abstract: A valve seal for a butterfly valve comprises a U-shaped annular seating member disposed in an annular slot in the valve body and a retaining ring for holding the seating member in place. The seating member cross-section comprises two legs and a bight portion connecting them. A first one of the legs is captured between the retaining ring and valve body to hold the seating member in the slot and enable limited rotational movement of the seating member. A radially inwardly projecting extension on the bight terminates in an annular sealing surface that cooperates with the valve disc. The seating member divides the slot into first and second axial sides in fluid pressure communication with the valve chamber. The seal also comprises an annular open-helical back-up member disposed in an annular cavity formed in the slot by the legs and bight portion of the seating member. The annular cavity is in fluid pressure communication with the second axial side of the slot.