Cryogenic valve seal

Claim 1

A valve for cryogenic service, the valve including a valve body having a fluid inlet and a fluid outlet connected by a passageway, an annular seating region defined by an interior circumferential surface of the passageway intermediate the inlet and outlet, and an annular undercut circumferential groove formed in the wall of the passageway in said seating region; a valve member having a circumferential sealing surface; means for rotatably mounting the valve member in the passageway for selective rotational movement of the sealing surface into and out of opposed relation to the groove; a resilient wear ring of a fluorinated hydrocarbon material disposed in the groove and movable radially inward and outward therein, the wear ring having an inner circumferential seating portion protruding radially inward from the groove into the passageway and an outer circumferential shoulder portion within the groove, the inner circumference of the seating portion forming a radially inward facing seating surface which makes an interference sealing fit with the sealing surface of the valve member when the valve is shut, and the outer circumference of the shoulder portion having a radially outward facing annular channel formed therein, the sides of said channel being bevelled outwardly to provide said channel with an at least partly V-shaped cross section, said channel dividing the shoulder portion into two axially-spaced annular parts the outer edges of which bear against the respective adjacent sides of the groove; and a backing ring disposed in said groove between the channel of the wear ring and the radially outward region of the groove, said backing ring urging the seating portion of said wear ring radially inward from said groove and urging the outer edges of the spaced annular parts of the shoulder portion against the respective sides of the groove, wherein the improvement comprises: said backing ring being made of a metal having a relatively low modulus of elasticity combined with high yield strength at both normal ambient and cryogenic temperatures and formed as an annular band having an inner circumferential surface which is bevelled outwardly from a central region to both sides of the band to provide a solid trapezoidal wedge-shaped cross section, the bevelled sides of said wedge-shaped inner circumferential surface of the backing ring making a predetermined interference fit with the bevelled sides of said channel of the wear ring, and wherein the wedge angle of the bevelled inner circumferential surface of the backing ring is about 90° and is greater by about 10° than the angle between the bevelled sides of the channel in the shoulder portion of the wear ring, whereby the backing ring exerts pressure against the bevelled sides of the channel in the wear ring to provide effective sealing at the seating surface and both outer edges of the annular parts of the wear ring at valve operating temperatures from ambient down to cryogenic.