Disc valve

In a valve including a valve body having a valve chamber therein containing a valve disc adapted to be turned between open and closed positions, and an annular groove in the valve body surrounding the valve chamber opposite the outer periphery of the disc when the disc is in the closed position, the improvement comprising:

• a seat ring in said groove having a first portion relatively inflexible so as to maintain the seat ring in position within said groove and a second relatively flexible portion formed as one piece with the first portion and extending generally axially from the first portion, the second portion terminating in an unsupported free end such that the first portion of the seat ring provides support for one end of the second portion thereof and the other end of the second portion of the seat ring is unsupported against radial contraction, and wherein the second portion has an outer diameter less than the diameter of said groove to form a cavity around the second portion;
• first means forming a first vent between the valve chamber at one side of said groove and said cavity at one end of the relatively flexible portion of the seat;
• second means forming a second vent between the valve chamber at the opposite side of said groove and said cavity at the opposite end of the relatively flexible portion of the seat;
• and
• elastomeric means in said cavity for closing the first vent when the second vent is exposed to the higher pressure and for closing the second vent when the first vent is exposed to the higher pressure so that the larger fluid pressure exerted at either side of the disc with the disc in a closed position is transmitted to said cavity to force the relatively flexible portion of the seat ring against the disc.