Abstract: A hoop seal for a large annular opening having a high strength ring disposed in the hoop, the hoop having a sealing lip extending at an angle into the high pressure side of the seal, a base and a membrane connecting the hoop to the base which allows the hoop to rise on the side where the annular opening narrows and thereby provide a lateral force which acts to equalize the annular opening.

Abstract: A seal for a large annular opening between two generally cylindrical surfaces. The seal being formed of a first portion having a base ring and a toroidal shaped arcuate portion extending from the central portion of the base ring, a lip portion extending radially inwardly and toward the high pressure portion from the end of the arcuate portion and a second portion having a base ring, both base rings being affixed to one of the cylindrical surfaces. The second base ring being disposed on the high pressure side of the first base ring and there being ribbons extending between the first portion and the second portion. The ribbons being made of a high strength material and being disposed on a predetermined pitch and attaching the free end of the first portion to the second portion to prevent the arcuate toroidal shaped portion from inverting, even though it is compliant and deforms substantially under pressure.