|The Large-Flange™ family is specifically intended to utilize an O-ring with a circular cross-section. The O-ring is held in place by a centering ring. The O-ring seal is made on the flat surface of the flange outside the O-ring groove. The O-ring does not sit inside the groove itself. The centering ring is necessary, otherwise the flexible O-ring would be distorted by external air pressure and the seal would fail.
O-rings are intended for repeated seals. Viton® O-rings have a usable temperature range from -20°C to 200°C (intermittent), with a sustained temperature rating of 150°C. Note that repeated bakeout to 200°C can cause deterioration of O-rings and require their periodic replacement.