With Metal Seal: The Tri-Seal Flange system is illustrated below.
The metal sealing grove is protected in two ways. The protruding lips prevent contact with flat surfaces when components are being moved, stored or assembled. In addition, the groove is recessed into the metal for additional protection, not exposed as in the case of external knife edge type flanges which are more susceptible to damage. The metal seals are manufactured from 304 stainless steel, copper and aluminum. The seal itself facilitates ease of alignment during the assembly process. An interference fit between the angle of the metal sealing ring and the angle of the flange sealing groove produces a vacuum tight seal without distortion or wear of the flange groove or galling of the metal seal. It is possible to obtain several seals from the same sealing ring if appropriate care is taken.
As aluminum and copper seals are softer than stainless steel, they tend to preserve the integrity of the metal sealing groove, allowing multiple usage of the flange. Frequent replacement of the seal is always recommended.