The knife-edge design of a Del-Seal™ flange is specifically intended to utilize a flat copper gasket as the most common method of sealing. A special electrolytic grade copper ensures vacuum compatibility. The two knife-edges of face-to-face flanges dig into the gasket material and form a superior vacuum seal. Small imperfections in a knife-edge are filled in with material as the gasket is deformed. Nicks that are too large to be filled in by gasket material require flange replacement. Circular scratches on a gasket can be tolerated, but radial scratches may provide a leak path across a knife-edge and gaskets with those imperfections should not be used.
Copper gaskets are intended for a one-time use. Once deep grooves have been cut into the gasket by a knife-edge, it is questionable if the gasket will provide a subsequent reliable seal. Although it is not impossible to reuse a copper gasket, MDC does not recommend this practice. Instead, for multiple reuse, an elastomer material may be used. Viton® gaskets with a rectangular cross-section are available for frequent assembly and disassembly during initial system set-up.
The major advantage to having a metal seal is the level of vacuum that can be attained. Hand-in-hand with the vacuum range is the increased temperature range possible with metal gaskets. Elastomer gaskets will soften and eventually break down if subjected to high heat or even moderate heat for an extended period. Metal gaskets allow a system to be baked at temperatures of 200°C or higher in order to drive water vapor out of the system.