Lens Rings have a spherical surface and are used on flanges with conical faces. The gasket material should be softer than the flange material, ensuring that the applied compressive load leads to the elastic or plastic deformation of the gasket and not the flange sealing face.
By applying higher loads on the gasket the contact area between the gasket and the flange increases. This prevent the gasket from being overstressed.
As with all metallic joint’s, the re-use of Lens Rings is not recommended.