Hollow metal sealing rings

A seal comprising in combination:

• first and second members to be sealed, each said member having thereon a sealing surface, with the respective sealing surfaces substantially parallel to each other and mutually opposite to and spaced from each other;
• and a resilient metal sealing ring axially compressed and decompressed between said surfaces;
• said metal sealing ring having a radial cross-section which is hollow and is open at the radially innermost side of the ring cross-section and comprises axially spaced first and second limbs resiliently compressible and decompressible axially towards each other, each said limb having a respective axially outwardly facing convex arcuate contact line intermediate its radial extent for sealingly contacting a respective said surface, wherein the configuration of said seal ring is such that each said limb does not substantially deform upon use, and having a respective radially inner region, said limbs being joined together in the radially outermost region of said ring cross-section;
• said radially outermost region being of increased thickness relative to the limbs such as to increase the hoop strength of the ring locally at said radially outermost region so as not to permit the permanent deformation of said sealing ring, and having a substantially cylindrical radially outermost external surface;
• each said radially inner region having an axially outwardly facing convex arcuate external surface, with the respective said external surfaces being mutually convergent with decreasing radius towards said radially innermost side of said ring cross-section, said limbs defining in cross-section an internal profile which is of smoothly blended, concave arcuate form at least in the radially outer portion thereof.