Seal for a rolling cone cutter earth boring bit

A rolling cone cutter earth boring bit for operation in a fluid-filled borehole, comprising:

• a bit body, said bit body having at least one downwardly extending arm;
• a cantilevered bearing pin extending from said arm;
• a rolling cone cutter rotatably mounted on said bearing pin, said rolling cone cutter having a cone mouth;
• bearing and cutter retaining means between said bearing pin and said rolling cone cutter;
• lubricant between said bearing pin and said rolling cone cutter;
• an outer rigid seal ring positioned around said bearing pin within said cone mouth, said outer rigid seal ring comprising an annular rigid ring that is split to allow radial expansion and contraction, said outer rigid seal ring positioned to be in contact with said rolling cone cutter in said cone mouth;
• an inner rigid seal ring positioned around said bearing pin within said cone mouth, said inner rigid seal ring comprising an annular rigid ring that is split to allow radial expansion and contraction, said inner rigid ring being smaller in diameter than said outer rigid ring and positioned to be in contact with said bearing pin in said cone mouth inside said outer rigid seal ring;
• and
• an elastomer ring located between said outer and inner rigid rings in said cone mouth, said elastomer ring being affixed to said outer and inner rigid rings, whereby fluid in said borehole can cause said elastomer ring to force said inner rigid ring to contract into tighter contact with said bearing pin and said lubricant between said bearing pin and said rolling cone cutter can cause said elastomer ring to force said outer rigid ring to expand into tighter contact with said rolling cone cutter.