Dynamic seal assembly for piston and cylinder operating in subterranean wells

Claim 1

A bi-directional dynamic seal for a piston element concentrically mounted in a vertical cylindrical bore of a well tool for axial movement relative thereto, comprising: a first primary seal having a hub portion concentrically and sealably mounted relative to the exterior of said piston element; said first primary seal having a frustroconically shaped, annular skirt portion extending radially and downwardly from said hub portion into sealing engagement with the wall of the well tool defining said cylindrical bore; a second primary seal having a hub portion concentrically and sealably mounted relative to the exterior of the piston element in upwardly sapaced relation to said first primary seal; said second primary seal element having a frustroconically shaped annular skirt portion extending radially and upwardly from the respective hub portion into sealing engagement with the wall of said cylindrical bore; both said first and second primary seal elements being formed from a non-metallic, non-elastomeric sealing material; a metallic secondary seal element comprising a tubular body securable to said piston element intermediate said hub portions of said first and second primary seal elements, the axial end portions of said tubular body respectively defining frustro-conical, annular flexible lip portions respectively snugly surrounding said skirt portions of said first and second primary seals; each said lip portion having an external cylindrical surface of slightly smaller diameter than said cylindrical bore, whereby the application of a fluid pressure in either direction to said piston element causes one of said primary seals to expand and resiliently expand the adjacent secondary seal to force the external cylindrical surface of the adjacent lip portion into sealing engagement with said cylindrical bore.