Pressure insensitive lip seal

Claim 1

A lip seal for dynamically sealing a low pressure cavity against entrance of a variable higher pressure fluid between said seal and a rotating shaft, comprising: a housing within which said shaft rotates; an annular flange extending generally radially and having a radially outside edge which is clamped to said housing and a radially inner edge; an annular, axially extending resilient bushing having a proximate end attached to said radially inner edge of said flange and a distal end; an annular foot integrally attached to said distal end of said bushing and extending axially therefrom into said low pressure cavity; biasing means urging said distal end of said bushing and said foot into contact with the said shaft; a radially inward facing surface on the bushing and said foot adapted to engage said shaft in a sealing relationship; a hydrodynamic profile formed in said inwardly facing surface and arranged to generate a pressurized fluid film between said surface and said shaft, which pressure is a function of the variable higher pressure exerted on the radially outward face of said bushing, whereby the fluid film pressure compensates the variable higher pressure so as to maintain said sealing relationship; an annular pocket located on the axial side of said hydrodynamic profile nearest said variable higher pressure fluid and adjacent the junction of said foot and bushing for providing a pressurized oil containment plenum for said seal; and duct means extending through said bushing and providing communication between said annular pocket and said oil cavity for relieving excess pressure in said pocket means.