Gas lubricated slow speed seal

A gap type mechanical end face seal for providing fluid sealing between a housing and a rotatable shaft extending through a bore in the housing, the seal having an annular primary ring and a relatively rotating annular mating ring, each said ring being annularly symmetrical about a centerline and each having a seal face in opposed mating sealing relation to the seal face of the other ring, an inner diameter peripheral edge and an outer diameter peripheral edge, one peripheral edge of said annular rings being configured for contact with pressurized fluid to be sealed within the housing and the other peripheral edge being configured to be exposed to and in contact with a gaseous environment outboard of said seal, upon installation, said primary ring being axially movable relative to the shaft or housing and said axially movable primary ring being sealed to either the shaft or housing by a primary ring secondary seal, said mechanical end face seal further comprising a biasing means for biasing said axially movable primary ring tending to bring said opposed mating seal faces toward contact with each other, said seal face of said axially movable primary ring further including a plurality of grooves extending partially across the face from the peripheral edge exposed to the gaseous environment outboard of said seal and toward the peripheral edge exposed to the pressurized fluid, each of said plural grooves terminating intermediate said peripheral edges at a circumferential terminal segment to define an annular groove area adjacent said peripheral edge exposed to the gaseous environment outboard the seal and an ungrooved dam adjacent said peripheral edge exposed to the pressurized fluid, the radial width of the seal face of the axially movable primary ring being substantially less than the radial width of the seal face of said mating ring, such that during seal operation, the seal face of said mating ring at all times overlaps the annular groove area of the axially movable primary ring in an opposing mating relation, and rotation of one of said rings relative to the other causes said grooves to pump a gas from the gaseous environment adjacent the peripheral edge to which said grooves open toward said dam, said grooves pumping gas between said seal ring faces and thereby causing a fluid film gap to form between said seal ring faces, so as to provide a leak-tight seal preventing fluids leaking along said shaft and through said bore from said housing and into the gaseous environment outboard said seal.