Fail safe high pressure shaft seal

Claim 1

In a shaft seal assembly for a pump having a pump housing and a drive shaft with an axially facing seal face, and having a seal housing mounted upon the pump housing in surrounding relationship to the drive shaft, and having an annular seal having an axial front end and an opposite facing axial rear end with the face of the front end in wiping engagement with the seal face, the improvement comprising: an annular secondary seal, having an axial front end and an opposite facing axial rear end with a face on the front end for engaging the seal face and substantially juxtaposed thereto mounted in the seal housing in concentric relationship to the first mentioned seal such that a first annular volume space is defined between the front ends of the first mentioned and secondary seals, a second annular volume space is defined between the radial outer periphery of the secondary seal and the seal housing and the rear ends of the first mentioned and secondary seals are exposed to the pressure in the second annular volume; and orifice means to fluidly interconnect the first and second annular volume spaces such that the pressure force acting on the secondary seal in the direction of the seal face increases upon failure of the primary seal due to a pressure differential between the volume spaces created by the failure and a controlled leakage emanates from the shaft seal assembly through said orifice means.