Shaft seal with fluid pressure and spring bias

Claim 1

A shaft seal comprising a mechanical seal in combination with packing which is maintained under substantially constant compression within an annular space formed by the shaft and the interior wall of a stuffing box mounted concentrically with respect to said shaft, said packing being located within said annular space at a position along the shaft closest to the process stream end of the shaft, said mechanical seal being located at a position along the shaft further away from the process stream end of the shaft than the packing thereby forming an annular cavity bounded by the shaft, the interior wall of the stuffing box, the packing and the mechanical seal, a means for providing a fluid under pressure to said cavity, the material of construction, configuration and compression to the packing being such that when said fluid is provided to said cavity under pressure greater than the pressure of the process stream, the fluid will flow through the packing into the process stream with sufficient velocity to prevent process fluid from entering the stuffing box and with insufficient volume rate of flow to cause significant dilution of the process fluid, wherein the packing is maintained under substantially constant compression by means of at least one coil spring exerting a force thereon of approximately 10-100 pounds.