Dual non-contacting mechanical face seal having concentric seal faces

A mechanical face seal for providing fluid seal between a housing and a rotatable shaft, the housing being exposed to a process fluid, said seal comprising

• a first seal ring having a first seal face extending between an outer surface of said first seal ring and an inner surface of said first seal ring,
• a second seal ring having a second seal face, said first and second seal faces being opposed to one another,
• one of said first seal ring and said second seal ring being adapted to rotate with said rotatable shaft, the other of said first seal ring and said second seal ring being restrained from rotating,
• a plurality of pumping grooves formed in said first seal face, said plurality of pumping grooves receiving a barrier fluid distinct from said process fluid introduced to said first and said second seal faces, said plurality of pumping grooves generating a pressure field between said first and second seal faces to separate said seal faces during periods of shaft rotation, said plurality of pumping grooves being positioned between said outer surface and said inner surface of said first seal ring to form two concentric seal faces on said first seal face, and said second seal face being dimensioned to seat over said grooves and at least a portion of said two concentric seal faces when assembled,
• a closing fluid network to introduce a closing fluid to a rear surface of said second seal ring to provide a closing force on said second seal ring, said closing force acting upon a portion said second seal face overlapping said first portion of said first seal face but not upon a portion of said second seal face overlapping said second portion of said first seal face to offset said pressure field.