Packing ring structure

Claim 1

IN SEALING STRUCTURE: A HOUSING WALL HAVING AN OPENING THERETHROUGH, SAID HOUSING WALL HAVING A HIGH PRESSURE SIDE AND AN OPPOSITE LOW PRESSURE SIDE AND SAID OPENING INCLUDING A SHOULDER FACING SAID HIGH PRESSURE SIDE OF SAID WALL, A PISTON ROD EXTENDING THROUGH SAID OPENING, AN ANNULAR BACKUP RING POSITIONED AGAINST SAID SHOULDER, SAID BACKUP RING HAVING AN INNER CYLINDRICAL SURFACE WHICH CLOSELY SURROUNDS SAID SHAFT AND AN ANNULAR SURFACE WHICH SEALINGLY ABUTS SAID SHOULDER, SAID ANNULAR SURFACE HAVING A GENERALLY ANNULAR GROOVE THEREIN WHICH IS COMMUNICATED TO THE RADIALLY INNER SURFACE OF SAID BACKUP RING, AND AN ANNULAR PACKING RING POSITIONED AGAINST SAID BACKUP RING AND EFFECTING A SLIDING SEAL WITH SAID PISTON ROD, SAID PACKING RING AND SAID BACKUP RING HAVING ANNULAR FACES WHICH ABUT EACH OTHER, SAID ANNULAR FACE OF SAID BACKUP RING HAVING AN ANNULAR GROOVE THEREIN WHICH IS COMMUNICATED TO HIGH PRESSURE ON SAID HIGH PRESSURE SIDE OF SAID WALL TO REDUCE PRESSURE FORCES BIASING SAID PACKING RING AGAINST SAID BACKUP RING.