Pressure compensated shaft seal

TLDR: In this paper, a relatively rotating face ring-type shaft seal is used for sealing the shaft bearings and lubricant chamber of a downhole drill rig, which is suitable for downhole drilling.

Abstract: Relatively-rotating face ring-type shaft seals, which are. especially suitable for sealing the shaft bearings and lubricant chamber of mud-motor-driven downhole drill rigs, have telescoped annular seal rings (123, 124) slidably mounted in a annular carrier element (122) and riding over the radial face on a face ring (112), defining a sealed intermediate chamber which may be filled with lubricant. Either the telescoped seal rings (123, 124) or the face ring (112) rotates with the bit shaft (15). Biasing means, such as a plurality of springs (143), urge the seal rings (123, 124) against the face ring (112) and pressure transmission means, such as pistons (152), mounted either in the carrier element (122) or the face ring (112) are loaded by the pressure of the ambient medium, such as drilling fluid, to maintain pressure in the intermediate chamber responsive to the pressure of the ambient medium. When the parts of the pressure transmission means exposed to ambient pressure and to intermediate chamber pressure are equal, a zero or negligible pressure differential will be maintained across the outer seal ring (124), to prevent the ambient medium from entering the outer seal ring interface. The inner seal ring (123) serves as an auxiliary back-up face ring seal for the protected bearing chamber. Since the abrasive medium does not enter the interfaces of the rings, the end faces (123', 124') of the seal rings (123, 124) riding on the face ring (112) can be reduced or narrowed to a minimum and coated with a hard facing material such as tungsten carbide.