a pressure gradient rotary sealing system is described with an additional configuration which uses and externally mounted pressure - reducing piston with a differential area to create a pressure differential across the system to reduce the pressure × velocity value to extend seal system life and provide early indication of impending seal failure . this invention is another embodiment of this previous invention offering using a separate externally mounted pressure reducing piston therefore the main body of the wash - pipe top - nut is lighter weight , the system has more fluid capacity , is simpler to assemble , operate and monitor and has a longer service life than previous configurations .