US Patent 7435052 Shaft oil purge system

A shaft oil purge system comprises an entrance seal, an exit seal and a buffer air flow. The entrance seal comprises a circumferential carbon seal running on an inner shaft and another carbon seal running on an outer shaft. The exit seal comprises a labyrinth seal positioned on the inner shaft and towards the exit end of the annulus between the shafts. An abradable material filled groove positioned radially outward from the exit seal allows the inner shaft to rub without compromising the integrity of the outer shaft. The buffer air flow enters the annulus from a cavity at the entrance seal, purges oil from the annulus and improves the efficiency of the seals.