Abstract: A normally non-contacting rotary seal is disclosed which prevents fluid from leaking from one zone, or compartment, to the next through an opening in the compartment separating wall, or bulkhead, through which a rotating shaft passes. The passage of fluid through the wall opening is prevented regardless of which side of the wall becomes flooded. An annular resilient seal, having spaced apart radial flanges, is secured around the shaft for rotation therewith in an annular chamber at the separating wall. No part of the seal normally contacts the stationary walls of the chamber. In the event one compartment becomes flooded, liquid flows past the seal flange adjacent that compartment into the chamber, forcing the other seal flange into sealing contact with the wall of the chamber to block the flow of the liquid into the adjacent compartment. In another embodiment, a stabilizing ring is mounted between the flanges.