Aft sealing assembly for stern tubes

Claim 1

A sealing assembly for effecting a seal adjacent the stern tube oil chamber around the tail shaft of a ship wherein there is means for maintaining the oil in said chamber under a pressure slightly greater than sea water pressure at the level of the tail shaft, said assembly including an annular casing having an annular cavity within which axially spaced annular lip seals are supported to provide an annular pocket therebetween, one of which seals has a face exposed to the pressure of oil in said stern tube chamber, the improvement comprising valve-controlled communication between said annular pocket and said oil chamber, and including a valve of a type which is actuated by the pressure difference between the pressure in said annular pocket and the pressure in said stern tube oil chamber, said valve having a spring-urged valve stem normally maintaining the valve closed, said valve being so disposed and its spring having such rating that the valve is automatically opened when the pressure in the liquid chamber exceeds the pressure in the annular pocket by a predetermined amount equal to the force exerted by the valve spring.