The radial force loaded on the aftermost seal ring should be usually reduced. When seal rings are operated under the stable condition which has a constant and small differential pressure in spite of the change of sea water pressure, those shows better sealing performance. The second concept is led to control the pressure in the seal, due to supply the compressed air having a constant flow rate and blow it into the sea water through under the lip of seal ring.
In case that the seal ring has unfortunately some damages and the sea water infiltrated or the oil leaked to the air chamber, it must be exhaustively collected to inboard. The third concept is achieved to collect the drain automatically inboard through the drain piping line connected to the drain collection unit.
2.2 Structure of aft seal
The structure of aft seal of AIRGUARD 3AS sealing system is shown in Fig.2. AIRGUARD 3AS has three seal rings that one is directed to the sea water and two are to the stern tube. The chamber between #1 and #2 seal rings is an air chamber and filled with the compressed air supplied from inboard. The air always blows under the lip of #1 seal ring to the sea water.
