changed by adjusting the bias pressure on the air relay. After all, the differential pressures on every seal rings are controlled to be constant in AIRGUARD aft seal.
But, in case of conventional seal, the differential pressures on the seal rings in aft seal are forced to change according to the sea water pressure (L.W.L. ─ B.W.L.).
2.6 Main features of the system
Main features of AIRDUARD 3AS sealing system are summarized as follows.
1) Advanced pollution free
─ The sea water and oil is completely isolated by arranging the air chamber and ejecting the air from air barrier under the aftermost seal ring.
─ If any spilling of the sea water or oil occurs into air chamber, it is collected automatically with the drain collection unit to prevent from the leakage.
2) Operation free
─ Once the air flow rate and oil pressure are set up with the flow controller and air relay at the time of installation, a manual adjustment is not necessary later.
Usually, only the periodic watch is enough to confirm the operating conditions.
─ The air and oil pressures are automatically controlled following to the change of draft, and the differential pressures on every seal rings are always kept constant in aft seal.
3) Service life extension
─ The loads on each seal ring is constant and lower than the conventonal types, so seal rings are operated under the stable condition.
─ As the aftermost seal ring is used under the floating condition by the air flow, the damage caused by water lubrication is avoidable.
─ Other seal rings are also operated under the desirable condition like as forward seal without contact of the sea water.
─ With fitting P-ring (UNNET fishnet protector) as the standard component, the seal rings are protected against winding of fishing nets and rope.
4) Others
─ #3 seal ring is prepared as the spare in ordinary operation.
If a lot of oil leakage through #2 seal ring happened, #3 seal ring is quickly set in service.
─ As the air consumption (30-40 Liter/min ANR) is so small, there is no affect on such as air compressors or air vessels in engine room and no need to increase the capacity.
─ The piping system is simplified and the hand-operating is unnecessary to change the stern tube oil pressure in accodance with the draft condition on larger ships.
