In case the difference of ship's draft between L.W.L and B.W.L. is not so large, it will be sufficient that the fixed oil pressure added only by the oil circulating pump in the same manner of the conventional sealing system. As example which was introduced from this point of view, the simplified AIRGUARD 3AS system is shown in Fig.13.
There is no difference to the action of the aftermost seal ring and the drain collection from the air chamber between the original AIRGUARD system and the simplified one. #3 seal ring is also preserved as the spare in both systems. But, in the simplified system, the differential pressure on #2 seal ring is variable according to the change of draft because of the fixed oil pressure.
