Also a small amount of the air usually blows to inboard through the drain collection line. The chamber between #2 and #3 seal rings and stern tube are filled with the oil circlulated by the pump. The oil into the oil chamber between #2 and #3 seal rings is returned to the stern tube through under the lip of #3 seal ring.
To cope with the current increase of troubles caused by fishnets floating on the sea, P-ring (UNNET fishnet protector) is provided as a standard component and prevents the seal from fishnets caught in.
The structure of AIRGUARD 3AS is simple and similar to the conventional type having three seal rings, except of the direction of #2 seal ring. As the dimensions for installation of the both seal assembies are completely same, there is no problem to equip AIRGUARD 3AS instead of the conventional seal.
2.3 Arrangement of the system
The outline of AIRGUARD 3AS sealing system is shown in Fig.3. The equipments installed inboard are basically consisted of an air control unit, a drain collection unit, a L.O. tank unit and a L.O. pump unit.
The air control unit includes air filters, pressure regulators, flow controllers, flow meters, air relays, pressure switch and others. Taking into consideration of the reliability of the system, main components are assembled to be doubled, and if necessary, dual lines can be changed over. The unit supplies a compressed air to the top part of the air chamber between #1 and #2 seal rings through the piping, and also to the top of the L.O. tank. The flow controller controls the amount of air to the air chamber to keep a constant rate at any time. The air from the air relay, which is activated by the air pressure supplied to the air chamber, works to pressurize the oil in the L.O. tank, so as to the oil pressures between #2 and #3 seal rings and in stern tube are always kept higher than the air pressure.
The drain collection unit has a automatic drain collector, needle valves, a line filter, and so on. The drain collection piping is connected with the bottom of the air chamber. In normal condition, most of the compressed air blows out from the air chamber to the sea water through under the aftermost seal ring, and the rest of the air flows out the needle valve of the collection unit. When the oil or sea water leaks into the air chamber, it is pressed downward by the air pressure, collected through the piping at the bottom of the air chamber to the drain collection unit, and automatically discharged inboard.
The L.O. tank unit is made up by a pressurized tank, a safety valve, a level switch,
