22. State about stern tube sealing with aft simplex shaft seal type.

1- Cover ring

2- Sealing ring (No.1, 2, 3, 3S)

3- Inter mediate rings

4- Oil inlet

5- Flange ring

6- Packing

7- Stern tube

8- Stern frame

9- “O” ring

10- Aft chrome steel liner

Function:

          To prevent sea water penetrates to the engine room and leakage of oil from the stern tube.

Structure

-The aft seal is composed of the casing fixed to the hull and the liner, which is fixed to the propeller boss and rotates with the propeller shaft together.

-The casing consists of three kinds of metal rings (flange ring, intermediate rings and cover ring), which are separately tightened with bolts.

-Individually assembled between these rings, four sealing rings are composed the leading edge (lips) touching the liner. These lips are pressed hard against the rotating liner by the water and oil pressure, elasticity of the rubber material and the tightening force of the springs to maintain sealing effect.

-The four sealing rings are numbered by No.1, No.2, No.3, and No.3S from the seawater side. Seawater penetration is tightly protected by No.1 and No.2 sealing rings.

-No.1 sealing ring, in particular, has an additional function to protect the inside of the stern tube from extraneous substances in seawater

-The oil pressure in the chamber between two (No.3 and No.3S) sealing rings located at forward is usually adjusted to be the same pressure as stern tube pressure, which is 0.2 - 0.3 kg/cm2 higher than sea water pressure. Therefore, there is no pressure loaded on No.3S sealing ring on the above conditions. Normally, lubricating oil in the stern tube is sealed by No.3 sealing ring.

-However, if much oil leakage from No.3 and No.3S chamber would be found, No.3S sealing ring could be used to protect the above leakage instead of No.3 sealing ring by the easy valve operation handle inboard.