STERN TUBE SEAL
1.Air seal
Aft seal – 4 seal rings
Forward seal – 2 seal rings
Seal material – NBR (Nitrile
Butyl Rubber )
AFT SEAL
The AFT SEAL can be broadly divided
into the casing, which is fixed to the hull, and the chrome steel liner, which
is fixed to the propeller hub and rotates with the propeller shaft. The casing
is composed of three kinds of metal rings; flange ring, intermediate ring
and cover ring, which are tightened to each other with bolts. Four seal rings are assembled between the metal
rings with their pointed ends (lip section) touching the chrome steel liner.
The lips are pressed hard against the rotating liner and maintain a seal effect through water pressure, oil pressure, elasticity of the seal ring and tightening force of the springs. The seal rings are numbered 1, 2, 3 and 3S in order from the propeller. The #1 and #2 seal rings close out seawater, while the #1 seal ring also has the function of protecting the inside of the stern tube from foreign matter in the seawater. Lubricant oil in the stern tube is sealed in with the #3 seal ring. The #3S seal ring is a stand-by spare of the #3 seal ring. The #3S seal ring can be immediately brought into service by valve operation in engine room whenever is necessary.
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