Sealing apparatus for rotating shafts, in particular stern tube seal for the propeller shafts of a ship

A stern tube seal for a rotating propeller shaft of a ship, the propeller shaft having an axial direction, said stern tube seal comprising:

• a first seal for functioning as a main seal;
• and
• a backup seal, said backup seal being for use when said first seal fails, said backup seal comprising:
• compressible sealing means for sealing out an outside medium from around the propeller shaft, the outside medium to be sealed out comprising outside water about the ship at a selected point, the outside water having a variable pressure;
• a gland member for moving in the axial direction for compressing and decompressing said compressible sealing means to vary sealing;
• a guide member for directing said gland member in the axial direction;
• an expandable body located between a portion of said gland member and a portion of said guide member, said expandable body for moving said gland member in the axial direction relative to said guide member for compressing and decompressing said compressible sealing means;
• a pressurized medium for acting upon said expandable body;
• a pressure control mechanism comprising:
• sensing means for sensing the pressure of said variable water pressure at said selected point;
• means for varying the pressure of said pressurized medium;
• and
• said pressured control mechanism for increasing and decreasing the pressurized medium directly in relation to at least the pressure of the outside water at said selected point and wherein a portion of said gland member telescopes into said guide member to form a piston-cylinder unit;
• and said expandable body is always completely contained within said piston-cylinder unit.