All types of seal require a small amount of liquid to migrate under the sealing surface in order to provide the lubrication and cooling which is required to prevent the sealing surface from overheating. The lubrication effect is reduced when water enters the oil, but in the past this has not caused operational problems with lip type seals unless there was a severe leakage. However, when bio oils / EALs are used even small amounts of water can dramatically affect the performance of the seal. The reason for this is the hydrolysis which takes place when water mixes with bio oils, resulting in the creation of acids which attack the seal material. Nearly all Viton seals on the market today are susceptible to this form of acid attack and unless the seal manufacturer specifies otherwise it is important to control the water content in the oil. SKF Marine GmbH has developed a special oil dryer unit to extract water from the oil in the aft seal.
The unit can be operated 24 hours per day and under normal operating conditions the aft seal lube oil will be kept completely free of water. The unit is designed to extract up to 1.5 litres per day, and will extract water even from emulsified or dissolved water. Even when it is not required to control the water content in the aft seal oil chamber, operation of the oil dryer removal of the water will reduce wear and increase the life of the seal. Likewise the sterntube bearings are provided with additional protection against wear and damage.
The plug and play solution is delivered as a complete system including aft seal tank, oil circulating pump, filter and control panel. The unit is supplied fully assembled and tested, ready for immediate and easy installation by the shipyard. Only an air supply on board is required.
A self-explanatory control unit makes it easy to handle the water evaporation and oil circulation. The integrated fail-safe system for pump and heater avoids any danger from electricity or air supply break down.
– extremes of trim position
– high shaft vibrations
– shaft or bush misalignment
– too much clearance or wear in sterntube bushes
– high axial shaft clearance
– unfavourable water turbulence through the propeller