environmental protection

Bio Oils

Further steps to protect the environment have involved the introduction of Bio Oils.  These oils work well when used in conjunction with airspace type seals.  However in a sealing system where the sea water can be transferred into the sterntube oil, i.e. a typical three ring system, there is a danger that the bio oil in conjunction with sea water will start to attack the material of the sealing ring leading to early failure of the seal.  Different bio oils are more or less aggressive towards the seal rings material when sea water is present in the system, and care must be taken to ensure that only bio oils, which are approved for that particular application, are used.   

All seals whether face type or lip type require a certain transfer of liquid across the sealing point in order to cool and lubricate the seal.  

SC2000 airspace seal

As a result new designs were developed with an airspace chamber between the water seals and the oil seals.  The liquid passing both sets of seals accumulate in this airspace chamber which can then be emptied by the use of compressed air transporting the mix of water and oil back into a collecting tank on board the vessel.  Provided that the mix of water and oil is pumped back into the vessel and not into the seawater (which is what happens with some designs), such seals ensure that there is absolutely no transfer whatsoever in normal operation.