Centrifugal separators, also known as purifiers, tend
to be installed on vessels where the sump capacity of the engine is greater than
750 litres.
In addition to removing water, separators also extract
solid and soluble impurities provided that the specific gravity of such
impurities is higher than the specific gravity of the separated oil. Lubricating
oil must be at the correct temperature in order for the separation process to be
effective, usually 85-95°C.
The separation process becomes more efficient towards
the upper end of this range. A gravity disc controls the extraction of water and
it is essential that the disc is the correct size. Separators must also be run
at their maximum design speed.
The flow rate should be kept at a minimum (equipment
manufacturers generally recommend a flow rate of around 20% of the separator’s
rated capacity), and all lubricating oil in the system should be circulated
approximately 4 to 5 times every 24 hours.
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Lubricating oil purifiers extract solid and soluble
impurities
Separators should not be taken out of service when the
main engine is stopped unless repairs are required or if the vessel will be idle
for a long period. In such an event they must be reactivated well before any
attempt is made to restart the engine.
Leakage of heavy fuel into the lubricating oil system
will make the lubricating oil more viscous. Conversely, diesel fuel unlike heavy
fuel reduces the viscosity of lubricating oil. Separators may purify heavy fuel
from lubricating oil. However, purification will not separate diesel fuel from
lubricating oil as their densities are similar. In practice the viscosity of
lubricating oil cannot be restored effectively unless a partial or complete oil
change is carried out.
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