Marine Diesel Engine Lubrication: A critical component to avoid main engine breakdowns———Centrifugal Separators/Purifiers

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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