A deep tank in the engine room used for pre-cleaning of fuel oils by gravity; a liquid mixture in the settling tank clears slowly as a heavier liquid and solids sink to the bottom under influence of gravity.
Usually there are two settling tanks, each with a capacity sufficient for 24 hours full load operation of all consumers. Tanks should be designed to provide the most efficient sludge and water separation. Each settling tank should be provided with baffles to reduce mixing of sludge with the fuel. The bottom of the tank should be with slope toward the sludge drains, and pump suction shall be not in the vicinity of the sludge space. The temerature in fuel settling tanks should be as high as possible to help the dirt to settle. However, the temperature should be below 75°C in order to avoid the formation of asphaltenes, and min 7°C above the pour point of the fuel to ensure pumpability.