Open systems using gravity tanks, etc., are rarely met nowadays and Figure 1.8 shows a characteristic arrangement of pressure tanks, calorifiers and pumps for a large ship. The fresh water pumps are self-priming, drawing from storage tanks and discharging through filters to a rising main, branched to give a cold supply and a hot supply in closed circuit through a calorifier. A tank kept under pressure by an external supply of compressed air rests on the system and provides the head necessary
In motorships the oil, after passing through main and motion bearings and oil-cooled pistons, etc., is either retained in the bedplate or flows by gravity to a sump tank. In either case, the oil pumps, which may be selfpriming, submerged centrifugal or rotary positive displacement, draw the oil through magnetic strainers and discharge to: filters - oil coolers - engine lubricating and/or cooling manifolds