Two supply pumps take suction from the heavy fuel oil servicetanks or from the diesel oil service tank through an adjustable 3-way mixing valve. The supply line from each service tank isequipped with none-return valves in order to prevent confluence.The supply pumps discharge to the venting tank at a pressure ofapprox. 4 bar(g). The total amount of fuel oil supplied to theventing tank. is measured by a flow meter (totalise) equipped witha by-pass valve.