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