🔍 Key Concepts

• Fuel oil system flow paths between the HFO day tank, mixing tank, and main engine • Role of the mixing tank in handling return fuel and possible overflow paths • How viscosity control is actually achieved in this system (note viscometer location and valve 7, not valve 1)

💭 Think About

• Trace the piping connected to valve '1' on the diagram. Where does fuel go if valve 1 is open, and what tank or component does it interact with? • Compare the function of valve 1 with valve 7 near the final heaters and viscometer. Which valve seems linked to viscosity control, and which to tank level/recirculation? • Ask yourself: in which one of the listed operating conditions would you need to change where excess or circulating fuel is sent from the mixing tank?

✅ Before You Answer

• Confirm exactly which tank or component valve 1 connects the mixing tank to on the illustration. • Verify what happens to the mixing tank level if all return fuel keeps circulating and valve 1 remains shut for a long period. • Check that viscosity adjustments in this system are made by the viscometer acting on valve 7 (around the final heaters), not by valve 1, so eliminate any answers that confuse these functions.