🔍 Key Concepts

• Trace the fuel flow paths from the HFO settling tanks and DO settling tank through their respective purifiers and into the day/mixing tanks. • Understand how normally-closed cross-connection valves (like 4 and 5) can let one system back up the other when opened. • Consider typical practice on ships having two HFO purifiers and one DO purifier, and which purifier is more likely to be used as a backup for the other.

💭 Think About

• If valves 4 and 5 are opened together, from which tank would the DO purifier be able to take suction, and to which tank or header would it discharge? • Looking at the arrows on the diagram, do valves 4 and 5 place the three purifiers in a straight line (series), or do they just allow another purifier to connect to a different supply/discharge (backup use)? • Based on the piping shown, does opening 4 and 5 move heavy fuel through the DO purifier, or distillate fuel through one of the HFO purifiers?

✅ Before You Answer

• Follow the pipe connected to valve 5 and confirm exactly which tanks’ outlet header it ties together when opened. • Follow the pipe connected to valve 4 and see whether it joins the discharge of the DO purifier to the HFO purifier discharge line or vice versa. • Verify whether there is any piping that would make all three purifiers share both a common inlet and a common outlet (required for true parallel or series operation).