According to the illustrated diesel engine fuel treatment and fuel service systems schematic, what would be the appropriate valve configuration for operating the two heavy fuel oil purifiers in series? Illustration MO-0077

Correct Answer: Option D — Valves 2 and 3 CLOSED, and Valve 6 OPEN

Configuring heavy fuel oil purifiers in series requires isolating parallel paths by closing valves 2 and 3 while opening valve 6 to establish sequential dual-stage purification. This ensures complete contaminant removal before the fuel reaches service tanks.