The purpose of the interlocked three-way valve shown in the illustration is to __________. Illustration MO-0058

Correct Answer: Option D — change fuel from heavy to light oil or vice versa while insuring that oil is returned to the proper day tank

Interlocked three-way changeover valves in marine fuel systems allow safe transitions between heavy fuel oil and marine diesel oil while simultaneously directing return flow to the appropriate day tank, preventing heavy fuel contamination of light fuel service tanks.