Which of the listed order of valves represents the proper installation of the main feed water supply line to a marine propulsion boiler?

Correct Answer: Option D — Stop-check, regulator, stop

Proper piping configuration places the stop-check valve closest to the boiler to prevent backflow, followed by the feed water regulator for flow control, and a manual stop valve upstream for complete system isolation, satisfying Title 46 CFR marine engineering standards.