Question 172Motor Plants - QMED

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According to the illustrated diesel engine fuel treatment and fuel service systems schematic, what statement is true concerning the valves labeled "4" and "5"? Illustration MO-0077

Diagram for USCG Motor Plants QMED: According to the illustrated diesel engine fuel treatment and fuel service...
AValves 4 and 5 are closed during normal operation, but when opened will allow one of the HFO purifiers to be used as a backup DO purifier, should the DO purifier become disabled.
BValves 4 and 5 are closed during normal operation, but when opened will allow the DO purifier to be used as a backup HFO purifier, should one of the HFO purifiers become disabled.
CValves 4 and 5 are closed during normal operation, but when opened will allow all three purifiers to centrifuge HFO while in series.
DValves 4 and 5 are closed during normal operation, but when opened will allow all three purifiers to centrifuge HFO while in parallel.
AI Explanation

The correct answer is A. Valves 4 and 5 are closed during normal operation, but when opened, they will allow one of the HFO (heavy fuel oil) purifiers to be used as a backup DO (diesel oil) purifier, should the primary DO purifier become disabled. This allows the system to maintain diesel oil purification if the main DO purifier fails. The other options are incorrect because they do not accurately describe the function of valves 4 and 5 in the fuel treatment and fuel service systems schematic. Option B is incorrect because the valves do not allow the DO purifier to be used as a backup for the HFO purifiers. Options C and D are incorrect because the valves do not allow all three purifiers to be used in series or parallel for HFO purification.

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Official Resources
46 CFR Machinery & Electrical 46 CFR Engineering USCG National Maritime Center
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