Question 24 OSE02 - Assistant Engineer - OSV

The Correct Answer is D **Explanation of why option D is correct:** Option D, "Periodically opening, then reclosing, the drain valve on coalescing type diesel oil filters," represents the primary and most effective maintenance practice for preventing moisture carryover to the sensitive fuel injection system. 1. **Function of Coalescing Filters:** Coalescing filters are specifically designed to separate small water droplets from the fuel. They cause these tiny droplets to merge (coalesce) into larger drops. Because water is denser than diesel fuel, these larger drops settle to the bottom of the filter housing or sump. 2. **Importance of Draining:** If the accumulated water at the bottom of the filter housing is not drained regularly, the sump will fill up. Once the sump is full, the water level can rise to the point where it is re-entrained (picked up) by the flowing fuel and carried downstream toward the injection pumps and nozzles. 3. **Best Protection:** Therefore, periodic draining (opening, then reclosing the drain valve) is the essential, active maintenance step that removes the separated water, ensuring the filter remains effective and providing the best protection against moisture carryover. **Explanation of why the other options are incorrect:** * **A) Closing the diesel oil day tank vents, particularly when the relative humidity is high:** This practice is incorrect and potentially dangerous. Day tank vents must remain open to equalize pressure as fuel is consumed and to prevent a vacuum or pressure buildup. While humidity control is important for long-term storage, closing the vents is not a viable or safe practice for operational tanks and does not directly address water separated by the primary filtration system. * **B) Periodically opening, then reclosing, the vent valve on coalescing type diesel oil filters:** The vent valve on a filter housing is used to release air or trapped vapor during initial filling or maintenance to prevent airlocks. It is not used to remove water, which settles at the bottom. Using the vent for water removal would be inefficient and hazardous, potentially spraying fuel/water mixture. * **C) Frequently replacing fuel injection pump and injector nozzle inlet fuel filters:** While frequent filter replacement is generally good for particle cleanliness, it is a reactive measure for contamination, not a proactive defense against water ingress. If the primary coalescing filter (which handles the bulk of the water removal) fails due to lack of draining, the smaller downstream filters may be overwhelmed and damaged. Draining the water (Option D) is the necessary proactive step to maintain the integrity of the entire filtration system.