Question 37 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is C ### 2. Explanation of why Option C is correct: **C) Mechanically poke through the drain openings with a rod to clear the drains.** Air box drains on large two-stroke engines typically become blocked due to the accumulation of hard carbon deposits, solidified oil sludge, and fibrous materials mixing with water vapor. These blockages are mechanical and solid in nature. 1. **Standard Procedure:** Mechanical poking (using a specially designed ‘poking rod’ or drain wire) is the standard and necessary maintenance procedure for clearing these hard, solidified blockages from the small drain orifices and piping. 2. **Effectiveness:** Since the obstruction is solid gunk, no amount of pressure (either existing air box pressure or reverse air pressure) will reliably clear it. Only direct mechanical action can break up and dislodge the material blocking the flow path. 3. **Safety:** This method is safe, as it does not involve potentially dangerous pressure manipulations or contamination of engine systems. ### 3. Explanation of why the other options are incorrect: **A) Increase the crankcase pressure to blow the air box drain openings clear.** * **Incorrect System:** Air box drains lead to an external drain tank, not the engine crankcase. * **Safety Hazard:** Crankcase pressure is usually maintained near atmospheric or slightly negative. Intentionally increasing crankcase pressure is highly dangerous, risking explosion, oil mist release, and severe personnel injury. **B) Blow through the drain openings with compressed air to clear the drains.** * **Ineffective and Counterproductive:** While compressed air might seem useful, if the blockage is solid carbon (the typical culprit), high-pressure air may not clear it. Furthermore, if the engine is running or recently stopped, blowing air *into* the drain line could force sludge and accumulated oil backward into the air box, contaminating the scavenge space and potentially increasing the risk of a scavenge fire. Mechanical cleaning (poking) is safer and more direct. **D) Increase the air box pressure to blow the air box drain openings clear.** * **Ineffective:** The air box is already under significant pressure (scavenge pressure, typically 1.5–3.0 bar above atmospheric). If this existing pressure—which is the force attempting to push the drainage out—cannot clear the obstruction, increasing the pressure (by increasing engine load) will not solve the problem because the obstruction is a mechanical solid, not a fluid blockage. The engine load is an operational factor, not a tool for clearing mechanical clogs.