Question 13 3AE01 - Third Assistant Engineer

The Correct Answer is C ### Why Option C (crankcase pressure) is correct: The space below the cylinder liner's lower seals (often referred to as the liner skirt space or weep hole drainage area) is designed to act as an indicator and containment zone. This space separates the cooling water jacket (above the lower seals) and the main engine crankcase (below this space). If the lower seals fail, the cooling water (or sometimes lube oil depending on the specific engine design of the lower seal arrangement) will leak out through "weep holes" into a collection space, preventing the fluid from contaminating the main crankcase lube oil system. This collection space itself is open and vented directly to the atmosphere or, more commonly in large marine or industrial diesel engines, vented into the *crankcase atmosphere*. Therefore, the pressure acting on this space is the ambient pressure inside the crankcase, which is normally atmospheric pressure or slightly below (vacuum) due to ventilation, but is generally referred to as **crankcase pressure**. ### Why the other options are incorrect: **A) Lube oil pressure:** While lube oil might circulate near the liner skirt for lubrication, the specific space *below the lower cooling water seals* is not pressurized by the main high-pressure lube oil system. The lube oil present here is generally splash lubrication or drainage, not under system pressure. **B) Cooling water pressure:** The space *above* the lower seals (the water jacket) is subjected to cooling water pressure. The space *below* the seals is designed to be a buffer zone precisely to prevent pressurized cooling water from entering the crankcase if the seals fail. **D) Scavenge air pressure:** Scavenge air pressure (in two-stroke engines) is contained within the scavenge box, which is located above the lower part of the cylinder liner and separated from the crankcase by the stuffing box (in crosshead engines) or the crankcase itself (in trunk piston engines). This pressure does not directly act upon the weep hole drainage space below the cooling water seals.