Question 25 AEL01 - Assistant Engineer - Limited

The Correct Answer is D ### Why Option D ("metal disks") is Correct The most common type of full-flow, high-pressure lube oil element used to protect reduction gears and main bearings in large/mid-size diesel applications is the **metal disk** strainer, often referred to as an edge-type or stacked-disk strainer (e.g., Cuno-style). 1. **Principle of Operation:** These elements consist of a stack of very thin, uniformly manufactured metal disks separated by precision spacers. The oil is forced to flow between the disks (the edge), trapping contaminants larger than the specified gap. 2. **Durability and Precision:** Metal disks are extremely rugged, resistant to high temperatures and pressures, and provide a very precise micron rating suitable for bearing protection. 3. **Cleanability:** Crucially, these elements are designed to be cleanable and often *self-cleaning*. By rotating the stack of disks against a fixed scraper blade, trapped particulates are scraped off and flushed away (backflushed) while the engine is running, making them ideal for continuous, critical operations. ### Why the Other Options Are Incorrect **A) pleated paper:** Pleated paper elements are disposable *filters* (not strainers in the traditional sense) typically used in bypass filtration or for very fine particulate removal in non-critical auxiliary systems. They have limited dirt-holding capacity, are not back-flushable, and would quickly clog or tear under the full flow requirements of a large reduction gear's primary lube system. **B) wire mesh:** Simple wire mesh elements (woven screens) are often used for suction strainers or coarse filtration, but they generally lack the precision and robust, automated self-cleaning features required for the full-flow pressure strainer protecting critical reduction gear bearings. While they are metallic, the stacked-disk configuration (D) offers superior performance for this specific application. **C) fibrous braid:** Fibrous elements (like depth cartridges made of cotton or synthetic fibers) are disposable depth *filters*. They are not suitable for primary, full-flow straining because they cannot be cleaned or backflushed and have a finite operational life before requiring replacement.