Question 22 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is D **Explanation for why Option D is correct:** Dry-type air filters on diesel engines function by trapping contaminants (dirt, dust) as intake air passes through the element. As the filter collects these contaminants, the flow of air becomes restricted. This restriction causes a difference in pressure between the clean side (downstream) and the dirty side (upstream) of the filter element. This difference is known as the **pressure drop** (or vacuum/restriction). As the filter loads up with dirt, the restriction increases, meaning the **pressure drop increases**. When this pressure drop exceeds a maximum limit specified by the engine or filter manufacturer, the engine is no longer receiving adequate air flow, leading to issues like power loss, increased fuel consumption, and potentially engine damage. Therefore, replacement is dictated when the pressure drop across the element increases above the specified maximum. **Explanation for why other options are incorrect:** * **A) The air filter element should be replaced when the pressure rise across the element increases above the specified maximum.** This option uses the term "pressure rise." While technically pressure is higher upstream (dirty side) than downstream (clean side), the standard industry terminology for measuring filter restriction is "pressure drop" or "vacuum." Using "pressure rise" is confusing and usually implies an unwanted increase in pressure on the outlet side, which is not the issue with a dirty filter. Furthermore, replacement is only necessary when the *restriction* (pressure drop) is high. * **B) The air filter element should be replaced when the pressure rise across the element decreases below the specified minimum.** This is incorrect. A decrease in restriction/pressure drop indicates a clean filter or, potentially, a damaged/holed filter element (which would also require replacement, but is not the primary criteria for scheduled replacement based on dirt loading). Replacement due to dirt is required when restriction is *high*. * **C) The air filter element should be replaced when the pressure drop across the element decreases below the specified minimum.** This is incorrect. A decrease in pressure drop means the filter is flowing air efficiently (cleaner). Filter replacement due to clogging is required when the pressure drop *increases* and becomes excessive.