Question 30 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is A **Why option A is correct:** Dry-type air filters operate by allowing air to pass through a fibrous or pleated element. As the filter captures contaminants (dirt, dust, soot), the pores in the filter media become clogged. This clogging increases the resistance to airflow. The difference in pressure between the upstream side (dirty air) and the downstream side (clean air) of the filter is known as the **pressure drop** (or differential pressure). As the filter loads up with dirt, the pressure drop across the element increases. Once this pressure drop exceeds a maximum limit specified by the engine manufacturer, it indicates that the engine is struggling to draw enough air for proper combustion, leading to reduced performance, potential turbocharger damage, and higher fuel consumption. Therefore, filter replacement is necessary when the pressure drop increases above the specified maximum. **Why the other options are incorrect:** * **B) 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 the pressure difference increases, the standard and correct terminology used for filters indicating increased resistance is **pressure drop** or **differential pressure**. In airflow systems, you measure the *drop* in pressure from inlet to outlet caused by the restriction. * **C) The air filter element should be replaced when the pressure rise across the element decreases below the specified minimum.** A decrease in resistance (or pressure drop) would indicate that the filter is either clean, incorrectly installed, or potentially ruptured, allowing unfiltered air to pass. Replacement is necessary when resistance *increases*, not decreases. * **D) The air filter element should be replaced when the pressure drop across the element decreases below the specified minimum.** A decrease in pressure drop means the filter is flowing air too freely (low restriction). A dirty, clogged filter causes the pressure drop to *increase* (high restriction), which is the standard trigger for replacement.