Question 20 OSE01 - Chief Engineer - OSV

The Correct Answer is D ### 1. Explanation of why Option D is Correct The problem establishes that the baseline (clean, properly sealing) restriction for the air intake filter, measured between the filter and the turbocharger blower inlet (where the vacuum is highest), is $10"$ of water column (negative). This restriction measurement is a differential pressure (or vacuum) caused by the resistance the air encounters as it is pulled through the filter element. * **Filter Element Restricted with Dust:** When a filter element becomes clogged with dust, its ability to allow air to pass through diminishes. This increased resistance causes the turbocharger (which is still trying to pull the same volume of air at full load) to generate a **higher vacuum** (more negative pressure) in the duct. Therefore, a reading *greater* than $10"$ W.C. (e.g., $15"$ W.C.) indicates that the filter is restricted. * **Filter Element Being Bypassed Due to an Improper Seal:** If the filter element is poorly sealed, some air will bypass the actual filter media and enter the intake duct directly through the gaps. Since the bypass path offers little to no resistance, the total resistance to airflow is reduced. This reduction in resistance causes the turbocharger to generate a **lower vacuum** (less negative pressure) in the duct. Therefore, a reading *less* than $10"$ W.C. (e.g., $5"$ W.C.) indicates that the filter is being bypassed. Option D correctly matches the increased restriction (dust) with a higher negative reading ($15"$ W.C.) and the decreased restriction (bypass) with a lower negative reading ($5"$ W.C.). ### 2. Explanation of why the Other Options are Incorrect **A) A reading of 5" of water column (negative) could indicate that the filter element is restricted with dust or that the filter element is being bypassed due to an improper seal. Either condition is equally likely to result in this reading.** * **Incorrect:** A reading of $5"$ W.C. is *less* than the normal $10"$ W.C. Clean restriction. This indicates a *decrease* in resistance, which is caused by a bypass (improper seal), not an *increase* in resistance (dust restriction). **B) A reading of 15" of water column (negative) could indicate that the filter element is restricted with dust or that the filter element is being bypassed due to an improper seal. Either condition is equally likely to result in this reading.** * **Incorrect:** A reading of $15"$ W.C. is *greater* than the normal $10"$ W.C. Clean restriction. This indicates an *increase* in resistance, which is caused by dust restriction, not a bypass (which would decrease resistance). **C) A reading of 5" of water column (negative) indicates that the filter element is restricted with dust, and a reading of 15" of water column (negative) indicates that the filter element is being bypassed due to an improper seal.** * **Incorrect:** This option reverses the causes and effects. $5"$ W.C. (lower vacuum/less restriction) indicates a bypass, not restriction. $15"$ W.C. (higher vacuum/more restriction) indicates dust restriction, not a bypass.