Question 36 OSE02 - Assistant Engineer - OSV

The Correct Answer is A. **Explanation of why Option A is correct:** Dry-type air filters operate by trapping particulate matter. As the filter element collects dirt and contaminants, the resistance to airflow increases. This increased resistance is measured as the **pressure drop** (or differential pressure) across the filter element—the difference between the pressure upstream (before the filter) and the pressure downstream (after the filter). When the filter becomes sufficiently clogged, the pressure drop across it increases to a point where it significantly restricts the flow of air necessary for the engine's combustion. Restricting intake air flow negatively affects engine performance, fuel efficiency, and can lead to excessive exhaust smoke or overheating. Therefore, manufacturers specify a maximum allowable pressure drop. Once monitoring devices (like differential pressure gauges or vacuum indicators) show that the pressure drop has exceeded this specified maximum, the filter element must be replaced. **Explanation of why other options are incorrect:** * **B) The air filter element should be replaced when the pressure rise across the element decreases below the specified minimum.** This option uses confusing and incorrect terminology ("pressure rise") in the context of filter performance measurement. Furthermore, a filter requiring replacement is characterized by *high* resistance (increased pressure drop), not *low* resistance (decreased pressure drop/rise). * **C) The air filter element should be replaced when the pressure drop across the element decreases below the specified minimum.** A low pressure drop indicates that the filter is clean or brand new, offering minimal resistance to airflow. Replacing a filter because the pressure drop is *low* is wasteful and unnecessary, as the criteria for replacement is high restriction (high pressure drop). * **D) The air filter element should be replaced when the pressure rise across the element increases above the specified maximum.** Similar to option B, "pressure rise" is not the standard term used to measure restriction (it is usually "pressure drop" or "vacuum/depression"). While a restrictive filter does involve an increase in resistance, the standard accepted terminology and measurement is based on the *drop* in pressure from the inlet to the outlet, making the use of "pressure rise" technically inaccurate in this context.