Question 51 QMED03 - Oiler

The Correct Answer is B. ### Explanation for Option B (Correct) When a compressed air reservoir is placed in line with an air compressor and serves as an aftercooler, its primary function in this context is to cool the hot, saturated air discharged by the compressor. As the air cools within the reservoir, its capacity to hold water vapor decreases dramatically, causing the moisture to condense into liquid water (condensate). This liquid water accumulates at the bottom of the reservoir. To prevent corrosion of the reservoir walls, degradation of downstream components, and to maintain the quality of the compressed air, this condensed water **must be frequently drained**. Therefore, ensuring proper drainage is a critical operational requirement when the reservoir is used as an aftercooler. ### Explanation for Other Options (Incorrect) **A) It must be fitted with a sight glass.** A sight glass is typically used to monitor the level of fluids (like oil or cooling water) inside a pressurized vessel. While reservoirs have pressure gauges, a sight glass for monitoring condensed water levels is not a mandatory or standard requirement for an air reservoir acting as an aftercooler. Frequent draining (manual or automatic) is the operational necessity, regardless of visual monitoring. **C) It must be fitted with a manhole.** A manhole (or access port) is required on larger pressure vessels primarily for internal inspection and cleaning. While large reservoirs might be fitted with manholes based on size and regulatory requirements, it is not a direct operational necessity specifically because it is functioning as an aftercooler. The defining operational requirement stemming from the cooling function is water removal. **D) It must be fitted with a moisture trap at the inlet.** Moisture traps (or separators) are placed *downstream* of the cooling process (at the reservoir outlet or further down the line) to capture condensed water. Placing a moisture trap at the **inlet** would be ineffective because the water has not yet condensed; the air entering the reservoir is still hot and saturated with water vapor. The condensation process only occurs *within* the reservoir as the air cools.