Question 1 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is D. **Explanation for Option D (Correct):** When a compressed air reservoir (receiver) is used as an aftercooler, its primary function is to cool the hot, saturated air discharged from the compressor. As the air cools within the reservoir, its ability to hold water vapor decreases significantly. This cooling process causes a large amount of water vapor to condense into liquid water (condensate). If this water is not removed, it reduces the effective storage volume of the reservoir, promotes corrosion, and can be carried downstream into the air system, damaging tools and equipment. Therefore, the reservoir **must be frequently drained of condensed water** to maintain system efficiency and integrity. **Explanation for Incorrect Options:** * **A) It must be fitted with a manhole:** While large pressure vessels often require manholes for inspection and maintenance, compressed air reservoirs used specifically with smaller industrial compressors (where aftercooling is a primary function) may or may not be large enough to necessitate a manhole. Manholes are required by certain codes based on size, but draining condensate (D) is a universal operational necessity directly resulting from its use as an aftercooler. * **B) It must be fitted with a sight glass:** A sight glass allows visualization of the liquid level inside the tank. While useful for monitoring the liquid level (such as lubricating oil or water), it is not a mandatory or fundamental requirement for the basic operation and safety of a compressed air receiver used as an aftercooler. Frequent draining (D) is the required action; a sight glass is merely an accessory for monitoring. * **C) It must be fitted with a moisture trap at the inlet:** Moisture traps (or separators) are typically placed *after* the cooling process (at the outlet or downstream) to capture condensed water. Placing a trap at the *inlet* would be ineffective because the air entering the reservoir is hot and saturated, meaning the water is still largely in vapor form and has not yet condensed. The condensation happens *inside* the reservoir as the air cools.