Question 54 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is C ### Why Option C is Correct: A **gravity feed lubricating oil system** relies on potential energy (height) to deliver oil to the machinery (bearings). For this to work, a constant supply of oil must be maintained above the machinery. 1. **Pump Function (Charging):** The system must first move the oil from the lowest point (the **lube oil reservoir/sump**) up to the highest point (the **lube oil gravity tank**). Therefore, the pump draws suction from the sump and discharges to the gravity tank. 2. **Delivery (Gravity Feed):** Once in the gravity tank, the oil uses gravity to flow down through the piping and lubricate the bearings. 3. **Return (Collection):** After passing through the bearings, the used oil naturally flows back down to the lowest point of the system—the **lube oil reservoir/sump**—to be filtered, cooled, and reused. This sequence perfectly describes the function listed in Option C: "The lube oil pump draws a suction on the lube oil reservoir/sump and discharges to the lube oil gravity tank. The oil then gravity-feeds the bearings and the return oil drains to the lube oil reservoir/sump." ### Why Other Options Are Incorrect: **A) The lube oil pump draws a suction on the lube oil reservoir/sump and discharges directly to the bearings. The return oil then gravity drains to the lube oil gravity tank which overflows to the lube oil reservoir/sump.** * **Incorrect Delivery:** If the pump discharges *directly* to the bearings, the system is pump-pressurized (forced lubrication), not gravity-fed. * **Incorrect Return:** Return oil drains to the lowest point (the sump), not the highest point (the gravity tank). This configuration makes no logical sense for oil circulation. **B) The lube oil pump draws a suction on the lube oil gravity tank and discharges directly to the bearings. The return oil then gravity drains to the lube oil gravity tank.** * **Incorrect Pump Suction:** Drawing suction from the gravity tank means the pump is pulling oil that is already high up and is meant to be delivered by gravity. The pump should be filling the gravity tank, not draining it. * **Incorrect Return:** The return oil must drain to the main sump for cooling and filtration, not back into the gravity tank (unless it's just a small local header, which contradicts the overall system logic). **D) The lube oil pump draws a suction on the lube oil reservoir/sump and discharges directly to the bearings. The return oil then gravity-drains to the lube oil reservoir/sump.** * **Incorrect System Type:** This describes a standard **forced lubrication** (pump-pressurized) system where the pump provides the pressure necessary for delivery, not a **gravity feed** system which requires the gravity tank for delivery pressure.