Question 31

The Correct Answer is A. **Explanation of Option A (Correct):** A gravity feed lubricating oil system relies on potential energy (height) to deliver oil to the lubrication points (bearings). This requires a gravity tank placed above the machinery being lubricated. Since the system must be supplied from a main oil reservoir (sump) located lower down, a pump is essential to move the oil against gravity up to the tank. * **Pump Function:** The lube oil pump draws a suction on the main reservoir/sump (where the collected oil is stored) and discharges the oil to the elevated gravity tank. * **Delivery Function:** The oil in the elevated tank then flows downward via piping, utilizing gravity (hydrostatic pressure), to feed the bearings consistently and reliably. * **Return Function:** After lubricating the bearings, the spent oil must return to the lowest point in the system, which is the main reservoir/sump, via gravity drain lines, completing the cycle. Therefore, Option A accurately describes the standard components and flow path of a closed-loop gravity feed system. **Explanation of Incorrect Options:** * **Option B (Incorrect):** This describes a standard forced-feed pressure lubrication system, not a gravity feed system. In a forced-feed system, the pump discharges directly to the bearings at high pressure, and the elevated gravity tank is not used for primary supply. * **Option C (Incorrect):** This description is flawed because the pump cannot draw a suction from the gravity tank if the gravity tank is delivering the oil. The primary purpose of the pump is to *fill* the gravity tank from the lower sump, not to draw oil out of it to feed the bearings. Furthermore, the return oil must drain to the main sump, not the relatively small gravity tank. * **Option D (Incorrect):** While the pump draws from the sump, the pump does not discharge directly to the bearings in a gravity feed system (as established in B). Additionally, while the return oil does drain to the sump, it doesn't typically drain *first* to the gravity tank which then overflows. The return oil bypasses the gravity tank entirely and goes straight back to the main reservoir/sump.