Question 22 QMED01 - Junior Engineer

The Correct Answer is D **Explanation for Option D (Sufficient oil flow is being supplied to the gravity tank.):** A lube oil gravity tank is designed to provide a reliable backup supply of lubricating oil (often for a turbine or critical machinery) in case the main oil pump fails. It is continuously filled by the main oil pump during normal operation. The gravity tank overflow sight glass is set at the maximum normal operating level of the tank. * **During normal operation,** the main lube oil pump must supply oil not only to the bearings but also *in excess* of the system's consumption rate to continuously refill the gravity tank. * **Oil flowing through the overflow sight glass** means the tank is full, and the oil being pumped into the tank exceeds the capacity of the tank itself (or the demand of the system), causing the excess oil to spill back to the main oil reservoir (sump) via the overflow line. * **This continuous overflow** confirms that the main lube oil pump is functioning correctly and is supplying a sufficient, and likely ample, flow of oil to maintain the required level in the gravity tank for emergency use. **Why the other options are incorrect:** * **A) Turbine bearing failure has occurred:** While bearing failure can cause oil temperature changes or contaminants, it does not directly cause the gravity tank to overflow. The gravity tank overflow is an indication of pump delivery capacity, not bearing health. * **B) Excessive oil is stored in the gravity tank:** This statement is technically redundant but misleading. The tank is designed to be full during normal operation. The act of flowing through the *overflow* sight glass simply confirms that the supply flow rate is sufficient to maintain the full level, which is the expected and desired operational state. "Excessive oil" in this context usually refers to an overfilling situation where the tank is being supplied correctly. * **C) Insufficient oil is being pumped to the gravity tank:** If insufficient oil were being pumped, the level in the gravity tank would drop below the overflow level, and no oil would be observed flowing through the overflow sight glass.