Question 12 QMED03 - Oiler

The Correct Answer is C. **Explanation for Option C (Correct):** Main propulsion turbine reduction gears operate under extremely high loads and speeds. Effective cooling and lubrication are critical to prevent overheating and wear. The most efficient and standard method for lubricating these large, high-speed gears is **spray lubrication**. Oil is pumped from a sump, filtered, cooled, and then delivered under pressure to specialized **spray nozzles** strategically aimed at the precise point where the gear teeth are coming into (the "point of mesh") and leaving engagement. This ensures a constant, directed film of lubricant is applied exactly where the maximum friction and load occur, simultaneously providing maximum cooling. **Explanation of Incorrect Options:** **A) Oil is pressure fed through internal drilled passages which force oil to the gear's periphery:** This method (internal passages forcing oil to the periphery) is primarily used for lubricating internal bearings or extremely large, slow-moving rotating machinery where the internal structure is hollow. It is not the standard or effective method for lubricating the contact surfaces of high-speed external reduction gear teeth. **B) Oil rings in channels outside the gears dip into oil in the sump and carry it to the gear teeth:** This method, known as ring oiling, is typically used for lubricating lower-speed journal bearings or shafts. It cannot supply the large volume of cooled oil under pressure necessary to lubricate and cool massive, high-speed turbine reduction gears effectively. **D) The gears run through an open oil sump and oil is carried along on the gear teeth:** This method is called splash or bath lubrication. While simple and effective for small, low-speed gearboxes (like differential gears in automobiles or small pumps), it creates excessive churning, aeration, and heat generation when used with large, high-speed gears. This excessive heat and drag would severely reduce the efficiency and lifespan of large propulsion reduction gears.