Question 50 QMED03 - Oiler

The Correct Answer is C ### Why Option C (Ahead throttle will close.) is correct: The lubrication system is critical for the safe operation of any rotating machinery, especially high-speed steam turbines and reduction gears. If both the main and standby lube oil (LO) pumps fail, the pressure in the LO supply header drops rapidly (typically to zero). Turbines, particularly large marine propulsion units, are equipped with sophisticated safety systems designed to prevent catastrophic failure (a "trip"). The most immediate and crucial safety action taken upon sensing a loss of lube oil pressure is the activation of the **Overspeed Trip Mechanism (or Emergency Trip System)**, which simultaneously closes the steam inlet valves (the main ahead throttle and the sentinel/guardian valves). This action immediately removes the driving power to the turbine, preventing the bearings and gears from seizing, melting, or destroying themselves due to friction and overheating caused by the lack of lubrication. Therefore, the closure of the ahead throttle is the **first operational change** triggered by the safety system in response to the pump failure. ### Why the other options are incorrect: **A) Lube oil sump will overflow.** This is incorrect. The sump holds the bulk of the oil. Pump failure stops the transfer of oil from the sump to the system. While some oil will drain back from the piping and coolers to the sump, this process is gradual and will not cause an immediate overflow. Furthermore, safety systems react to pressure loss, not sump level changes, and the safety trip occurs long before any level issue becomes critical. **B) Vacuum will be lost.** This is incorrect. Vacuum is maintained by the condenser and air ejectors, which are separate systems. While the eventual complete seizure of the turbine rotor could lead to a systemic shutdown affecting auxiliary systems, the immediate, targeted safety response to LO pressure loss is the closing of the steam inlet, which occurs almost instantaneously upon sensing the low pressure, and precedes any loss of vacuum. **D) Shaft brake will engage.** This is incorrect. The shaft brake is typically used only at low speeds or when the shaft is stopped to prevent rotation during maintenance, or sometimes to stop rotation after a major emergency trip. Engaging the shaft brake at full sea speed while the propulsion train is still spinning freely (even without steam) would cause extreme friction, wear, and possibly catastrophic damage to the brake assembly and shaft. The safety trip (closing the throttle) occurs first to remove power; the shaft brake, if fitted, would only be applied after the turbine has slowed down significantly or stopped.