Question 26 QMED03 - Oiler

The Correct Answer is C. ### Why Option C (turbine-driven feed pump) is correct: An **excess pressure governor** (often simply called a feed pump governor or differential pressure regulator) is specifically designed to maintain a stable pressure differential between the discharge pressure of the boiler feed pump and the pressure within the boiler (steam drum pressure or superheater pressure). Boiler feed pumps, particularly the high-capacity, high-pressure, **turbine-driven feed pumps** found in steam plants, must always discharge water at a pressure significantly higher than the boiler pressure to overcome flow resistance (piping, valves, regulators) and ensure adequate water flow into the boiler. The governor monitors the pump discharge pressure and the boiler steam pressure. If the pump output pressure gets too high (creating excessive differential pressure), the governor automatically reduces the speed of the drive turbine (by throttling the steam supply to the turbine), thereby reducing the pump's discharge pressure until the desired differential pressure is restored. This prevents cavitation, reduces wear on valves (like the feedwater regulating valve), and ensures stable boiler water level control. ### Why the other options are incorrect: **A) forced draft fan:** Forced draft fans control the air supply to the furnace. They use automatic combustion control (ACC) systems and associated dampers or speed controls, typically based on furnace pressure or steam flow demands, not an excess pressure differential governor in the sense used for boiler feed pumps. **B) main circulator pump:** Main circulator pumps (or circulating water pumps) move cooling water (often seawater or fresh water) through condensers or other heat exchangers. Their control systems manage flow rates based on temperature and vacuum needs, typically using variable speed drives or throttling valves, not a specialized excess pressure governor designed for boiler feed water differential control. **D) low-pressure propulsion turbine:** A low-pressure propulsion turbine is part of the main engine unit that converts steam energy into mechanical shaft power for ship movement. It is regulated by the main throttle or maneuvering valves, and its controls are focused on speed and power output, not managing a differential fluid pressure required for boiler feed regulation.