Question 69 MODE01 - Chief MODU Engineer

The Correct Answer is C ### Explanation for Option C (Correct) The speeder spring (also known as the speed setting spring) in a conventional mechanical governor (like a hydraulic governor used on a main propulsion diesel engine) acts to oppose the centrifugal force generated by the flyweights. The tension of this spring sets the desired engine speed (RPM). When the engine is operating at full load and the speeder spring breaks: 1. **Loss of Opposing Force:** The flyweights, which are driven by the engine, lose the force that was balancing them (the speeder spring tension). 2. **Flyweights Move Out:** Since the flyweights are still rotating at high speed and are no longer constrained by the broken spring, they will move outward (due to centrifugal force) to a greater extent than before. 3. **Fuel Rack Movement:** The outward movement of the flyweights acts through the linkage to move the pilot valve and/or the power piston, which ultimately reduces the fuel delivered to the engine (closing the fuel rack). 4. **RPM Decrease:** Because the fuel delivery is reduced while the engine is still at full load (requiring maximum fuel), the engine will slow down. 5. **New Equilibrium:** The engine RPM will decrease until the centrifugal force of the flyweights (which is proportional to RPM²) is once again balanced by the only remaining forces (the minimum tension of the broken spring fragments or the minimal spring force from the flyweight mechanism itself) and the forces transmitted by the linkage. This new, slightly lower speed will represent the new point of equilibrium for the now-weakened governor system. Therefore, the engine RPM will **decrease to a slightly lower value**. ### Explanation for Incorrect Options **A) remain the same until manually changed:** This is incorrect. The governor's function is to maintain speed against changes in load by manipulating fuel. A catastrophic failure of a primary control element (the speeder spring) immediately unbalances the system, causing the governor to reduce fuel delivery and thus forcing a change in RPM. **B) increase until the overspeed trip is actuated:** This is incorrect. The speeder spring determines the *set point* for the governor. If the spring breaks, the force demanding high RPM is lost, allowing the flyweights to move outward and immediately reduce fuel. An increase in speed occurs if the load drops or if the flyweights are somehow prevented from reacting to the existing speed (e.g., stuck linkage), but not due to the loss of the speeder spring itself. **D) hunt until stabilized by the droop rod:** This is incorrect. Hunting (unstable oscillation) occurs due to poor governor adjustment (e.g., low droop setting, issues with the compensating needle valve, or high friction). While the broken spring creates instability, the initial, immediate effect is a definite speed drop as the governor reduces fuel flow. Furthermore, the droop mechanism (which provides stable speed regulation based on load) cannot counteract a physical failure like a broken speeder spring; it can only help stabilize the engine at its new, lower speed equilibrium point.