Question 57 MODE01 - Chief MODU Engineer

The Correct Answer is C ### Explanation for Option C (Correct Answer) The problem states that the desired tripping speed is 900 RPM + 10\% overspeed, which is $900 \times 1.10 = 990$ RPM. However, the governor is currently activating (tripping) at 930 RPM. This means the engine is tripping too early (at a lower speed than intended). The overspeed trip mechanism operates by balancing the centrifugal force generated by the throw-out weight (piece #10) against the opposing force exerted by the spring (piece #12). * **To trip later (at a higher RPM),** the centrifugal force required to overcome the spring must be greater. * **To increase the opposing force of the spring,** the compression on spring #12 must be increased. Increasing the spring compression requires the throw-out weight to spin faster (generate more centrifugal force) before it overcomes the spring tension and activates the trip mechanism. Therefore, increasing compression on spring #12 will raise the tripping speed from 930 RPM towards the desired 990 RPM. ### Explanation for Incorrect Options **A) decrease compression on spring #12:** Decreasing the spring compression would make it easier for the throw-out weight to move outward. This would lower the tripping speed even further below 930 RPM, worsening the current problem. **B) install a larger throw out weight piece #10:** A larger (heavier) throw-out weight generates more centrifugal force at any given speed ($F_c \propto m$). Installing a larger weight would cause the trip to activate at an even lower RPM than 930 RPM, worsening the problem. (Alternatively, if the desired speed was maintained, a lighter weight would be needed, not a larger one.) **D) change the angle of the operating face by machining piece #10:** Machining the angle of the operating face changes the mechanical leverage or the geometry of how the weight acts against the trip linkage. While this is a design parameter, changing the angle is usually a drastic measure related to the overall sensitivity curve or stroke length, not the primary adjustment for correcting a simple overspeed set point error. The standard and correct method for adjusting the trip speed set point is always to adjust the spring tension (compression).