Question 67 MODE01 - Chief MODU Engineer

The Correct Answer is D ### Explanation for Option D (Correct Answer) The compensating needle valve (or speed droop adjustment valve) in a hydraulic governor controls the rate at which the compensating oil (or pressure relief) acts on the compensating piston (buffer piston). This system is crucial for achieving temporary speed droop, which prevents hunting (oscillation) by momentarily biasing the pilot valve to overshoot the target gate position. If the compensating needle valve is opened **more than necessary** (i.e., too wide), it allows the compensating oil to equalize pressure across the compensating piston too **quickly**. 1. **Loss of Compensation:** A rapid equalization means the temporary speed droop effect (the mechanism designed to dampen oscillations) is ineffective or too short-lived. 2. **Overshoot:** The governor will effectively act like one without proper compensation—it will overcorrect the gate/rack position in response to a load change. 3. **Excessive Response:** This lack of necessary damping results in the governor producing a large, rapid, and excessive change in engine speed (overshoot or undershoot) immediately following a load change, leading to instability or oscillation (hunting). Therefore, opening the needle valve too wide produces excessive speed response to a load change. ### Explanation for Incorrect Options **A) respond slowly to any change in engine load:** * **Incorrect.** A slow response is usually caused by excessive friction, sticky linkages, or if the compensating needle valve were closed too much (creating high damping/slow return to equilibrium). Opening the valve excessively makes the governor react **too fast** and overshoot, not too slowly. **B) stabilize engine speed at the new governor setting:** * **Incorrect.** Excessive opening of the needle valve causes instability and oscillations (hunting). Stabilization is the desired function of the governor, and opening the valve too much directly compromises the ability to stabilize the speed effectively. **C) have a larger than normal deadband:** * **Incorrect.** Deadband refers to the range of speed change required before the governor starts to act (often caused by friction). The setting of the compensating needle valve primarily affects the governor's *dynamic stability* (how it reacts after it has started moving), not the size of the deadband. Excessive opening causes severe hunting, not a larger deadband.