Question 15 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is C ### 2. Explanation of Why Option C is Correct Option C states: "The selector handle is placed in either position the '1' or '2' position regardless of the load or rpm on the engine. The selector handle is temporarily placed in the 'BOTH' position only when transitioning from a restricted filter element over to a clean filter element." This statement accurately describes the standard operating procedure for a duplex (changeover) fuel filter system: 1. **Single Element Operation:** Duplex filter systems are designed so that a single filter element (either 1 or 2) has sufficient flow capacity to handle the maximum fuel requirements of the engine, even under full load (high RPM/high load). Therefore, the engine is always run using only one element at a time (Position 1 or Position 2). 2. **Purpose of Duplex System:** The primary purpose of having two filters is to allow for **continuous operation** while maintenance is performed. If the engine is running on Filter 1 and the restriction indicator shows it is clogged, the operator switches to Filter 2. 3. **The "BOTH" Position:** When switching from the fouled element (e.g., 1) to the clean element (e.g., 2), the selector handle must pass momentarily through the "BOTH" position. This momentary alignment ensures that the fuel flow to the high-pressure injection pump is never completely cut off. Interrupting the fuel flow, even briefly, could cause the engine to stall or, more commonly, lead to severe cavitation damage to the fuel pump. The "BOTH" position is solely for transition, not for continuous running. ### 3. Explanation of Why Other Options Are Incorrect **A) The selector handle is normally placed in the "BOTH" position regardless of the load or rpm on the engine...** * **Incorrect.** Running continuously in the "BOTH" position defeats the primary purpose of the duplex system, which is to allow one element to be serviced while the engine remains operational on the other. If both are in use, neither can be safely removed or replaced while the engine is running. Furthermore, the capacity of a single filter element is already sufficient for maximum throughput. **B) The selector handle is placed in the "BOTH" position when the engine is running at low load or rpm. When the engine is running at high load or rpm, the selector handle is placed in either the "1" or "2" position depending upon which filter element is clean.** * **Incorrect.** Load/RPM is generally irrelevant to whether one uses a single filter or both. Single-filter operation (1 or 2) is the standard at all times. Using "BOTH" at low load provides no benefit and complicates maintenance unnecessarily. **D) The selector handle is placed in the "BOTH" position when the engine is running at high load or rpm to accommodate higher fuel delivery requirements. When the engine is running at low load or rpm, the selector handle is placed in either the "1" or "2" position.** * **Incorrect.** This is a common operational misunderstanding. As stated above, a single element is sized to handle maximum fuel flow requirements (high load/RPM). Running in "BOTH" at high load is not necessary for flow accommodation and is poor operating practice regarding filter maintenance and safety. Continuous operation must be maintained on a single element (1 or 2).