Question 45 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is A **Explanation of why Option A is correct:** The purpose of blowing down the gauge glass is to ensure that the connections (the steam line via the upper cut-out valve, and the water line via the lower cut-out valve) and the glass itself are clear of obstructions, sludge, or sediment, allowing the gauge to accurately reflect the true boiler water level. The proper procedure involves blowing down the steam connection and the water connection separately to verify that each pathway is clear: 1. **First blowdown (Lower cut-out valve open):** The **lower (water) cut-out valve** is opened while the **upper (steam) cut-out valve** is temporarily closed. This forces steam and water to blow through the lower connection, verifying that the water pathway and the connection leading to the boiler drum are clear of debris. 2. **Second blowdown (Upper cut-out valve open):** The **upper (steam) cut-out valve** is opened while the **lower (water) cut-out valve** is temporarily closed. This forces steam and condensate to blow through the upper connection, verifying that the steam pathway is clear. After both connections have been verified by blowing them down separately, both the upper and lower cut-out valves are fully reopened, and the blowdown valve is closed. If the water level returns rapidly and accurately reflects the expected boiler level, the gauge is considered reliable. **Explanation of why the other options are incorrect:** * **B) The gauge glass should be blown down twice; first with the upper cut-out valve open and then with the lower cut-out valve open.** * While this also involves two steps, the standard, safest, and most effective procedure for marine and auxiliary boilers dictates checking the water connection (lower) first and then the steam connection (upper). Although the result might be similar, Option A follows the established and required sequence for verifying clarity. * **C) The gauge glass should be blown down once with the lower cut-out valve open.** * This procedure only verifies the water connection (lower leg). It does not verify that the steam connection (upper leg) is clear. If the steam connection were partially blocked, the gauge would show a falsely high and inaccurate water level, leading to a dangerous operating condition. * **D) The gauge glass should be blown down once with both the upper cut-out and lower cut-out valves open simultaneously.** * When both cut-out valves are open simultaneously during a blowdown, the steam and water mixture exits the blowdown line, but this procedure does not isolate and verify the clarity of *each* connection independently. If one connection were blocked, the flowing mixture would still be seen, potentially masking the blockage and leading to an inaccurate reading once the blowdown valve is secured. Independent verification is essential.