Question 46 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is A. **Explanation of why option A is correct:** 1. **Context:** The question describes a boiler water column (gauge glass) operating at the Normal Operating Water Level (NOWL). Tri-cocks (or gauge cocks) are installed at specific vertical positions relative to the NOWL to confirm the water level independently of the glass gauge. 2. **Uppermost Tri-cock:** The uppermost tri-cock is typically located well above the NOWL and the highest visible water level in the gauge glass. Since the boiler drum space above the water level is filled with steam, opening the uppermost tri-cock will release **steam**. 3. **Lowermost Tri-cock:** The lowermost tri-cock is typically located well below the NOWL and the lowest safe permissible water level. Since the boiler space below the water line is filled with water, opening the lowermost tri-cock will release **water**. 4. **Middle Tri-cock (NOWL position):** The middle tri-cock is usually placed at or very near the NOWL, often marking the level where water should usually be maintained. If the water level is exactly at the NOWL, the middle tri-cock could be just slightly above the water (releasing steam) or just slightly below the water (releasing water). Given the slight fluctuations and the design placement intended to confirm the *location* of the water line, opening the middle tri-cock will reliably release **either steam or water**, depending on the exact position of the NOWL relative to the tri-cock opening. Therefore, Option A correctly describes the expected discharge from each location: Steam (top), Water (bottom), and Either Steam or Water (middle). **Explanation of why the other options are incorrect:** * **B) Water should issue from each of the uppermost, middle, and lowermost tri-cocks.** This is incorrect because the uppermost tri-cock is positioned in the steam space above the water line, and therefore must issue steam, not water. * **C) Steam should issue from the uppermost tri-cock, and water should issue from both the middle and lowermost tri-cocks.** This is incorrect because, while the lowermost tri-cock always issues water and the uppermost issues steam, the middle tri-cock is positioned near the NOWL and is specifically designed such that it could issue either steam or water, depending on the exact level and cock placement. Stating that it *must* issue water (as implied by "water should issue from... both the middle and lowermost") is an oversimplification that ignores its function as the boundary check. * **D) Steam should issue from both the uppermost and middle tri-cocks, and water should issue from the lowermost tri-cock.** This is incorrect for the same reason C is incorrect regarding the middle tri-cock. While the lowermost issues water and the uppermost issues steam, the middle tri-cock's intended function is to confirm the boundary, meaning it could issue either substance. Assuming it *must* issue steam limits its function and ignores its placement at the NOWL.