Question 63 OSE02 - Assistant Engineer - OSV

The Correct Answer is C. **Explanation of why option C is correct:** The water column on a steam boiler provides a visual indication of the water level inside the drum. It typically features three primary test cocks, known as tricocks: the highest (steam space), the middle (normal operating water level, or NOWL), and the lowest (low water level). 1. **Uppermost Tricock:** This tricock is positioned well above the NOWL, in the steam space of the boiler drum. When opened, it should always discharge **steam**. 2. **Lowermost Tricock:** This tricock is positioned at the lowest safe operating water level (or the low water warning level), meaning it is always submerged when the boiler is operating correctly. When opened, it should always discharge **water**. 3. **Middle Tricock (NOWL):** This tricock is positioned exactly at the Normal Operating Water Level (NOWL). Because of boiler instability (swelling, surging, and turbulence) and the nature of the water-steam interface, the water level within the gauge glass and the column itself is constantly fluctuating around the NOWL. When the middle tricock is opened, it may discharge saturated **steam** (if the water level momentarily drops below the cock's orifice) or **water** (if the level is momentarily above it). Therefore, the discharge from the middle tricock is indeterminate, issuing *either* steam or water/a mixture. Since the boiler is operating at the NOWL, the results are: Steam (High), Water/Steam (Middle), Water (Low). This matches option C. **Explanation of why the other options are incorrect:** * **A) Steam should issue from the uppermost tricock, and water should issue from both the middle and lowermost tricocks.** This is incorrect because, at the NOWL, the middle tricock is at the water-steam interface and will not consistently discharge only water. It may discharge steam or a mixture. * **B) Steam should issue from both the uppermost and middle tricocks, and water should issue from the lowermost tricock.** This is incorrect because the boiler is operating at NOWL. While the middle tricock *might* discharge steam, it is not guaranteed. If the water level is stable or slightly high (still within NOWL tolerance), it will discharge water. It is not designed to be consistently in the steam space like the uppermost tricock. * **D) Water should issue from each of the uppermost, middle, and lowermost tricocks.** This is incorrect. The uppermost tricock is situated in the steam space and must issue steam when the boiler is operating correctly, confirming that the water level is not dangerously high. Issuing water from all three would indicate an excessively high water level (a flooding condition).