Question 37 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B **Explanation for Option B (Correct Answer):** The normal operating water level (NOWL) for a boiler equipped with tri-cocks (test cocks) is conventionally established at the point where the middle tri-cock is located. Boiler safety standards and design principles dictate that these three cocks mark critical points: * The uppermost cock (A) generally indicates the maximum safe water level. * The **middle cock (B)** indicates the standard, safe, or normal operating water level (NOWL). Maintaining the water level at this point ensures maximum efficiency and safe steam generation. * The lowermost cock (C) indicates the minimum safe water level, below which the furnace crown or heating surfaces are exposed to overheating damage. Therefore, when using the tri-cocks to determine the water level, the level should register at the middle cock for normal operation. **Explanation of Incorrect Options:** * **A) At a point coinciding with the uppermost tri-cock:** This level represents the maximum safe water level. Operating consistently at this level increases the risk of priming (water being carried over into the steam line), which can damage turbines or engines. It is not the *normal* operating level. * **C) At a point coinciding with the lowermost tri-cock:** This level represents the absolute minimum safe water level. Operating at or below this point is dangerous, as it exposes the crown sheet or heating tubes to direct flame/hot gases, leading to overheating, failure, and potential explosion. This is a critical low limit, not the normal operating level. * **D) The level can normally be anywhere within the water column:** While the water level *fluctuates* during operation (due to load changes, feed pump cycling, and rolling/pitching of the vessel), the target or *normal operating* water level (NOWL) is a specific design point, which is marked by the middle tri-cock. Allowing the level to fluctuate widely or arbitrarily throughout the entire column is poor practice and potentially unsafe.