Question 65 AEL01 - Assistant Engineer - Limited

The Correct Answer is C ### Why Option C is Correct Option C describes the standard, safe, and effective procedure for blowing down a boiler gauge glass (or water level gauge) to ensure the accuracy of the reading. The goal of the blowdown is to clear any sludge, scale, or debris that might be blocking the passages connecting the gauge glass to the boiler drum, thereby causing a false water level. The procedure involves blowing down the connections individually: 1. **Close the Gauge Glass Drain Valve.** (This is the starting position, assuming the blowdown is about to begin.) 2. **Close the Lower (Water) Cut-Out Valve and the Upper (Steam) Cut-Out Valve.** 3. **Open the Drain Valve.** (This depressurizes the glass.) **The Blowdown Sequence (as described in C):** 1. **First Blow (Clearing the Water Column/Lower Connection):** Close the Upper (Steam) Valve and open the Lower (Water) Cut-Out Valve. This forces boiler pressure through the lower connection, effectively clearing any blockage or sediment from the lower water leg and its connection to the boiler drum. 2. **Second Blow (Clearing the Steam Column/Upper Connection):** Close the Lower (Water) Cut-Out Valve and open the Upper (Steam) Cut-Out Valve. This forces boiler pressure through the upper connection, clearing any blockage or condensate from the steam leg. 3. **Return to Service:** Close the Drain Valve. Open the Upper (Steam) Cut-Out Valve fully, followed by the Lower (Water) Cut-Out Valve fully. The water level should return quickly and settle at the correct operating level. This two-step process (lower connection first, then upper connection) ensures that both passages are independently cleared of obstruction, verifying the integrity of the entire system. ### Why Other Options Are Incorrect **A) The gauge glass should be blown down once with the lower cut-out valve open.** This procedure only attempts to clear the lower (water) connection. It does not verify that the upper (steam) connection is clear. If the upper connection is plugged (e.g., with scale or trapped condensate), the gauge will register a false, high water level even after this blowdown. **B) The gauge glass should be blown down once with both the upper cut-out and lower cut-out valves open simultaneously.** While this setup effectively blows down the gauge glass itself, it does not provide the high-velocity flow needed to independently scour and verify the integrity of the connecting piping (the lower water leg and the upper steam leg). It is less effective than the individual blowdown procedure for clearing blocked lines leading to the boiler drum. **D) 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.** This is technically the inverse of the correct procedure (C). While blowing the connections individually is key, it is standard practice to blow the water connection first (to remove sediment which tends to accumulate there) and then the steam connection. Reversing the order does not change the effectiveness drastically, but the established industry best practice (Option C) prioritizes clearing the lower, sediment-prone connection first. More importantly, this option is simply not the prescribed method found in standard boiler operational manuals.