Minnesota Boiler License Practice Exam

In the HRT boiler, the fuse plug is located in the rear head, how many inches above the top row of tubes?

1. 2 inches

2. 1/2 inch

3. 1 inch

4. 3 inches

The correct answer is: 2 inches

In a horizontal return tubular (HRT) boiler, the fuse plug serves a vital safety function. It is designed to melt and operate when the water level in the boiler drops below a certain point, thereby preventing the boiler from overheating and potentially causing an explosion. The correct placement of the fuse plug is crucial for effective operation. For HRT boilers, the standard specification places the fuse plug typically 2 inches above the top row of tubes. This distance is intentional, ensuring that the water remains sufficiently high to cover the tubes during normal operation, while also providing an immediate safety response if the water level falls. By being positioned at this height, the fuse plug can effectively protect against low-water conditions that could lead to tube failure and other dangerous situations. Other options, such as 1/2 inch, 1 inch, or 3 inches, do not meet the specifications and safety margins defined for typical HRT boiler designs. At 1/2 inch or 1 inch, the fuse plug would be too close to the tubes, potentially leading to inadequate thermal protection. If it were placed at 3 inches, it would be too far above the tubes, delaying the response in a low-water condition and increasing the risk of damage. Thus,