To what height must low water fuel cutoff devices be piped in relation to the gauge glass?

The requirement for low water fuel cutoff devices to be piped at the lowest visible part of the water gauge glass is crucial for ensuring safe operation of a boiler system. This positioning is necessary because the low water cutoff serves as a safety mechanism to prevent the boiler from operating with insufficient water, which could lead to overheating and potential damage or catastrophic failure.

By placing the cutoff device at the lowest visible level of the gauge glass, it can accurately detect the water level and ensure that it activates before the water drops below a safe threshold. This way, if the water level gets too low and is no longer visible in the gauge, the cutoff will trigger and shut down the fuel supply to the boiler, preventing further heating without sufficient water.

The other options suggest levels that do not provide an accurate safety measure. For example, being above the highest reading or at mid-height would not reflect the true low-water conditions accurately, potentially leading to unsafe operation of the boiler. Therefore, positioning at the lowest visible part ensures a dependable measure of the actual water level and enhances overall safety in steam generation systems.