What must the water gage glass be fitted with when the boiler operating pressure exceeds 100 psi?

When the boiler operating pressure exceeds 100 psi, it is essential to have a water gauge glass fitted with a gate-type or plug-type valved drain. This requirement is in place to ensure safety and allow for proper maintenance and operation oversight. The valve enables operators to safely drain water from the gauge glass, which is crucial for accurate readings and prevents the risk of steam or hot water escaping from the gauge, potentially leading to hazardous situations.

The use of a gate-type or plug-type valve enhances the ability to isolate the water column in the gauge glass, ensuring that if maintenance is required, it can be performed without allowing pressurized water or steam to escape. This feature is especially important in high-pressure systems, where the dangers associated with pressurized steam or water are significantly elevated.

While the other options listed could serve important roles in boiler operations, they do not directly pertain to the specific safety measure required for gauge glasses at pressures exceeding 100 psi.