What does a gauge glass show in a boiler?

• A. A pressure gauge displays pressure; a gauge glass shows water level.
• B. A gauge glass displays pressure.
• C. A pressure gauge shows water level.
• D. A gauge glass measures flow rate.

Answer: (A)

Gauge glass serves as a visual water-level indicator in a boiler. It lets the operator see whether the water is at the proper level inside the boiler’s water-containing space. The height of the liquid in the glass reflects the actual water level, and the glass is fed through gauge cocks and tubes to the boiler for this reading. It does not measure pressure or flow rate—that’s what a separate pressure gauge does. Maintaining the correct water level is essential to prevent overheating of exposed tubes or steam-water carryover.