Figure 1 (a) shows a gauge glass which is used for vessels where the liquid is at ambient
temperature and pressure conditions. Figure 1 (b) shows a gauge glass which is used for vessels
where the liquid is at an elevated pressure or a partial vacuum. Notice that the gauge glasses in
Figure 1 effectively form a "U" tube manometer where the liquid seeks its own level due to the
pressure of the liquid in the vessel.
Gauge glasses made from tubular glass or plastic are used for service up to 450 psig and 400°F.
If it is desired to measure the level of a vessel at higher temperatures and pressures, a different
type of gauge glass is used. The type of gauge glass utilized in this instance has a body made
of metal with a heavy glass or quartz section for visual observation of the liquid level. The glass
section is usually flat to provide strength and safety. Figure 2 illustrates a typical transparent
Figure 2 Gauge Glass