What Is Steam Boiler Gauge Glass?

Structure

• The most common and simplest kind of gauge glass is merely a transparent tube attached to the side of the boiler. The tube enters the boiler in two places: near its base and near the top. The height of the liquid in the gauge will equal the height of the water in the boiler, so an operator can determine the boiler water level merely by glancing at the gauge, which forms a sort of U-shape along the outside of the boiler.

Materials

• The materials chosen for the gauge glass depend on the amount of pressure it must sustain. Tubes of glass or plastic work for temperatures below 400 degrees Fahrenheit and pressures below 450 pounds per square inch. Under other conditions, the gauge glass must be somewhat more robust. Typical designs have a metal-body tube or conduit with a quartz or quartz glass panel so the operator can see the water level inside. The quartz glass is generally flat to provide increased strength.

Reflex Glass

• Reflex gauge glasses are another variation on the same theme. The tube body is again made of metal and fastened to the body of the boiler with strong bolts, just like other high-pressure gauge glasses. In this case, however, one part of the quartz glass is shaped like a prism. The presence or absence of liquid in the chamber behind the quartz glass determines whether light traveling through this prism-like surface is reflected back outward or refracted. Air inside the chamber causes the glass to appear silvery-white, while liquid inside the chamber causes it to appear dark.

Refraction Glass

• Another type of gauge glass is called a refraction glass. The basic idea is that water will bend or refract incoming rays of light to a greater extent than steam does. Light passes through one side of the chamber and out the other. If it is refracted to a large extent, it passes through a green lens positioned off to one side; if it is only refracted to a minimal extent, it passes through a red lens positioned on a straight line from the light. Consequently, the presence or absence of water in the chamber determines which color the operator will see.