various media. Light is bent, or refracted, to a greater extent in water than in steam. For the
portion of the chamber that contains steam, the light rays travel relatively straight, and the red
lens is illuminated. For the portion of the chamber that contains water, the light rays are bent,
causing the green lens to be illuminated. The portion of the gauge containing water appears
green; the portion of the gauge from that level upward appears red.
Figure 4 Refraction Gauge Glass
The ball float method is a direct reading liquid level mechanism. The most practical design for
the float is a hollow metal ball or sphere. However, there are no restrictions to the size, shape,
or material used. The design consists of a ball float attached to a rod, which in turn is connected
to a rotating shaft which indicates level on a calibrated scale (Figure 5). The operation of the
ball float is simple. The ball floats on top of the liquid in the tank. If the liquid level changes,
the float will follow and change the position of the pointer attached to the rotating shaft.