B4 Mica Shield

The B4 Mica Shield is an essential element used in a Transparent Level Gauge used in order to protect the sight glasses from corrosion from the boiler steam water.

Refraction principle with mica shields
From the rear, incident light passes through both mica shields with the medium between them. The medium is arranged at an angle. In the gaseous phase, the light passes directly through, with liquid, the light is refracted sideways. Thus the level is visible as a black column, the gaseous area as a light column over it.