“Armored” Gage Glass design with flat glass insert, sometimes known as “gage glass column”

Reflex glass is also known as prismatic, or “reflective”, or “single sided”, or “U-bolt type”
Glass is retained in cast steel cover flange, deeply recessed and surrounding glass on the sides, “wrap-around” style. Chamber is machined in single piece, from square bar. Sealing gasket sits on flat top of gage chamber, and is retained along its thickness by the recessed area of the cover flange. Glass seating surface of the chamber is flat without recess, making it easy to maintain with a flat file during maintenance. A recessed seating area in the chamber is not required for seal gasket retention under high fluid pressures

The 45 degree prisms on the inner face of the glass create an optical effect in the liquid zone, appearing dark or sometimes black to the observer. The vapor or gas zone shows silvery like a mirror, because of light reflection off the prisms

Reflex gages are lighter weight than transparent type because they have only one glass and cover flange per segment (section), and therefore less expensive. Reflex type gages are normally the first choice for two phase systems where there is one liquid phase and one gas phase. Reflex glass is suitable for low pressure steam service, the water showing dark and the steam showing silvery. Other applications are water & air, water & natural gas, hydrocarbon liquid & natural gas, ammonia liquid & ammonia vapor, chemical liquid & various vapors