More about Sight Glasses

Click here to find Sight Glasses Manufacturers | Discuss Sight Glasses & Other Topics

Sight glasses are transparent tubes or panels placed on various vessels and lines in order to allow a visual check of the fluid level. They are regularly used in high pressure, high temperature and vacuum applications, where they provide a dependable level indicator for users. Units are rated for a maximum pressure and window diameter, and are built to fit a specific pipe or hole size. Pressure ratings are typically designated for a specific temperature, and changes in this temperature will alter the maximum capacity.

Manufacturers produce sight glass casings from a variety of materials, including aluminum, brass and steel. The transparent sight window can be made from glass or certain synthetics, such as polycarbonate or polyamide. It may be designed as either a flat, curved or domed surface; glass is typically attached to the metal casing with a metal-to-glass seal. These seals utilize a chemical or mechanical bond between glass and metal to prevent the movement of fluid and particle through the part. Reflectors allow users to easily view dark liquids, while transparent sight glasses are typically used for clear liquids. Glass used in sight glass optics include borosilicate, soda lime and quartz; the material, size and production process affect the pressure capacity of the glass.

A variety of sight glass fitting designs are also produced by manufacturers. These include weld-in, flange, raised face flange, threaded, sanitary, oblong and bull’s eye. Threaded sights are affixed to corresponding threads on the pipe or vessel. Sanitary sights use a clamp to secure them in place, and can be easily removed from the system. Flange units are attached by various fasteners, such as bolts or screws. Weld-in sights are permanent fixtures that are welded to the vessel. See-through sight glass fixtures allow viewing at an angle perpendicular to the direction of the pipe.