Sight Glass

Sight glass is used in industrial plants and machines in order to visually observe and monitor liquid and material levels, colors, flows or direction. It can be installed as the windows of a piping system, an external vacuum tube, or as a component with a frame screwed between two metal pipes.

Tanks, boilers, reactors or vessels may contain components of sight glass in the form of liquid level gauges or inline sight points. Further uses include media vessels in chemical plants and in other industrial settings such as breweries, bio gas plants, pharmaceutical, food processing and beverage.

Also referred to as sight windows or sight ports, sight glass components are important for a number of reasons. For consumer and beverage industries it is necessary to ensure levels remain high. In some machines, without a specific amount of necessary liquids, the engines could seize and cause great damage; therefore it is imperative the levels are monitored to remain in a safe phase.

Sight glass can come in different forms; however the most common type of sight glass is composed of a tempered glass disc between two metal frames which have been secured together allowing the operator of the equipment to determine the level of liquid contained within.

The glass used must be transparent in order for the level of liquid to be observed and therefore color additives or coatings are not typically used with sight glass. However, to ease the reading of the level, a backboard may be a component of the sight glass mechanism.

Sight glass is typically manufactured as safety glass in order to prevent any pressure or tension resulting in breakage and potential physical damage to personnel working with the machinery. However, glass which has been tempered or mechanically stressed prior to installation is less likely to break and therefore it is used for sight glass to reduce the risk of explosions. The glass used for sight glass fabrication is made using soda lime or borosilicate glass.

Soda lime glass tends to be more cost-effective and is a good quality material. However, when tensile strength and a lower coefficient of expansion are required in a piece of sight glass, more expensive borosilicate glass is used. It is unlikely that borosilicate glass will crack or break even when exposed to temperature changes and pressure. Sight glass can be further strengthened through the process of annealing and ion exchange chemical strengthening.

Sight Glass Informational Video