What are Tank sight glasses?

These sight glass fittings can be installed by plant engineers as needed on pipelines and containers.

Tank sight glasses are described in the standards DIN 28120 and 28121, and further variants based on the basic shapes described in the standards are now established in the market.

ACI Type 320 according to DIN 28120 includes sight glass fittings that are welded into container walls. The glass plate is inserted with the gasket on the media side into a recess of the base flange and is secured on the outside by the counter flange with a defined surface pressure. This allows for the exchange of possibly damaged glasses with relatively little effort. The procedure for this is explained in detail in the video linked in the button above.

In aggressive process media or at high temperatures above 280°C, it is possible for circular tank sight glasses according to or similar to DIN 28120 to protect the borosilicate glass plate with a mica protection screen against chemical influences and to increase the possible working temperature up to 320°C.

Sight glass fittings of the Type 321 according to DIN 28121 are designed to be mounted on a flange.

The sealing here, unlike with the Type 320, is achieved through a PTFE-coated soft material gasket in the force shunt. The flanges are screwed together with pre-tension bolts until the metal surfaces make complete contact. This defines the soft material gasket compression and ensures a reliable sealing of the sight glass fitting. This creates an almost completely closed fitting for the glass.