Professional Article: Tank sight glasses
This professional article will give you an overview of tank sight glasses, their typical designs and possible applications.
Tank sight glasses are flat steel flanges that are, depending on the specific type, either welded into the wall of a pressure vessel or fixed to carrier flanges. Some common types of tank sight glasses are shown in Figure 2.
These sight glass fittings can be installed as required in processing plants of any kind.
Tank sight glasses are primarily defined in the German Industrial Standard documents DIN 28120 and DIN 28121. Additional variations have been effectively established as standards in practice based on these two documents.
ACI Typ 320 acc. DIN 28120 (Figure 2) is a type of sight glass fitting to be welded into the side of a pressure vessel. The glass plate, together with the inside gasket, is inserted into a recess on the base flange. On the outside, a cover flange is used to fix the glass plate to the base flange and apply a defined pressure to the system of base flange, gasket and glass. This allows for a comparatively easy exchange of broken or damaged glass plates. The following video explains the procedure in detail.
Video 1: Changing sight glass plates
In the presence of corrosive process media or high temperatures (above 280°C), the sight glass disc can be protected from chemical influences by an added mica layer, simultaneously increasing the allowable operating temperature to 300°C.
Sight glass fitting of Typs 321 acc. DIN 28121 (Figure 3) are intended for mounting on a flange.
The sealing method for this type is different from type 320 (Figure 2) in that it uses a PTFE enclosed resilient gasket system in off-load contact. As shown on the right side of Figure 3, this creates a nearly completely closed fitting for the glass disk. Sight glass devices according to DIN 28121 do not need to be disassembled for installation or maintenance. Replacement of the glass disk or gasket is not intended in the field, and should be performed by the manufacturer if required.
Based on the definitions of DIN 28121, ACI Industriearmaturen GmbH has designed and manufactured tank sight glasses suitable for temperatures above 500°C and pressure exceeding 100 bar.