Type 391 - PN16-40 with welding adapter | ACI Industriearmaturen GmbH

Circular Sight Glass Fittings Type 391 - PN16 - with weld adapter for pipeline

SHORT DESCRIPTION - CIRCULAR SIGHT GLASS Type 391 with welding adapter for pipelines

The ACI tank sight glass Type 391 is a round tank sight glass intended for welded installation on an existing pipe or small pressure vessels.

The sight glass window is made from our high quality Maxos® borosilicate glass according to DIN 7080, which has proven its reliability in most of our tank sight glasses. Alternatively, for elevated temperatures, we use high performance glass materials like quartz or sapphire glass.

For sealing we apply the same high quality flat gasket materials we use in most of our sight glass devices. We can offer universally applicable aramid fibre gaskets C4400 of the KlingerSIL brand as well Frenzelit novaphit MST. In addition to the full product range of these manufacturers we also offer special materials like Garlock Gylon or elastic materials like NBR, EPDM or silicone.

The specially adapted connection allows the sight glass Type 391 to provide a comparatively large window diameter. To ensure full compatibility with your existing piping and process, we offer Type 391 in a wide range of steel and stainless steel alloys like 1.4571, 1.4404, P265GH, as well as special alloys like Hastelloy or Duplex steel.

Contact our team to find the perfect solution for your application!

Technical details


all common materials


Sight glass with welding end, adapted to tank or pipeline rounding

Nominal size:


Nominal pressure:

depending on version


With soda lime glass up to max. 150 ° C

With borosilicate glass up to max. 280 ° C

With borosilicate & mica shield up to 320 ° C


Optional versions are possible.

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Type 391 - PN16-40 with welding adapter