321A Sight glasses similar to DIN 28121 | ACI Industriearmaturen GmbH

Circular sight glass fitting Type 321A 

similar to DIN 28121 for flange mounting on ASME / ANSI flanges

Tank Sight Glass Type 321A

Our round tank sight glasses type 321A are screwed onto flanges according to ASME B16.5 to allow observation or illumination of the tank interior. ACI tank sight glasses type 321A are designed in similar to DIN 28121 for operating pressures up to 20 bar. A sight glass made of chemically highly resistant borosilicate glass DIN 7080 is clamped between two high-quality stainless steel flanges and a PTFE enclosed resilient gasket on the media side. Since this gasket is in the force shunt, the flange parts of the sight glass lie directly on top of each other and thus protect the glass plate in the best possible way.


The type 321A is delivered pre-assembled from the factory and can be screwed directly onto a flange according to ASME B16.5 without any additional effort. In the unlikely event that the glass is damaged during operation, the entire fitting can be replaced with little effort.

Our tank sight glasses of type 321A are made of the high-quality stainless steel 1.4571 (316Ti), which our customers have appreciated for years. The glass material used is borosilicate glass 3.3 according to DIN 7080, which has proven itself in the industry. The sealing in the force shunt preempts setting of the gaskets, so that retightening of the clamping screws on site is no longer necessary. The PTFE-encased gasket makes the tank sight glass Type 321A suitable for foodstuffs, acids, alkalis and the most aggressive chemicals.

Should the process conditions pose a problem even for the highly resistant borosilicate glass, an FEP or mica protective screen specially adapted for the fitting offers additional protection against steam and aggressive chemicals, such as alkalis up to a pH value of 14.

As with other of our sightglass fittings, our Type 321A can be optionally fitted with sprayers, SWI type wipers or lights.

More technical details about our tank sight glass type 321A following DIN 28121 can be found further down this page!

Technical data

Flange material:

  • Base flange: 1.4571 (factory standard)
  • Cover flange: 1.4571 (factory standard)
  • 1.4301/7, 1.4404, 14539, 1.4541, 1.4435, 1.4462
  • Other materials on request


  • according to DIN 28121


  • up to 200 °C¹ with borosilicate glass according to DIN 7080

Sight glass:

Nominal size:

    2" up to 8"


  • Wiper SWI with PTFE or silicone wiper blade
  • LED lights for EX- and Non-EX-areas
  • Spray device SVII
  • FEP protective screen (for higher pH-values)
  • special desgins are possible 


  • PTFE enclosed resilient gasket

Nominal pressure:

  • Class 150


  • A4-80
¹Limited by gasket material

DN 2" 3" 4" 5" 6" 8"
Da [mm] According to DIN EN 1092-1
L [mm]
K [mm]
Di [mm] 65 80 100 125 125 150
H [mm] 41 50 59 66 66 66
kg 3,8 8 13,5 17,4 23 36,7

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321A Sight glasses similar to DIN 28121