Flow sight glasses with three viewports type 591 - PN16 up to PN400

Flow sight glass Type 591 with three viewpor

The ACI flow sight glass Type 591 with three viewports widens your possibilities to observe processes.

Apart from the usual facing viewing openings, Type 591 has a further perpendicular viewport. Due to this layout, you do not only have the possibility to observe the medium flow from three sides or to make use of a lateral incidence of light, but the third viewing opening can easily be fitted with carriers for additional sensors, probes and other equipment. This allows our Type 591 to be converted into a versatile and modular measuring device that is already being used successfully by our customers.

Type 591 can be fitted either with our proven borosilicate glass according to DIN 7080 or, in case borosilicate glass can no longer meet your requirements, even with quartz or sapphire glass. To seal the glass panel, we use flat seals from well-known suppliers adapted individually to your requirements. Apart from soft seals made of NBR, EPDM or silicone, we stock the proven universal seal KlingerSIL C4400, robust graphite materials such as Frenzelit novaphit MST or fluoropolymers such as Garlock Gylon, which are used often in the chemical industry.

For the casing material we also consider your requirements fully. Apart from proven types of steel for pressure equipment, including S235JRG2 or P265GH, we stock corrosion-resistant stainless-steel alloys such as 1.4404 and 1.4571. For the highest requirements, we can also manufacture your fitting on request out of special alloys such as Hastelloy or other high-quality materials that will meet your requirements.

Find detailed information on this page about Type 591 and make use of our detailed graphics, animation and 3D views

Technical data


Body Material:
P235GH, P265GH, 1.4404 or 1.4571

Glass plates: Borosilicate glass DIN 7080, soda lime glass DIN 8902, quartz glass; META® glass

Gasket: PTFE / FKM / NBR / C4400 / Silicone / EPDM / Graphite or as required.


straight flow sight glasses with 3 viewports

This version is particularly suitable for mounting a lighting device.

Nominal size:

DN50 up to DN100

(other dimensions on request)

Nominal pressure:

PN16 / PN40 / PN63 / PN100 / PN160 / PN250 / PN 320 / PN400


with borosilicate glass DIN7080 max. 280 ° C

with soda lime glass DIN8902 max. 150 ° C

Special solutions for higher temperatures available upon request!

Special materials, quartz glass, metal fused glasses, heating mantle, lighting device, etc.

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Sight glass type 591 -with 3 viewports