What is a flow sight glass?
A flow sight glass is a pipeline element with a transparent window that gives a clear view of the flowing medium. The body is installed as a flanged sight glass between two pipe flanges or as a threaded sight glass screwed directly into the line. The glass sits in a stainless steel frame and is sealed with a PTFE gasket. A pipeline sight glass serves visual inspection only — it has no shut-off function. The face-to-face length of the flanged version follows EN 558-1 Series 1.
Stainless steel sight glass — GD100 technical data
- Nominal size: DN15 to DN250 (flanged), DN15 to DN50 (threaded)
- Connection: flange PN10/16 to DIN 2501, female thread ISO 7-1 (EN 10226-1) F-F
- Body: stainless steel 1.4408 (CF8M) or ductile iron GGG40.3+PFA
- Glass types: borosilicate (DIN 7080), toughened pressed glass, soda-lime tempered glass
- Gasket: PTFE
- Operating pressure: 10/16 bar
- Temperature: up to +240 °C (glass dependent)
- Face-to-face (flanged): EN 558-1 Series 1
- Conformity:EU Pressure Equipment Directive 2014/68/EU
Borosilicate, toughened pressed glass or soda-lime — which glass to choose?
| Glass type | Standard | Strength | Typical applications |
|---|---|---|---|
| Borosilicate | DIN 7080 | highest temperature & chemical resistance | steam, aggressive liquids, pharma, food |
| Toughened pressed | — | high mechanical impact resistance | industrial standard with impact risk |
| Soda-lime tempered | — | proven standard glass, economical | water, oil, heating, cooling circuits |
Choose a borosilicate sight glass for steam and aggressive media. A toughened pressed sight glass excels in mechanically demanding environments. A soda-lime sight glass is the economical standard for water and oil service.
Flanged sight glass vs. threaded sight glass
A flanged sight glass is installed between two pipe flanges to DIN 2501 PN10/16. The flanged connection suits larger sizes from DN15 to DN250 and higher pressures. Face-to-face length follows EN 558-1 Series 1.
A threaded sight glass is screwed directly into the pipeline with female thread to ISO 7-1 (EN 10226-1). The threaded connection is more compact and suits sizes DN15 to DN50 where space is limited and quick maintenance matters. Both versions use the same stainless steel 1.4408 body and PTFE gasket.
Applications — chemicals, food, pharma and water treatment
A pipeline sight glass is used wherever visual media control improves plant safety. In the chemical industry a stainless steel sight glass with borosilicate monitors reactions and aggressive liquids. In food and pharmaceutical processing the stainless steel body and PTFE gasket deliver the required hygiene. In steam systems the sight glass shows condensate flow ahead of steam traps. In water treatment and cooling systems operators spot turbidity and contamination immediately. An upstream strainer protects the sight glass from coarse particles and extends its service life.
Sight glass in stock — EU-wide delivery
Fergo stocks all 29 sight glass variants for immediate dispatch. Standard shipping via DHL reaches customers across Europe within a few working days. Each flow sight glass ships with datasheet and declaration of conformity. For aggressive media we recommend the PFA-lined sight glass. Check material compatibility with our resistance check tool.
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