Online Store

Industriearmaturen Sight Glass

Sight Glasses in Stainless Steel & PFA Lined

Flow sight glasses with flange or thread, stainless steel 1.4408 or PFA-lined ductile iron, borosilicate, soda-lime or pressed tempered glass, DN15 to DN250.

Buy now in the shop →

Sight Glass
  • Flow sight glass type GD200

    Flow sight glass type GD200

    Sizes: DN15 – DN250

    Flange connection: PN10-40, ANSI/ASME Class 150/300

    Case material: Edelstahl, Stahlguss, Grauguss, Sonderwerkstoffe

    Dichtung: Graphit

    Glas: Borosilikat nach DIN 7080 (bis 280°C), Natron-Kalk-Glas nach DIN 8902

  • Flow Sight Glass Type GD100

    Flow Sight Glass Type GD100

    Sizes: DN15 – DN50, 1/2" – 2"

    Flange connection: PN10, PN16

    Case material: 1.4408

    Dichtung: PTFE

    Thread: DIN 2999, ISO 7/1

Product Overview

Sight Glasses: Visual Monitoring for Pipelines and Processes

A sight glass makes the medium in a pipeline visible. A pressure-resistant glass disc sits inside the valve body and opens the view directly into the process. As a result, operators recognise flow, turbidity, colour changes, gas bubbles and contamination immediately. A flow sight glass therefore shortens fault diagnosis and protects downstream equipment.

Fergo supplies the GD100 series in stainless steel 1.4408 (CF8M) and the PFA-lined ASG series from Flowserve Atomac. Nominal sizes reach from DN15 up to DN250. Connections are available as female thread to ISO 7-1 (EN 10226-1) or as flange to DIN 2501 and EN 1092 in PN10 and PN16. A PTFE gasket handles operating temperatures up to +240 °C.

Sight glasses serve the chemical and petrochemical industry, pharmaceutical production, food and beverage plants, water treatment plants and general mechanical and process engineering. They monitor reaction processes, dosing lines, condensate streams and cleaning cycles. Installation is straightforward directly into an existing line. Fitting a Y-strainer upstream additionally keeps particles off the viewing disc and extends visibility over time.

Subcategories: Sight Glasses by Connection Type

01 Threaded Sight Glasses (GD100)

The threaded sight glasses of the GD100 series carry a female thread to ISO 7-1 (EN 10226-1) in an F-F design. Body and cover are made of stainless steel 1.4408 (CF8M), with soda-lime tempered glass as the standard viewing disc. The nominal size range covers DN15 to DN50 at 16 bar. This compact design suits tight installation situations, small dosing lines and quick maintenance access.

02 Flanged Sight Glasses (GD100)

For larger nominal sizes and higher flow rates, Fergo supplies flanged sight glasses with connection to DIN 2501 PN16. Face-to-face length follows EN 558-1 series 1. Body and cover are stainless steel 1.4408, the viewing disc is pressed tempered glass, and the gasket is PTFE. The pressure range covers 10 to 16 bar, and the temperature limit reaches +240 °C. Available from DN15 up to DN250.

03 PFA Lined Sight Glasses (ASG)

For highly corrosive media Fergo carries PFA lined sight glasses of the Flowserve Atomac ASG series. The ductile iron GGG40.3 body is fully PFA-lined, and the viewing disc is borosilicate glass to DIN 7080. Flange connection follows DIN EN 1092-2 PN16, with face-to-face length to EN 558 base series 1. This design extends the wider PFA lined valves programme with a matching visual monitoring option.

Materials in Detail: Specifying the Right Sight Glass

Body and Sealing Materials

1. Stainless Steel 1.4408 / CF8M (GD100)

  • Application: chemical and pharmaceutical processing, food and beverage plants, water treatment, mechanical engineering, steam and condensate
  • Temperature: up to +240 °C (with PTFE gasket) · 10 to 16 bar
  • Advantages: high corrosion resistance through molybdenum, hygienic smooth surface, dimensionally stable and durable
  • Limitations: not resistant to hydrofluoric acid and strongly reducing acids

2. Ductile Iron GGG40.3 with PFA Lining (ASG)

  • Application: concentrated acids and alkalis, halogen compounds, chemical processing, semiconductor fabrication
  • Temperature: −20 °C to +200 °C · up to 16 bar
  • Advantages: near-universal chemical resistance, mechanical stability of the ductile iron housing, no metal contact with the medium
  • Limitations: special order with surcharge; lining mechanically sensitive to impact

3. PTFE Gasket (all series)

  • Application: seal between viewing disc and body across all GD100 and ASG sight glasses
  • Temperature: up to +240 °C
  • Advantages: near-universal chemical resistance, FDA-compliant, even pressure distribution across the glass
  • Limitations: cold flow under sustained load; replace after every disc change

Glass Materials

1. Borosilicate Glass to DIN 7080

  • Application: steam, aggressive liquids, high temperatures, chemical and pharmaceutical processes; standard viewing disc of the PFA-lined ASG series
  • Temperature: up to +240 °C, very high thermal shock resistance
  • Advantages: low thermal expansion, resistant to thermal shock, high chemical resistance, very clear optical transmission
  • Limitations: not resistant to hydrofluoric acid and hot concentrated alkalis; more impact-sensitive than pressed tempered glass

2. Soda-Lime Tempered Glass

  • Application: water, oils, neutral media, standard applications in building services and mechanical engineering; standard for the GD100 threaded design
  • Temperature: up to +150 °C (application dependent)
  • Advantages: economical standard solution, good optical quality, sufficient strength for common operating pressures
  • Limitations: limited thermal shock resistance, not suitable for aggressive chemicals or high-temperature steam

3. Pressed Tempered Glass

  • Application: mechanically stressed lines, pressure pulses, vibrations, larger nominal sizes; standard for the GD100 flanged design
  • Temperature: up to +240 °C (with PTFE gasket)
  • Advantages: high mechanical strength through pre-stressing, impact-resistant, pressure-resistant up to 16 bar
  • Limitations: lower chemical resistance than borosilicate glass; no post-machining possible

Glass Selection for the Sight Glass at a Glance

The glass type determines the service life and the safety of the sight glass. Temperature, medium and mechanical load therefore decide the correct choice. The following prose overview assigns the three glass materials to their typical applications.

Borosilicate glass to DIN 7080 — up to +240 °C, very high chemical resistance, medium mechanical strength. Standard choice for steam, acids, alkalis, chemical and pharmaceutical media, and the standard disc of the PFA-lined ASG series.

Pressed tempered glass — up to +240 °C, medium chemical resistance, very high mechanical strength. Standard choice for flanged installations, pressure pulses, vibrations and larger nominal sizes; standard disc of the GD100 flanged design.

Soda-lime tempered glass — up to +150 °C, low to medium chemical resistance, medium mechanical strength. Standard choice for water, oils, neutral media in threaded installations; standard disc of the GD100 threaded design.

Do you need a different combination of body, disc and gasket? Fergo also manufactures sight glasses as a special design — with a protective disc, illumination or impact guard. Please contact us through the customised solutions section. Verify material compatibility with your process medium beforehand using the Fergo resistance check.

Certificates & Standards for Sight Glasses

Fergo sight glasses comply with the Pressure Equipment Directive 2014/68/EU and carry the CE mark. Borosilicate viewing discs follow DIN 7080. Flange connections follow DIN 2501 or DIN EN 1092-1 and EN 1092-2, and face-to-face lengths follow EN 558-1 series 1. Threaded connections follow ISO 7-1 and EN 10226-1.

Inspection documents to EN 10204 — type 2.2 works certificate or type 3.1 inspection certificate — are supplied on request. A full overview of all certificates is published on the Fergo certificate page. For steam and condensate systems, the technical sales team can advise on the layout together with GESTRA steam traps for optimum condensate management.

Delivery & Availability

Fergo holds more than 25,000 industrial valves in stock. This includes sight glasses of the GD100 and ASG series in every common nominal size from DN15 up to DN250 — with flange or threaded connection and in three glass variants. Spare glass discs and PTFE gaskets are also kept in stock. Orders are picked the same working day.

Fergo ships across Europe — including the United Kingdom, the Nordic countries and all other EU member states. Smaller threaded sight glasses travel by parcel service, whereas heavy flanged sight glasses go by forwarding agent. Express delivery follows within the next working days. You will find shipping costs, payment options and express terms on the shipping and payment terms page. For special designs or project quantities, please contact us through the customised solutions section.