Metal fused sight glasses

Conventional sight glasses (DIN 7080, 7081, 8903) are sensitive to stress, bending and mechanical overloading; they might suddenly burst. If this occurs during installation, this results in little cost and inconvenience. If the glass cracks when a plant is fully operational, it may lead to major cost and safety faillures.

Metal fused sight glasses consist – in accordance with DIN 7079 standard – of a round sight glass sealed in a metal ring. The different thermal expansion coefficients of glass and metal result in a homogeneous state of compressive stress in the entire glass body. Therefore metal fused sight glass is a very tough material, based on the principle of “first leak before break”.

This glass is resistant to temperatures of (-60° C) -30° C to + 280° C (+ 300° C) depending on the materials.


  • Security: normal thermally hardened sight glasses may abruptly begin to crack and should be replaced immediately. Metal fused sight glass may also crack, but due to the wedging in the metal ring, the glass remains in place. Damage can be recognized in time and the glass can be replaced when normal maintenance is scheduled.
  • Cost reduction through design solutions, trouble free installation (glass will not break by over tighten the bolts).
  • Cleaning, cavity-free / residual fluid space.


  • For installation in a sight glass or sight flow glass, in severe stress on block flange neck and neck welding instead of a sight glass in accordance with DIN 28121, on flanges according to ANSI, in sterile technical areas, in tanks and in-line housing parts.
  • In mining, for example: (EEX) Explosion-proof lamps etc.
  • In high voltage equipment, power plants, refrigeration industry, high pressure systems.

With very dangerous substances metal fused sight glasses are preferred over thermally toughened borosilicate sight glass or soda-lime glass (IGR 70-0099).


  • Materials: C22.8, 1.0570, 1.4462, 1.4523, 2.4602, 2.4605, 2.4610, 2.4819, 2.4816.
  • Glass quality: Borosilicate glass to DIN 7079 / DIN 7080 and DIN 8901 soda.
  • Pressure: 64 bar (TÜV test certificate for pressure vessel) or up to 1000 bar, depending on the materials and construction.
  • Available with wiper, in tri-clamp, threaded, for installation in existing sight glass fitting DN 15-200 etc.