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A sight glass, also called inspection glass, sight port or sight windows is described as a window in a pipe, or sidewalls of boilers, tanks, process chambers or silos for visually observing the presence, flow or the level of a medium. With this you can check / inpect a device or the entire process.

The weld-in Sight glasses consist generally of a stainless steel or steel base flange (block flange, welding flange) and a deck flange, two seals and glass. The flanges are assembled by means of bolts to each other.

The Sight glass in the pipe (inline mounting) can be supplied with different process connections such as flanges, threaded connection or weld connections.

The glass is chosen depending on the pressure, temperature and the medium and is often one of the two most widely used glasses, borosilicate glass or soda lime glass. Based on these date Ebora can let you calculate the minimum thickness of the glass.

Please keep in mind that, contrary to common belief, every sight glass is subject to wear.Lens and sealing gaskets should be replaced periodically before there is an obvious sign of degradation. We therefore recommend that you regularly check the glass and always order spare glass and seals with your sight glas.

If the security can be compromised, you can always use double glazing. With double glazed glass is always selected so that it can withstand all the pressure. For aggressive media or steam, we recommend adding mica disks to protect the glass.

Transparent media are more difficult to observe. The following can be done. In the rectangular sight glasses you often use reflex glass in these cases. This is a glass with ridges on the inside. The refractive index of the medium than even makes the clear media visible. In the other sight glasses they often use a flap, ball or imppeller (rotor) in order to show the flow of the clear, transparent media.

A sight glass can also be carried out with lighting in order to be able to look better in the tank or pipe.

Ebora is a major player in the field of sight glasses and has divided them into the following four main groups.

  • Round sight glasses
  • Rectangular sight glasses
  • Oval sight glasses
  • Flow sight glasses

The range includes sight glass from vacuum to high pressure and / or temperature applications.

When the medium causes deposition in the sight glass we can provide a wiper or spraying nozzle. These chaoice of these options we need to know before order because the glass needs to be adapted. The same for lighting, because then the flange needs additional holes for mounting.

Installation guideline:

After welding the base flange onto/into the pressure vessel, the sealing surface must be checked for deformations! Reworking may be required!

The operating pressure does not relate to the base flange! The base flange must be audited according to AD 2000 guidelines together with the pressure vessel!

For sight glass lighting and custom work please contact us on +31 (0) 26-3706830 or