Sight glass window use for autoclaves and other steam applications

January 30, 2013

Tags: autoclaves, duraport fused sight glass, pharmaceutical, sanitary applications, sight glass

Author: Bryan Kim | Google+

Sometimes, large autoclaves are used in applications that require in-situ visual inspections. Since such applications are not very common, a user may find that autoclave manufacturers don't offer suitable sight windows as original features. Adding a window to a modestly pressurized vessel might sound easy enough, but adding windows to a pressurized steam service environment requires additional considerations.

The most important technical consideration for this application is that condensing steam is corrosive towards common silicate glasses; hydroxyl anions from water attack silicon-oxygen bonds in glass (A detailed report on this is available in this PPC white paper). While the rate of corrosion and typical operating pressures are too low to create a catastrophic rupture hazard, the condensing water corrosion will cause the stressed sealing surfaces to develop leaks, and reduce the optical clarity of the glass. This is why steam service glass has to be replaced on a scheduled basis. If possible, consider the following when you choose your steam service sight glass:

  • Plastic lenses do not suffer any water corrosion. Lexan lenses can be used for service up to 250 degrees Fahrenheit, which is typical of autoclave operations.
  • Soda-lime or other silicate glass lenses can be offered with Teflon coatings. While Teflon coatings have a cloudy appearance when dry, even a tiny bit of water condensation will cause the lens to become optically clear. This is always the case in low-temperature steam service.
  • Condensation will occur at typical autoclave conditions; without a wiper, a sight window is often useless.
  • Common glass is perfectly suitable, but will require maintenance and inspections, as well as scheduled replacement. In particular, they will develop leaks. The user will have to reseal leaks properly as they develop.

PPC can help enhance your specialty autoclave, or other steam service vessels, through our wide selection of sight glass windows, making appropriate selections of features needed for this environment. Our sight glasses are particularly well-known for their ease of sealing and resealing, without the need for carefully measured torqueing sequences that have to be used with other sight glass brands.

  • PPC's Model L unit is the perfect sight glass for this application, requiring little maintenance and trivially easy resealing of leaks. They are available in materials that are approved by pharmaceutical industry codes.
  • If the application requires unusually high temperatures and pressures, Model B line is well suited. It offers the same easy resealing as the Model L, but can handle temperatures and pressures that are unrivaled in the industry.

Of the many sight glass windows PresSure Products Company has available, three were designed specifically with pharmaceutical use in mind. If there are industry codes that have to be adhered to with respect to removable fittings, the following products will fit the bill:

  • Types I and II sight glasses have a removable threaded retainer cap, providing easy access to the lens for cleaning and/or product sampling. The bodies and caps of both types are made of stainless steel. The glass is made of tempered soda lime, tempered borosilicate, quartz, polycarbonate, and acrylic. The gaskets are made of Teflon, Viton, Buna-N, silicone, EPDM, and Gore-Tex.
  • The Type III sight glass is designed for use with sanitary applications. It does not need to be welded on; rather, it is affixed with a pharmaceutical tri-clamp that can separate from the unit quickly without the use of tools. This is especially useful for equipment that must be cleaned daily. The cover of this sight glass is made of stainless steel, and the glass is made of tempered soda lime, tempered borosilicate, quartz, polycarbonate, and acrylic. Gaskets are made of Teflon, Viton, Buna-N, silicone, and EPDM.
  • DuraPort fused sight glasses with tri-clamp rims are available. Note that these MUST be ordered with Teflon coating for this application.

For more on PPC's sight glass offerings, please contact our sales engineers at (800) 624-9043.

Bryan Kim, Director of Engineering for PresSure Products Company, can be reached at

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