Sight Glass Windows

PresSure Products Company's sight glasses allow processes within industrial pipes, tanks, and vessels to be observed visually. While most other units consist of a piece of glass sandwiched between two metal flanges, our sight windows are designed to circumvent the significant limitations of such designs, and provide the users with an easily maintained installation that offer large margins of safety.

The majority of our units are Factory Mutual approved, and custom safety sight glasses can be designed to meet your exact specifications.

The following standard models are available for immediate ordering at (800) 624-9043 (click on any listing for a product description, engineering details, materials of construction, and unit image).

Model L Sight Glasses Model L is one of our most economical designs for the majority of sight window applications. Available in 100 or 150 PSI pressure ratings, with a single piece or laminated two piece lens, and with 150 PSI class ANSI B16.5 flange connection or weld pad connection.

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Model B Sight Glasses Model B is the most versatile sight window on the market, capable of addressing higher pressure and temperature requirements that defeat other designs. Available in flange connection (ANSI B16.5 class 150, 300, or even higher, and other custom flanges) or weld pad connection.

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Model I Sight Glasses Model I is an economical design for service in aggressive chemical environments that require very corrosion resistant (and expensive) metals. By incorporating an insert that isolates the wetted area from the bulk of the structural metal, this design minimizes the use of expensive materials while providing the required corrosion resistance performance as well as the high temperature and pressure performance of Model B. Available in flange connection (ANSI B16.5 class 150, 300, or even higher, and other custom flanges) or weld pad connection.

View Model I Sight Glass Catalog >
We offer a variety of other sight window products.
  • X150 our low-cost alternative that retains the technical advantages of our premium offerings.
  • Bull's Eye sight windows are for smaller sizes with essentially unlimited connection options.
  • Oblong windows are for cases that require both the large field of view of a sight window and the vertical span of a level gauge. They are ideal for quickly checking liquid levels AND closely observing the processes inside.
  • Hinged Closure design is a sight window built into a pressure door in order to provide physical access into the process.
  • For sanitary connections, the economical Type III design affords a large view and ease of use, while Type I and II incorporate a threaded cap that allows of easy re-sealing without the need to dissemble the sight window from the process. DuraPort fused sight glasses are available for the same application.
  • Model A is the predecessor of Model B, but it is still available for customers whose pre-existing specifications require them.

Most solid mechanics textbook calculations of sight windows consider only the unsupported diameter, thickness, and mechanical properties of the glass window. In reality, the greatest stresses on the glass do not arise at the center of the unsupported surface; they are usually posed by the sealing gaskets. The gaskets have to undergo some degree of plastic deformation in order to fill in the microscopic crevices in the glass and flange surfaces in order to create an effective seal. In conventional sight glasses that are sandwiched between two flanges, this stress is provided by the bolts of the flanges directed through the planar surfaces of the glass, which usually results in far higher deviatoric (Von Mises) stresses around the sealing gaskets than at the unsupported center of the glass.

With such designs, insufficient torque on the bolts will result in leaks, but excessive torque will cause glass failure. Furthermore, the inherently plastic nature of gaskets will cause them to "cold flow," resulting in leaks that have to be re-sealed by additional torque on the flange bolts. Eventually, it will become impossible to seal the sight window without destroying the glass.

PresSure Products' higher performance sight windows make use of a radial sealing scheme that de-couples the sealing stress on the glass from both the bolt thrust and process pressure. The bolts push down on the packing material place around the side walls of the glass, and the bolt thrust is not directed at any surface of the glass. This scheme reduces the peak deviatoric stress in the glass, and greatly reduces the chances of causing glass damage while sealing the sight window. This unique sealing paradigm also allows the softer high temperature glass to be used in high pressure applications, allowing PresSure Products to offer industry leading combinations of high temperature and high pressure ratings.

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