Optical Transmission of Sight Glasses

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We had a request from the Georgia Institute of Technology to find out how clear the fused sight glasses really are.

Sight glasses

Sight glasses are some of the products are available in the Encole catalog. These are really cool products because they allow you to see into strange uninhabitable worlds, where pressures and temperatures are high and the air is not air at all but rather a chemically aggressive gas (or liquid).

Well, we did a test and found that fused sight glasses are clear enough to see colors behind them, or liquid levels. One particular type of fused sight glass is super clear, good enough to see all details behind the glass without any distortion. We also found out how much light energy is transferred through the glass, and we wrote a White Paper on the subject: Sight Glass Transmission Curve Test Report. This was a fun project for us engineers, perhaps a bit boring for non-engineers. This is why we placed this particular post in the Product Reviews category. We promise to write about more exciting stuff in future posts. Speaking of the future posts, I think one post a week, preferably on a regular basis, say by every Monday morning would be a reasonable frequency of blog writing.

Here are some images for comparison of various types of fused sight glasses.

NPT-threaded sight glass, 1-inch. Full glass vs. partial glass comparison.

On the left of the picture is a sight glass where the glass partially fills the height of the internal bore of the NPT fitting. Notice how the colors and the lines are a bit distorted by the non-flat nature of fused glass. On the right of the same picture is a sight glass where the glass extends to both top and bottom of the fitting. The glass is lapped and chemically polished on both sides, providing a non-distorted and clear view. Nice!

Sight glass top view, fully glass height


Top view of the fused sight glass where the glass is flush with the top of the metal housing.

Sight glass bottom view, fully glass height


Same product, bottom view. Here, notice how the glass is also flush with the bottom side of the metal housing. For reference, technical information is available about these product.

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