There are a couple of reasons you may find yourself needing to know how to install a circular sight glass.

You may have recently installed a new pipe that requires a sight glass. Alternatively, you may need to replace an old one. Over time, your circular sight glass will become clouded, making it hard to see the water level in the pipe, or thin, which is a sign of an impending crack or break. Both are points at which you should replace the sight glass.

When it comes to installing a circular sight glass, the process is crucial to prevent breakage and ensure a secure fit within its fittings. In our latest video, “Circular Sight Glass Installation” we guide you through the procedure and discuss the types of circular sight glass suitable for your needs. Don’t miss out on this informative guide — click play to learn the best practices for a safe and successful installation.

In this article, we will explain what types of circular sight glass you can use, and how to safely install one.


What Are The Types Of Circular Sight Glass?

There are three main types of circular sight glass that we sell at Zight.


 1. Borosilicate Flat Sight Glass Standard DIN7080

This type is made from tempered borosilicate glass. “Tempered” sight glass refers to the process of thermally treating the material so that it becomes stronger and more resilient. These are important qualities for a circular sight glass.


2. Tempered Soda Lime Sight Glass

This type is made from tempered soda lime. It’s a less expensive option than a borosilicate sight glass and works just as well, providing it’s not exposed to food, drugs, chemicals, or temperatures above 300 degrees Fahrenheit.


Flat 3. Quartz Sight Glass

Quartz sight glasses can withstand heat up to 1000 degrees F and thermal shock up to 280 degrees F. They’re quite a bit more expensive than tempered borosilicate or tempered lime soda sight glasses, but they hold up well in extreme applications.

The type you will need depends on factors like budget, application, and manufacturer requirements. Read the manual for your circular sight glass carefully to make sure you choose the correct replacement.

If you choose a borosilicate or lime soda glass, always look for glass that adheres to the DIN international standard for sight glass production, to ensure the highest safety and quality. At Zight, all our borosilicate and soda lime glasses adhere to DIN 7080. You can rely on them to stand up to their rated temperature and pressure limits for a long time without needing to be replaced.

Circular Sight Glasses

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What Do I Need To Install Circular Sight Glass?

Before you begin the process of installing a circular sight glass, make sure you have these necessary supplies on hand:


  • Wrench
  • Torque wrench
  • Sight glass plate (tempered borosilicate, tempered soda lime, or quartz)
  • Rubber gaskets
  • Protective gloves
  • Protective eyewear
  • Set of gaskets for the sight glass


How To Install Circular Sight Glass

To install a circular sight glass, follow these basic steps.


Step 1: Disassemble The Sight Glass

First, you’ll need to disassemble the sight glass. Begin this step after the pipe you’re working on is empty of its contents.

Loosen the screws of the cover flanges, working crosswise to loosen each one at an equal rate. Once the screws are loosened, remove them along with the cover flange, the gasket, the circular sight glass plate, and the second gasket.


Step 2: Clean The Seating Surfaces And Check For Damage

The next step is to clean the seating surfaces – the gaskets and both flanges (the cover and the base, which is still fitted onto the pipe). Make sure they’re free of debris, dirt, and grime. It may be best to go ahead and replace the gaskets at this point to ensure they are strong.

You should also check all the components of the sight glass for damage, like erosions, grooves, or dents. If you find defects on any of the pieces, they will need to be replaced before you install the new sight glass.


Step 3: Reassemble The Sight Glass

Now, reassemble the sight glass, laying a new gasket seal down on the base flanges, followed by the circular sight glass plate, the second gasket, and finally, the cover flanges. Take a few moments to ensure that all the layers are aligned with one another and that you can clearly see through the glass plate to the other side.


Step 4: Tighten The Screws On The Flanges

Tighten the screws on the flanges that same way you loosened them: working crosswise so that they all tighten at an equal rate. Use a torque wrench and tighten each screw at the same torque to prevent the unequal pressure from shattering the glass plate.


Step 5: Check Screws And Fittings After Pipe Resumes Operating Pressure

The final step is to resume operating pressure in the pipe and check the screws on the fittings. They may need to be tightened after being exposed to the increase in pressure.

That’s all there is to it! You have now successfully installed a circular sight glass into its fittings.



Installing a new circular sight glass is not difficult, as long as you follow the right steps for maximum safety and success. You’ll be pleased with the result of your efforts when your DIN 7080 sight glass is properly installed and enabling you to work with optimum efficiency.