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What is A Sight Glass

What is Sight Glass

A sight glass is a device to observe material conditions inside containers and equipment. It is a safety accessory and should be checked regularly. They are divided by shape into a round and rectangular sight glasses. They are divided into peep sight and illuminated sight glasses according to their use. According to the structure, they are divided into sight glasses with and without lining, neck, cover, double safety, insulation, scraper, and flushing device suitable for powder material.

What is The working principle of Sight Glass?

The sight glass is mainly made up of sight glass bottom panel, the sight glass and the valve components.

The sight glass has a small installation size and a low driving torque. It is easy and quick to operate and has good flow regulation and sealing characteristics. The sight glass is suitable for use in large to medium diameter, low to medium pressure areas and is the dominant form of the sight glass. There are two main categories of valve sight glasses. They are pipe sight glasses and equipment sight glasses.

You can use sight glasses in chemical towers high in temperature, corrosive, poisonous, dangerous, and prone to crystallization. It is to ensure their safe production.

What are the technical parameters of Sight Glass?

Window material

Tempered borosilicate glass, quartz glass

Nuts and bolts

20# 304 304L 316 316L

Sealing gaskets

Buna-N gaskets / PTFE gaskets / metal gaskets / graphite gaskets

Sealing surfaces


Flange Standard


Manufacturing testing standard


Operating temperature

Carbon Steel: -30°C ~ +350°C Stainless Steel: -80°C ~ +480°C

Glass temperature resistance

Tempered polysilicate glass: ≤180°C, silica glass. 1000°C

Glass pressure resistance

Toughened borosilicate glass sheet: ≤3.0MPa

Quartz glass sheet: ≤10.0MPa

Toughened borosilicate glass cylinder: Quartz glass cylinder.


Carbon steel: anti-corrosion paint 

Stainless steel: Pickling treatment or anti-corrosion paint

Structural Drawing of Sight Glass

Structural of sight glass

Dimension of Sight Glass

What are the classifications of sight glasses?

The sight glass is an essential accessory for observing media flow in the pipeline. You can use it in petroleum, chemical, chemical fiber, pharmaceutical, food, and other industrial production installations. It can observe the flow reaction of liquid, gas, steam, and other media at any time. The sight glass is mainly composed of sight glass base plate, sight glass, fasteners, seal assembly, etc. The sight glass can be principally divided into straight-through sight glass, impeller sight glass, float sight glass, etc.

How to install and use the sight glass?

  1. The welded flange must be clean, undamaged, and operated by a professional.
  2. Ensure that the sight glass holder is flat and smooth and that the gasket between the lens and the sight glass holder is installed smoothly. The gasket must be undamaged and free from grease. Ensure that the sight glass and cover are fitted correctly before tightening the screws, then tighten the screws slowly.
  3. The sight glass must work within the permissible pressure range. Otherwise, we cannot guarantee a safe operation. The high allowable temperature for soda-lime glass is 150°C, with a sharp change in temperature ranging from 120°C to 20°C. Toughened borosilicate glass has a high permissible temperature of 280°C and a range of rapid temperature changes from 230°C to 20°C. The high acceptable temperature for quartz glass is 800°C, ranging from 500°C to 20°C for rapid temperature changes. (If none of the above temperatures can be used, please contact us)
  4. You can wipe it lightly with an appropriate amount of alcoholic cotton on its surface before use. Be careful not to use acidic liquids for cleaning as they may erode the outer surface of the glass.
  5. Do not use excessive force or force when installing. It is recommended that the screws are locked diagonally with even strength.
  6. After installing the mirror glass, you must inspect it regularly. Especially in the liquid environment containing acid and alkali, it is necessary to do an excellent job of regular inspection of the glass surface by the degree of corrosion. It will ensure the safety of the front-line operators.

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