Sight glass

In most refrigerant systems sight glass is installed on the liquid line. Sight glass has dual functions: first, ensuring the presence of liquid refrigerant and second, observing the amount of moisture in the system.  That is usually a brass cylinder with a glass eyelet middle of it. Around the glass, there is an indicator that changes color to show the moisture content within the refrigerant.  

How does sight glass works in a refrigeration cycle

During the operation of the refrigeration system, the glass must be clear, and observe no bubbles in the refrigerant flow. That means the refrigerant liquid is subcooled. Otherwise, the presence of bubbles in sight glass indicates there is a problem in the system such as below:

• Lack of refrigerant in the system
• Need to replace filter dryer
• Presence of moisture or non-distillable gas in the system
• Low capacity of the condenser 
• Refrigerant evaporation before the expansion valve

The above cases must be checked with certain tests by an expert person.

Sight glass inlet and outlet connection plugs must not be opened before installation on the line. if not, moisture in the air might change the indicator color permanently. Although in many cases vacuuming the system would change the color into dry mode again. To choose the right sight glass, the type of refrigerant and oil should be considered.

Sight glass work pressure

Sight glass or moisture indicators supply in various working pressure such as: 35, 45, 60 bar and also different flare, solder and saddle type connections for installing on the pipe.