Sight Glass
          For Compressed Air

A sight glass can be used in many applications and in many industries. They will all have to do with the fact that it is necessary to visually monitor the level of a liquid inside a container with container walls that you cannot see through. Here is more information about sight glasses.

In compressed air applications, usually the sight-glass is used on the outside of an opaque compressed air filter bowl or a lubricator bowl. The link takes you to an information page on this site about air filters.

A sight-glass will be plumbed vertically alongside the outside of the bowl or the tank or whatever vessel is being level-monitored. It will be installed with an inlet into the sight-glass through the wall at the bottom of the vessel, and another near the top.

Sight Glass

The drawing shows the sight-glass installed on the left side of the filter bowl.

For clarity, my drawing shows the sight-glass standing-off the bowl. Different manufacturers have different style sight-glasses, with some being completely attached to the side of the bowl, and some are stand-off designs, where the sight glass doesn't touch the bowl except where the lines penetrate the bowl surface at the top and the bottom.

It is called a sight-glass since the original sight glass was made of ... glass - for best visibility, of course.

Today sight-glass materials used in compressed air applications are more likely to be a synthetic plastic or composite that offers the clarity of glass, but without the same potential for breakage.