A little movement is normal, but a glass bouncing several inches points to foaming, oil in a new boiler, priming from sudden load swings, or a firing rate too high for the boiler's steam space. It can also mean a partly blocked glass connection. Operators treat it as a reason to check water chemistry and load before the low-water cutoff starts tripping on the dips.
Bouncing glass, two inches every time it fires, new boiler and still oily, we need to skim it.
Also heard as
- bouncing water line
Related terms
Gauge glass
The glass tube or window on a steam boiler that shows the operator the actual water level.
Foaming
A stable layer of bubbles on the boiler water surface that makes level hard to read and carries water out with the steam.
Priming
Sudden surges that throw slugs of boiler water out with the steam.
Low-water cutoff
A safety control that shuts the burner off when the boiler water level drops below a safe point.