Liquid level measurement

Constant and accurate measuring

A bubble tube system is a simple, accurate, reliable and a low cost method of measuring liquid level in an open or a vented tank.

A low but constant flow of air or an inert gas is purged through a dip tube of which the open end is located near the bottom of the tank. The flow needs to be just enough to overcome the hydrostatic pressure produced by the liquid level and to release a constant stream of bubbles from the open end of the dip tube.

As long as the flow remains constant and uninterrupted the liquid level in the tank is proportional to the pressure inside the dip tube. A low cost pressure or a differential pressure transmitter is used to detect the variation in this pressure giving an accurate liquid level reading.

A water purge is used instead of air in level measurements of higher consistency mediums or contaminated liquids (e.g. pulp level in pump stand pipes).