Rotameter is also known as variable area flow meter.

The instruments used to measure the liquid or gas volumetric flow rate as either a liquid or gas passes through a tapered tube.

A rotameter can be used for purge applications to keep process lines clear. In simple flow measurement, an alarm or an electrical output makes it possible to check flow conditions and control them continuously.

A rotameter contains a transparent, tapered, vertical tube with a small diameter at the bottom. This tube changes its cross-sectional area in order to affect the float by giving it a constant drop.

A Glass tube rotameter are extensively used in industrial areas, laboratories, and other pilot plants. Borosilicate glass is usually used to make the tube. To resist corrosion, the float is manufactured with stainless steel, glass, or plastic.