Rota Meter / Flow Meter

A Rotameter is a form of variable area flow meter which has a simplistic operation whereby a liquid or gas passes through a tapered tube. In order for this gas to pass through the tube it must first raise a float held within the tube. A rotameter consists of a tapered tube, typically made of glass with a 'float'. The drag force for a given fluid and float cross section is a function of flow speed squared only.

Floats are made in many different shapes, with spheres and ellipsoids being the most common. The float may be diagonally grooved and partially colored so that it rotates axially as the fluid passes. The "float" must not float in the fluid: it has to have a higher density than the fluid, otherwise it will float to the top even if there is no flow.

The mechanical nature of the measuring principle provides a flow measurement device that does not require any electrical power. This capability has considerably expanded the range of applications for the variable area flowmeter, since the measurement can observed remotely from the process or used for automatic control.