How does a Rotameter work ?

How a rotameter works...

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. When a rotameter is used with a liquid the float rises because of a combination of the velocity head of the fluid and the buoyancy of the liquid.

With a gas the buoyancy is negligible and the float moves in the most part due to the velocity head of the gas. In both cases, the greater the flow then the higher up the tube the float moves. The float moves up and down the tapered tube in proportion to the flow rate and the annular area between the float and the tapered tube wall. As the float moves up through the tube because of its tapered nature the annular opening increases. As this increases the differential pressure across the float decreases. The float stabilises when the weight of the float is in equilibrium with the upward force being exerted by the fluid or gas.

The float can then be compared to a calibrated scale either printed onto the tube itself or placed next to the tube on the outside of the flow meter. The calibrated scale will commonly give a volumetric flow reading, for example litres per minute (LPM).

Premier Control Technologies offer a complete range of Rotameters.

For more information, please contact :

Premier Control Technologies Ltd.
Unit 1 Oaktree Business Park, Philip Ford Way, Wymondham, Norfolk, NR18 9AQ
+44 (0)1953 609930 (ext 742)

August 2019


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