What is a rotameter and how does it work?

A rotameter is a form of variable area flow meter that features a simple float in a vertical tapered tube through which liquid or gas passes. In order for this fluid to pass through the tube it must pass the float, causing it to rise 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 position of 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).

Follow the link to find out more about Premier Control Technologies' complete range of rotameters, or contact the company with any questions or to discuss your application.