All About Rotameter: Simple But Useful Flow Rate Meters
A rotameter, also known as a variable area flow meter, is a device that measures the volumetric flow rate of a fluid. It consists of a tapered tube with a freely moving float inside. The fluid flows upwards through the tapered tube, and the force of the flow pushes the float up. The position of the float within the tube corresponds to the flow rate, which can be read from a scale marked on the side of the tube.