A rotameter works by the use of a float located in a tube, through which flows a particular substance. The float, which is denser than the substance, determines the flow rate by rising and resting at a precise level in the tube as the substance flows through.
The force of gravity pulls the float downward as the force of the flowing substance pulls it upward. A vertical measuring tube is required as a rotameter is gravity-dependent. A constant flow and specific temperature of the substance are also required to keep the float in one position and enable the determination of the flow rate of the liquid or gas.
The tube of a rotameter is scaled and made of glass or transparent material in order to establish the position of the float. Rotameters are reliable for particular substances at particular temperatures, but several rotameters have to be used to measure different substances.
Rotameters are used in systems such as oil pipelines to measure the flow rate of oil as it flows from one location to another. Portable rotameters are also used to determine the flow rate of large bodies of gas or liquid, such as the atmosphere, rivers, oceans and streams.