What is the primary purpose of a rotameter?

The primary purpose of a rotameter is to measure the flow of gases and liquids. A rotameter uses a float within a tapered tube; as fluid flows through the tube, the float rises to a position that balances the weight of the float and the upward force created by the flow of fluid. The height of the float within the tube indicates the flow rate due to the known relationship between flow rate and float position. This design allows for a visual measurement of the flow, which can be directly correlated to a calibrated scale on the rotameter.

The other options refer to functions that are not performed by a rotameter; for instance, measuring temperature requires different devices such as thermometers or thermocouples, while controlling pressure involves pressure regulators and relief valves. Storing liquid samples is not the function of a rotameter as it is specifically designed to facilitate flow measurement, not storage, thereby reinforcing its primary purpose.