rotametre

Rotameter, or variable area flowmeter, is a device that measures flow rate by the position of a float inside a tapered tube. Fluid enters at the bottom; as the flow increases, the float rises until drag forces balance weight and buoyancy. The float's height, read against a calibrated scale, indicates volumetric flow for a given fluid density.

Construction and operation: The tube is usually glass or clear plastic, with a freely moving float made of glass, metal, or composite. The system requires vertical orientation and no external power. Readings are direct, but scales may be nonlinear. For gases, readings assume specified conditions; for liquids, density affects the result.

Applications and advantages: Rotameters are simple, robust, inexpensive, and provide immediate in-line flow readings without power. They are common in chemical processing, water treatment, laboratories, and pilot plants. Limitations include modest accuracy, sensitivity to temperature and density changes, and the need to be level and free of air bubbles; not ideal for slurries or very high pressures.

Variants: Glass rotameters and metal variants exist; some designs use alternative float materials or scales, including standard-condition gas scales. Modern versions may couple the float position to an electronic transducer for data acquisition.