A rotameter consists of a tapered tube, typically made of glass with a ‘float’ (a shaped weight, made either of anodized aluminum or a ceramic), inside that is pushed up by the drag force of the flow and pulled down by gravity. The drag force for a given fluid and float cross-section is a function of flow speed squared only. The typical application has:
Basic liquid or gas flow measurement
Flow measurement of rotating equipment
Process analyzer
High-pressure flow on the offshore oil rig
Chemical injection
Metering of cleaning liquid or gas
High purity or corrosive liquid
Air samplers and medical application