Which flow measurement method uses a float to determine flow rate?

• A. Bubbler
• B. Float
• C. Submerged Pressure Transducer
• D. Ultrasonic

Answer: (B)

A float-based flow measurement uses a float inside a tapered tube, known as a rotameter. As liquid flows, it pushes the float upward until the upward drag and buoyancy balance the forces on the float. The tube’s narrow-to-wide shape means the float rises higher as flow increases. A calibrated scale on the tube lets you read the flow rate directly from the float’s vertical position. This method is simple, typically does not require power, and provides a direct indication of flow.

Other methods measure level or distance in different ways: a bubbler uses air pressure to infer level, a submerged pressure transducer measures static pressure to gauge level, and ultrasonic devices use sound to determine surface distance. None of these present flow rate as a direct reading from a float in a tapered tube.