How does a differential pressure (DP) flowmeter operate?

• A. It introduces a constriction in the pipe that creates a pressure drop across the flowmeter, and the drop increases with flow.
• B. It uses ultrasonic waves to determine flow velocity.
• C. It relies on a turbine wheel to measure flow.
• D. It measures density to infer flow rate.

Answer: (C)

A differential pressure flowmeter works by placing a restriction in the pipe, such as an orifice plate, venturi, or flow nozzle. As the fluid flows through that restriction, it speeds up and the pressure drops from upstream to downstream. The difference in pressure (ΔP) across the restriction is related to how much fluid is moving through the pipe. By measuring that ΔP with pressure taps and applying a calibration that depends on the restriction geometry and fluid density, you can calculate the flow rate. In short, the meter converts a pressure difference caused by a constriction into a flow rate: higher flow yields a larger pressure drop.

Other methods described are different technologies. Ultrasonic meters use sound waves to gauge velocity; turbine meters rely on a rotating wheel driven by the flow; measuring density alone doesn’t give flow rate without additional information.