In differential pressure flow measurement, the pressure drop is created by which component?

• A. A smoothing filter
• B. A compressor
• C. A restriction such as an orifice or venturi
• D. A seal

Answer: (C)

The essential idea is that a restricted passage in the flow path creates a measurable pressure difference. When fluid passes through a restriction like an orifice or a Venturi, the flow velocity increases as it squeezes through, and the pressure drops upstream of the restriction while a lower pressure is present downstream. This pressure drop, or differential pressure, is related to the flow rate for a given fluid density and pipe geometry, so sensors placed across the restriction can translate that drop into a flow measurement. A smoothing filter won’t create a pressure difference in the pipe; it only affects the signal. A compressor adds energy to the flow but doesn’t generate the specific local drop used to gauge flow. A seal isn’t part of the flow-measuring path and doesn’t produce the differential pressure used for measurement.