Which instrument pair is used to measure flow in a piping system?

Which instrument pair is used to measure flow in a piping system?

• A. Pressure gauge and thermometer
• B. Pitot tube and gauge
• C. Flow meter and pressure regulator
• D. Orifice plate and gauge

Answer: (B)

Measuring flow in a piping system comes down to capturing how fast the fluid is moving and turning that speed into a flow rate. A Pitot tube does this by sensing velocity pressure: it points upstream to stop the fluid and measure stagnation pressure, while a separate static-pressure reading gives the reference. The difference between stagnation and static pressure is dynamic pressure, which equals ½ρv². From this, you can solve for the velocity v, and then multiply by the pipe’s cross-sectional area to get the volumetric flow rate (and adjust for density if you need mass flow). This direct relation between velocity pressure and flow makes the Pitot tube paired with a gauge a practical choice for determining how much fluid is moving through a pipe. Other options don’t directly provide flow velocity in the same way. A pressure gauge with a thermometer only tells pressure and temperature, not how fast the fluid is moving. A flow meter with a pressure regulator describes control or indication of flow but isn’t the basic instrument pairing used to derive flow from velocity pressure. An orifice plate with a gauge does measure flow by detecting differential pressure across a restriction to infer flow rate, which is a valid method, but the Pitot tube approach specifically measures velocity through stagnation pressure and translates that into flow.

Measuring flow in a piping system comes down to capturing how fast the fluid is moving and turning that speed into a flow rate. A Pitot tube does this by sensing velocity pressure: it points upstream to stop the fluid and measure stagnation pressure, while a separate static-pressure reading gives the reference. The difference between stagnation and static pressure is dynamic pressure, which equals ½ρv². From this, you can solve for the velocity v, and then multiply by the pipe’s cross-sectional area to get the volumetric flow rate (and adjust for density if you need mass flow). This direct relation between velocity pressure and flow makes the Pitot tube paired with a gauge a practical choice for determining how much fluid is moving through a pipe.

Other options don’t directly provide flow velocity in the same way. A pressure gauge with a thermometer only tells pressure and temperature, not how fast the fluid is moving. A flow meter with a pressure regulator describes control or indication of flow but isn’t the basic instrument pairing used to derive flow from velocity pressure. An orifice plate with a gauge does measure flow by detecting differential pressure across a restriction to infer flow rate, which is a valid method, but the Pitot tube approach specifically measures velocity through stagnation pressure and translates that into flow.