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Venturi meter
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Flow speed from pressure difference between wide and narrow sections.
A pipe with a narrow throat; the pressure difference between wide and narrow sections gives the flow speed: v₁ = A₂√(2ΔP/ρ(A₁² − A₂²)).
Used for measuring flow in pipes and carburettors.
Needs calibration for real fluids.
In more detail
A Venturi meter measures flow rate by measuring pressure difference across a constriction. The narrowed section speeds the flow and lowers the pressure, which reveals the flow speed.
Real-world uses
- Water and gas flow meters in pipelines use Venturi tubes.
- Carburettors use the Venturi effect to mix fuel and air.
- Engineers measure the flow in a pipe by fitting a Venturi meter and recording the pressure drop across the narrow section.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why is there a pressure drop?
Because the flow speeds up in the narrow section, and Bernoulli's principle lowers the pressure there.
Is energy lost?
Some energy is lost to turbulence, but the device is designed to be efficient.
Why does the pressure drop in the narrow section?
The fluid speeds up, so Bernoulli's principle says the pressure falls where the speed is higher.
Related topics in Fluids & Elasticity
Bernoulli's principle · Applications of Bernoulli · Torricelli's theorem · Pitot tube · Lift on a wing · Magnus effect