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Flow Measurement · Glossary

What is the Vena Contracta?

point of minimum jet areaFlow Measurement

Vena contracta is the point just downstream of an orifice where the jet is narrowest and the pressure is lowest.

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Vena Contracta Explained

After passing an orifice the fluid jet keeps narrowing for a short distance before it spreads to fill the pipe again. At the narrowest point the velocity is highest and the static pressure lowest.

Its position depends on beta ratio, roughly half a pipe diameter downstream. Vena contracta taps placed there give the highest DP, but standard flange, corner and D and D/2 taps are more common.

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Calculators for Vena Contracta

CalculatorOrifice Flow CalculatorFree online calculator with formula and worked example.CalculatorOrifice Pressure Loss CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is the Vena Contracta?

Vena contracta is the point just downstream of an orifice where the jet is narrowest and the pressure is lowest.

Why does the jet keep contracting?

Fluid approaching the plate from the sides cannot turn sharply at the edge, so the jet continues to converge after the bore.

Does cavitation start at the vena contracta?

Yes. It has the lowest pressure, so liquid flashes or cavitates there first if the pressure drops below vapour pressure.

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All flow measurement terms · Full glossary A to Z

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