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Control Valve · Glossary

What is Flashing?

liquid turning to vapourControl Valve

Flashing is when liquid partly turns to vapour across a valve because the outlet pressure stays below its vapour pressure.

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Flashing Explained

The two phase mixture leaves the valve at high velocity and erodes trim and downstream pipe with a smooth, polished pattern.

Flashing cannot be stopped by trim design if the system pressure is below vapour pressure. Use hard trim, angle valves discharging into a larger pipe, and size for choked flow.

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Calculators for Flashing

CalculatorCavitation Index CalculatorFree online calculator with formula and worked example.CalculatorValve Outlet Velocity CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Flashing?

Flashing is when liquid partly turns to vapour across a valve because the outlet pressure stays below its vapour pressure.

How do I tell flashing damage from cavitation?

Flashing leaves smooth, shiny erosion; cavitation leaves rough, cinder like pitting.

Does flashing limit flow?

Yes, the flow chokes and further reduction of outlet pressure does not increase it.

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