Valve Outlet Velocity Calculator
High outlet velocity causes noise, erosion and vibration in control valves. Check liquid velocity, or gas velocity and Mach number at outlet conditions.
- v = Q ÷ A = 5.526 m/s
Outlet Velocity
Gas: v = ṁ ÷ (ρ2 A), Mach = v ÷ √(γ R T ÷ M)
Common guidelines: liquid outlet velocity below about 10 m/s (lower for erosive or flashing service), gas outlet Mach below about 0.3 for low noise and 0.5 as an upper limit.
Worked example
100 m³/h of water through an 80 mm outlet runs at 5.5 m/s. 5000 kg/h of air at 3 bar(a) and 30 °C through the same outlet reaches about Mach 0.23.
Frequently Asked Questions
What is the maximum velocity in a control valve outlet?
About 10 m/s for clean liquids and Mach 0.3 to 0.5 for gases are typical design limits, but check the valve manufacturer’s guidance.
Why is gas velocity calculated at outlet pressure?
Gas expands as pressure falls, so velocity is highest at the outlet where density is lowest.
Does pipe velocity matter too?
Yes. Downstream pipe velocity also generates noise, and reducers right after the valve can raise velocity further.
Learn more on the blog
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