Flow Measurement · Free Calculator
Averaging Pitot Tube (Annubar Type) Flow Calculator
Convert the DP of an averaging pitot tube (Annubar type) into flow using the sensor flow coefficient K, or find the DP the transmitter will see at your maximum flow.
Averaging pitotFlow coefficient KLow pressure lossDP range
K
Volume flow (actual)3,277.7 m³/h
Mass flow3,933.2 kg/h
Mean velocity17.9 m/s
How this result was calculated
- Q = K × A × √(2ΔP ÷ ρ) = 0.62 × 0.05087 m² × √(2 × 500 ÷ 1.2) = 3,277.7 m³/h
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Averaging Pitot Equation
Q = K × A × √(2 × ΔP ÷ ρ)
ΔP = (ρ ÷ 2) × [Q ÷ (K × A)]²
ΔP = (ρ ÷ 2) × [Q ÷ (K × A)]²
K is the flow coefficient of the sensor (from the manufacturer, depending on sensor type and blockage), A the pipe internal area, ΔP the measured DP and ρ the fluid density at flowing conditions. For gases at significant DP the vendor also applies an expansion factor.
Worked example
Air (1.2 kg/m³) in a 10" Sch 40 duct (254.5 mm) with K = 0.62 at 5 mbar gives about 3,278 m³/h, a mean velocity of 17.9 m/s.
Key insight: averaging pitot tubes have very low permanent pressure loss and can be hot tapped into large lines, but their DP is small, so transmitter range and zero stability matter.
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Frequently Asked Questions
What is an averaging pitot tube?
A probe across the full pipe diameter with several upstream ports that average the velocity profile and a downstream port for the low pressure.
Where does the K factor come from?
From the manufacturer, based on sensor type and the ratio of probe width to pipe diameter.
Why is the DP so low?
It is close to the dynamic pressure of the flow, much smaller than the DP of an orifice at the same flow.
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