Enter the pipe bore, orifice bore and measured ΔP — get the flow rate (or size the bore for a target flow) per ISO 5167.
Open the free calculator →A concentric orifice plate creates a pressure drop that is a known function of flow. Measure the differential pressure across it and you can back out the flow rate — the basis of most industrial flow measurement. This tool inverts the ISO 5167 relation both ways: ΔP → flow, or target flow → bore.
Q = Cd · ε · A₂ · √(2·ΔP/ρ) / √(1 − β⁴)
where Cd is the discharge coefficient (ISO 5167 Reader-Harris/Gallagher), ε the expansibility factor (1 for incompressible liquids, <1 for gases), A₂ the orifice bore area, ΔP the differential pressure, ρ the upstream density, and β = d/D the bore-to-pipe diameter ratio.
The 1/√(1 − β⁴) factor corrects for the fact that the upstream velocity is not negligible when the bore is a large fraction of the pipe.
Design vs measurement: use it to size a metering orifice for a target ΔP transmitter range, or to read flow from field ΔP — with the discharge coefficient computed properly, not assumed at 0.61.
| Input | Value |
|---|---|
| Pipe internal diameter, D | 100 mm |
| Orifice bore, d | 50 mm (β = 0.5) |
| Differential pressure, ΔP | 25 kPa |
| Fluid density | 1000 kg/m³ (water) |
| Discharge coefficient, Cd | 0.605 |
Result: A₂ = 1.963×10⁻³ m²; Q = 0.605 × 1.963e-3 × √(2×25000/1000) / √(1 − 0.5⁴) ≈ 0.0086 m³/s ≈ 31 m³/h. Try it with your own numbers →
Q = Cd·ε·A₂·√(2ΔP/ρ)/√(1−β⁴) — the ISO 5167 orifice equation, with Cd from β and Reynolds number.
Most designs use β = 0.2–0.6; ISO 5167 concentric plates are valid roughly 0.1–0.75.
Orifice flow is one of EnggiBasis' instrumentation tools — free to try, full suite in Pro (₹99/month).
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