Orifice Plate Bore Sizing Calculator
Size a concentric orifice plate for liquid service. Enter the maximum flow and the DP you want at that flow, and the calculator finds the bore, beta ratio and permanent pressure loss.
- Target mass flow = Q × ρ = 49,910 kg/h
- β is found by iteration so that the ISO 5167-2 flow at 250 mbar equals the target
- Pressure loss ratio Δϖ/ΔP = (√(1 − β⁴(1 − C²)) − Cβ²) ÷ (√(1 − β⁴(1 − C²)) + Cβ²) = 0.623
Orifice Sizing Method
Δϖ ÷ ΔP = (√(1 − β⁴(1 − C²)) − Cβ²) ÷ (√(1 − β⁴(1 − C²)) + Cβ²)
The calculator solves the ISO 5167-2 flow equation for β, recalculating the Reader Harris/Gallagher discharge coefficient and Reynolds number at every step.
Worked example
50 m³/h of water in a 4 inch Sch 40 pipe at 250 mbar maximum DP with flange taps needs a bore of about 61.8 mm (β ≈ 0.60), with a permanent loss of about 62 % of the DP.
Frequently Asked Questions
What DP range should I choose for an orifice plate?
Common ranges are 100 to 500 mbar (40 to 200 inH₂O). Choose one that gives β between about 0.4 and 0.65.
What is permanent pressure loss?
The part of the DP not recovered downstream, roughly (1 − β²) of the DP for an orifice. It costs pumping energy.
Does this work for gas?
This version sizes liquid plates. For gas, also apply the expansibility factor, which the orifice flow calculator includes.
Learn more on the blog
What factors affect the stability of flow meter readings?
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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