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Orifice Plate Flow Calculator

Calculate flow rate, pressure drop, or orifice bore size using ISO 5167 with the Reader-Harris/Gallagher discharge coefficient correlation. Supports liquids and gases.

Geometry
Fluid
Density998.2 kg/m³
Viscosity1.002 cP
Results
Volume flow rate19.84 m³/h
Mass flow rate19803.2 kg/h
Beta ratio (d/D)0.50000
Discharge coeff. (C)0.60711
Approach factor (E)1.03280
Re (pipe)69,917
Pipe velocity0.702 m/s
Orifice velocity2.81 m/s

About Orifice Plate Flow Measurement

An orifice plate is a thin plate with a circular opening (bore) placed in a pipe to create a measurable pressure drop. By measuring the differential pressure across the plate, the flow rate can be calculated using the orifice equation from ISO 5167.

ISO 5167 Orifice Equation

The volumetric flow rate through an orifice plate is:

Q=Cd⋅E⋅ε⋅π4⋅d2⋅2⋅ΔPρQ = C_d \cdot E \cdot \varepsilon \cdot \frac{\pi}{4} \cdot d^2 \cdot \sqrt{\frac{2 \cdot \Delta P}{\rho}}
  • CdC_d — discharge coefficient (Reader-Harris/Gallagher correlation)
  • EE — velocity of approach factor
  • ε\varepsilon — expansibility factor (for compressible fluids)
  • dd — orifice bore diameter
  • ΔP\Delta P — measured differential pressure
  • ρ\rho — fluid density

Discharge Coefficient

The discharge coefficient C accounts for real-flow effects including contraction of the flow stream and viscous losses. This calculator uses the Reader-Harris/Gallagher (2006) correlation, which is the basis of ISO 5167-2. It depends on the beta ratio (d/D), Reynolds number, pipe diameter, and pressure tap arrangement (corner, flange, or D and D/2 taps).

Pressure Tap Types

  • Flange taps — pressure tappings at 25.4 mm (1 inch) from each face of the orifice plate. Most common in North America.
  • Corner taps — tappings at the orifice plate faces (zero distance). Common in Europe.
  • D and D/2 taps — upstream tap at 1D, downstream at 0.5D from the plate.

For pipe pressure drop calculations, use our friction loss calculator. For pipe network simulation with orifice plates, valves, and other components, try SimuPipe.

Frequently Asked Questions

What is the beta ratio and why does it matter?
The beta ratio is the orifice bore diameter divided by the pipe internal diameter (d/D). It determines the restriction severity and affects the discharge coefficient. ISO 5167 is valid for beta ratios between 0.1 and 0.75. Higher beta ratios produce less pressure drop but lower differential pressure signals, making flow measurement less sensitive. Typical flow measurement plates use beta 0.3-0.7.
What is the discharge coefficient (Cd)?
The discharge coefficient accounts for the difference between actual flow and theoretical flow through the orifice. For a sharp-edged orifice plate, Cd is typically 0.59-0.65 depending on beta ratio, Reynolds number, and tap type. This calculator uses the ISO 5167 Reader-Harris/Gallagher (RHG) correlation to compute Cd accurately. Cd is not constant — it varies with flow rate through the Reynolds number dependency.
What are the different orifice tap types?
ISO 5167 defines three standard pressure tap locations: corner taps (at the orifice plate face), flange taps (1 inch from the plate on each side), and D-D/2 taps (one pipe diameter upstream, half a diameter downstream). Flange taps are most common in process industries. The tap location affects the measured differential pressure and the Cd calculation. All three are supported by this calculator.
Can I use an orifice plate for gas flow measurement?
Yes, orifice plates work for both liquids and gases. For gases, the expansibility factor (epsilon) accounts for the density change across the plate. This factor depends on the pressure ratio, beta ratio, and the gas's isentropic exponent (ratio of specific heats). This calculator automatically applies the expansibility correction when gas mode is selected.
What is the permanent pressure loss through an orifice plate?
The permanent pressure loss is always less than the measured differential pressure because some pressure is recovered downstream. The recovery depends on the beta ratio: at beta 0.5, roughly 75% of the differential is permanently lost; at beta 0.7, about 55%. This non-recovered loss is an energy cost of using orifice plates versus other flow measurement devices like venturi tubes (which recover more pressure).

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