liminfoOrifice Flow Calculator
Free web tool: Orifice Flow Calculator
Details
About Orifice Flow Calculator
The Orifice Flow Calculator implements the ISO 5167 standard for measuring fluid flow through orifice plates in circular pipes. It uses the Reader-Harris/Gallagher discharge coefficient correlation, which iterates over the Reynolds number to converge on an accurate Cd value. Inputs include pipe diameter, orifice diameter, differential pressure across the orifice, and fluid density. The tool supports three standard pressure tap configurations: flange taps (25.4 mm from the orifice face), corner taps (at the orifice face), and D and D/2 taps (one pipe diameter upstream and half a diameter downstream).
Process engineers, instrumentation engineers, and plant operators use this tool to design and verify orifice metering installations. The beta ratio (d/D) is a critical design parameter — ISO 5167 recommends values between 0.20 and 0.75 for reliable measurement, and the calculator flags beta ratios outside this range with a warning. Output includes the volumetric flow rate in both m³/h and L/min, the velocity approach factor E, pipe and orifice velocities, Reynolds number, and estimated permanent pressure loss — all essential for sizing orifice plates and associated instrumentation.
All calculations run entirely in the browser using an iterative algorithm that converges within 20 iterations for typical flow conditions. No server call is made and no data is stored. The tool is designed for quick pre-engineering estimates and educational demonstration of differential pressure flowmeter principles, not as a substitute for a full engineering calculation package or certified metering design software.
Key Features
- ISO 5167 compliant calculation using the Reader-Harris/Gallagher Cd correlation with Reynolds number iteration
- Three pressure tap configurations: flange taps, corner taps, and D and D/2 taps
- Outputs volumetric flow rate in both m³/h and L/min for easy cross-reference
- Reports beta ratio (d/D), discharge coefficient Cd, and velocity approach factor E
- Calculates pipe velocity, orifice throat velocity, and pipe Reynolds number
- Estimates permanent pressure loss across the orifice plate
- Warns when beta ratio is outside the ISO 5167 recommended range of 0.20 to 0.75
- 100% client-side iterative calculation — no server required, works on any device
Frequently Asked Questions
What is an orifice plate flow meter?
An orifice plate is a thin disc with a precisely machined hole (orifice) inserted in a pipeline. As fluid passes through the restriction, the velocity increases and static pressure drops. By measuring this differential pressure and applying the ISO 5167 equations, the volumetric or mass flow rate can be determined.
What is the beta ratio and why does it matter?
The beta ratio (β) is the ratio of the orifice diameter (d) to the pipe internal diameter (D): β = d/D. It directly affects the discharge coefficient and the magnitude of the differential pressure signal. ISO 5167 recommends β values between 0.20 and 0.75. Values outside this range may produce inaccurate discharge coefficients or impractically small/large differential pressures.
What discharge coefficient correlation does this calculator use?
The calculator uses a simplified version of the Reader-Harris/Gallagher (RHG) correlation, which is the basis for ISO 5167-2. It accounts for the beta ratio and Reynolds number, and includes tap-location correction terms for flange and D/D2 taps. The correlation converges iteratively because Cd depends on Reynolds number, which itself depends on flow rate.
What is the difference between flange, corner, and D/D2 taps?
Flange taps are located 25.4 mm (1 inch) upstream and downstream of the orifice plate face, which is the most common installation in industry. Corner taps are located at the orifice face itself, typically used for smaller bore pipes. D and D/2 taps are located one pipe diameter upstream and half a pipe diameter downstream, offering different pressure recovery characteristics.
What fluid density should I use for water?
The default density in the calculator is 998 kg/m³, which corresponds to liquid water at approximately 20°C. For other temperatures or fluids, use the appropriate density: seawater is approximately 1025 kg/m³, air at standard conditions is about 1.2 kg/m³, and light oils typically range from 800 to 900 kg/m³.
What is permanent pressure loss and how is it calculated?
Permanent pressure loss is the irrecoverable pressure drop caused by the orifice plate — the portion of differential pressure that does not recover downstream. The calculator uses the approximate formula for pressure loss based on the beta ratio. This is important for energy cost analysis and system pressure budget calculations.
Is this calculator suitable for gas flow measurement?
The calculator assumes an incompressible fluid (constant density), which is accurate for liquids. For gases, compressibility effects become significant when the differential pressure exceeds about 5% of the absolute upstream pressure. For compressible gas flow, an expansibility factor must be applied — this is not currently included in the calculator.
What does it mean when the beta ratio warning appears?
The yellow warning indicates that the orifice-to-pipe diameter ratio is outside the ISO 5167 recommended range of 0.20 to 0.75. Below 0.20, the orifice is very small relative to the pipe and may produce a very high differential pressure. Above 0.75, the discharge coefficient correlation becomes less reliable. In both cases, the calculated flow rate should be treated with caution.