Pipe flow calculators

Orifice plate calculator


Calculator Description

This calculator can be used for calculating of actual flow rate through orifice plate flow meter, for measured pressure drop and can also be used for orifice plate sizing.

  • Calculate:

    • Flow rate for known orifice size and pressure difference
    • Flow velocity in the orifice throat
    • Discharge coefficient for compressible flow
    • Gas expansion coefficient for compressible flow
  • Input:

    • Pressure difference in front and after the orifice plate
    • Orifice plates diameters
    • Density
    • Viscosity

Calculator Features

  • Conversion between volumetric and weight flow rate
  • Calculation of Reynolds number included
  • Applicable for non-compressible liquids and compressible perfect gases
  • For pressure measuring position in terms of corner taps, 1 inch taps and also D & D/2 taps
  • For single-phase fluid, subsonic, non-pulsating flow
  • ISO 5167 based calculation

Orifice plate is very practical and relatively low-cost measuring device for flow rate measurement with good accuracy. By placing orifice plate in the pipe, sudden pressure drop is created. Degree of created pressure drop is directly proportional to the stream velocity and consequently, to the flow rate. That behavior and strong interaction between stream velocity and pressure drop due to local restrictions is used for flow rate measurement by orifice plate.

Flow rate measuring with orifice plate is not as easy as with some other more advanced measuring equipment. In order to get good, accurate measuring results, orifice plate should be manufactured and positioned in the pipeline strictly according to relevant standard like ISO 5167. When all standard requirements are met, measuring results can be trusted.

With this calculator you can calculate actual flow rate for measured pressure difference in front and after the orifice plate. Equations used in this calculator are in accordinance with ISO 5167. Calculated flow rate is provided on the actual conditions – actual absolute pressure and temperature.

As calculation is based on the Bernoulli principle and energy equation, you can use this calculator for other purposes other than just for flow rate measurement. In that case you should uncheck option to use ISO 5167 constraints in the calculator itself.

For compressible gas flow through orifice, expansion factor is calculated and made known during the process of calculation. Its value is calculated based on the equation provided in ISO 5167. The value of expansion factor depends on the flowing gas specific heat ratio (Cp/Cv), orifice diameter ratio (d1/d2) and pressures in front and after the orifice.

Another coefficient, discharge coefficient, is also calculated and made known, and that coefficient is determined using Reader-Harris/Gallagher (1998) equation (ISO 5167). Discharge coefficient is referencing orifice diameter ratio (d1/d2), Reynolds number (Re) and pressure measuring taps position (corner taps, D & D/2 taps or 1" taps).

Limits of use for orifice plates with a corner and D and D/2 tappings:

  • d > 12.5 mm
  • 50 mm < D < 1000 mm
  • 0.1 < β < 0.75
  • ReD > 5000 for 0.1 < β < 0.56
  • ReD > 16000xβ2 for β > 0.56

Limits of use for orifice plates with flange tappings:

  • d > 12.5 mm
  • 50 mm < D < 1000 mm
  • 0.1 < β < 0.75
  • ReD > 5000 and ReD > 170xβ2xD

Please tell me what do you think about this calculator

If you would like to use the calculator, but actually can't see the blue CALCULATOR button in the upper left part of the page than please read instructions.

Q: Calculate flow rate of air flowing through orifice plate with external diameter of 200 mm and internal diameter of 100 mm, at 288 K. Measured pressures in front and after the orifice is 104000 Pa and 100000 Pa. Pressure is measured on corner taps.

A: Calculation setup:
Flowing fluid: gas
Input one from following two:
p2 - absolute pressure after the orifice
T - temperature
ni - kinematic viscosity
Enter values:
D1 = 200 mm
D2 = 100 mm
p1 = 104000 Pa (absolute)
p2 = 100000 Pa (absolute)
ni = 13.4 mm2/s
T = 288 K
R = 287 J/kgK
kappa = 1.4
select tap type - corner taps

Q: Calculate flow rate of water flowing through orifice plate with external diameter of 120 mm and internal diameter of 80 mm. Measured pressures in front and after the orifice is 11000 mm of water column Pa and 10000 mm of water column. Pressure is measured on 1 inch taps

A: Calculation setup:
Flowing fluid: liquid
Input one from following two:
p2 - absolute pressure after the orifice
ni - kinematic viscosity
Enter values:
D1 = 120 mm
D2 = 80 mm
p1 = 11000 mmWS (absolute)
p2 = 10000 mmWS (absolute)
ni = 1.006 mm2/s
rho = 1000 kg/m3
select tap type - 1 inch taps

Q: Calculate flow rate of water through orifice with external diameter of 200 mm, internal diameter of 160 mm. Measured pressure drop in front of orifice is 10729 mmWS and measured pressure drop is 400 mmWS.

A: Calculation setup:
Flowing fluid: liquid
Input one from following two:
p1 - p2 - measured pressure drop
T - temperature
ni - kinematic viscosity
Enter values:
D1 = 200 mm
D2 = 160 mm
p1 = 10729 mmWS (absolute)
p1 - p2 = 400 mmWS (absolute)
ni = 1.006 mm2/s
rho = 1000 kg/m3
select tap type - corner taps

Equation used for flow through orifice plate calculation

Read more about used theory on flow in valves and fittings page.

If you experience problems with calculator start try to find answers on instructions page.

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