C274 – ISO 5167 Sizing Calculation


This calculates the flow element size of various differential pressure based flow meters according to the ISO 5167 technical standard.


ISO 5167: Measurement of fluid flows by means of pressure differential devices inserted in circular cross-section conduits running full

ISO TR9464: Guidelines for the use of ISO 5167

BS1042: Part 1. Pressure differential devices – Section 1.2 Specification for square-edged orifice plates and nozzles (with drain holes, in pipes below 50mm diameter, as inlet and outlet devices) and other orifice plates and Borda inlets (1984)

24509-54 – Flow Calculations for the V-Cone and Wafer-Cone Flow meters – McCrometer

24517-16 – V-Cone Flow Meter Technical Brief – McCrometer

Kelton calculation reference C274

Kelton calculation C270 – ISO 5167 Orifice Mass Flow Calculation

Kelton calculation C271 – ISO 5167 Venturi Mass Flow Calculation

Kelton calculation C272 – Cone Mass Flow Calculation

Kelton calculation C276 – ISO 5167-5:2016 Cone Mass Flow Calculation


Meter Type

  • Orifice
  • Venturi
  • V-Cone
  • Wafer-Cone
  • Cone (ISO 5167-5)

This option group allows selection of the meter type that the sizing calculation is to be performed on.

Standard version

Allows user to select from different revisions of the standard being applied.


  • Gas
  • Liquid

This option allows selection of whether the fluid in question is a liquid or a gas.

Expansibility factor

  • User entered
  • Calculated

This option give the choice of calculating expansibility or entering a known value when the fluid is a gas.

For an orifice plate

Tapping Type

  • Flange
  • D/D2
  • Corner

This option group allows the selection of the tapping type used for the pressure measurements on the orifice plate system.

Drain Hole

  • None
  • BS 1042

This option allows for selection of a drain hole correction according to BS 1042.

For venturi tubes and cones

Discharge coefficient

  • User entered
  • Variable with Reynold’s number
  • Classical venturi with ‘as cast’ convergent section
  • Classical venturi with rough-welded convergent section
  • Classical venturi with a machined convergent section
  • Venturi nozzle
  • Uncalibrated Cone

This option allows the user to choose how discharge coefficient will be determined for a venturi tube. If a cone meter is selected only the first two options will be available for selection.

Exit cone angle

  • 15°

This option determines the equation used to calculate the permanent pressure loss associated with a venturi.


Sizing Calculation

The orifice bore and venturi throat diameter are related to the diameter of the piping in the equation:

For cone meters the relationship is as follows:

d = Flow element diameter
D = Pipe diameter

The following relationships are applied in an iterative loop to solve for the flow element diameter at operating temperature.

For an orifice plate:

For a venturi tube:

For V-cones and Wafer-cones:

In these equations X is calculated by:

D = Pipe diameter
Δp = Differential pressure
ρ1 = Upstream density
Cd = Discharge coefficient
ε = Expansibility factor
μ1 = Dynamic viscosity
Re = Reynold’s number
qm = Mass flowrate

A temperature correction is then made to calculate the size of the flow element diameter at calibration temperature:

T1 = Upstream temperature
Tdc = Calibration temperature of the flow element
αd = Thermal expansion coefficient of flow element

If a drain hole needs to be taken into account, orifice bore is calculated iteratively by employing a root finding algortihm around the equation:

dr = Drain hole diameter
du = Orifice bore at calibrated temperature
d = Orifice bore corrected for operating temperature
Ctd = Temperature correction



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