C273 – ISO 5167 Differential Pressure Calculations


This calculates the differential pressure settings for orifice plates, venturi and cone based metering systems.


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

ISO TR9464: Guidelines for the use of ISO 5167

ISO TR15377: Measurement of fluid flow by means of pressure differential devices – Guidelines for the specification of orifice plates, nozzles and venturi tubes beyond the scope of ISO 5167 (2007)

BS 1042: 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 C273


Meter Type

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

This option group allows the selection of the meter type the calculation is to be carried out on. From this there will be meter specific options for discharge coefficient for venturis and cone meters, and for orifice plates there will be the option for a drain hole correction and the selection of the type of pressure tappings in use on the meter.

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 and also the last one if it is a Cone metered in line with ISO 5167-5.


Differential Pressure

The differential pressure is calculated by rearranging the mass flow equation to zero and solving for differential pressure using an iterative root finding method.



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