Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full - Venturi tubes (ISO 5167-4:2022)

What is ISO 5167-4 - Measurement of fluid flow with venturi tubes about?

This international standard is the fourth in a six-part series on measuring fluid flow using pressure differential devices. ISO 5167-4 deals with venturi tubes and has been revised to implement minor corrections, harmonize changes across the series and achieve consistency with the Guide to Uncertainty of Measurement (GUM).

Who is ISO 5167-4 - Measurement of fluid flow with venturi tubes for?

• Manufacturers of pressure differential devices

• Those working with this equipment in the natural gas industry, from chief mechanical engineer or chief metrologist to operators and technicians

• Anyone measuring other gases or liquids (Newtonian fluids) including e.g. hydrogen or carbon dioxide

What does ISO 5167-4 - Measurement of fluid flow with venturi tubes cover?

This part of ISO 5167 specifies the geometry and method of use (installation and operating conditions) of Venturi tubes when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also provides background information for calculating the flowrate and is applicable in conjunction with the requirements given in BS EN ISO 5167-1.

ISO 5167-4 applies only to Venturi tubes in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. In addition, Venturi tubes can only be used uncalibrated in accordance with this standard within specified limits of pipe size, roughness, diameter ratio and Reynolds number, or alternatively they can be used across their calibrated range.

ISO 5167-4 deals with the three types of classic Venturi tubes:

• “As cast”

• Machined

• Fabricated (also known as “rough-welded sheet-iron”)

NOTE: A Venturi tube consists of a convergent inlet connected to a cylindrical throat which is in turn connected to a conical expanding section called the divergent section (or alternatively the diffuser). Venturi nozzles (and other nozzles) are dealt with in BS EN ISO 5167-3.

ISO 5167-4 is not applicable to the measurement of pulsating flow. It does not cover the use of uncalibrated Venturi tubes in pipes sized less than 50 mm or more than 1 200 mm, or where the pipe Reynolds numbers are below 2 × 105.

In the USA the classic Venturi tube is sometimes called the Herschel Venturi tube.

Why should you use ISO 5167-4 - Measurement of fluid flow with venturi tubes?

• This standard is reliable and proven, describing a robust approach and an enduringly effective framework for measuring fluid flow

• It incorporates revisions that improve, refine, update and future-proof the standard

• In particular the revision includes a new section on calibrating meters so that users now have the option of either using the equations outlined in the standard, or to get a better certainty, the new guidance on calibrating meters

• Use of the standard can improve efficiency and help manage risk

ISO 5167-4 contributes to UN Sustainable Development Goal 7 on affordable and clean energy.

What’s new about ISO 5167-4 - Measurement of fluid flow with venturi tubes?

BS EN ISO 5167-4:2022 is a revision of BS EN ISO 5167-4:2003. The major changes in BS EN ISO 5167-4:2022 are:

1. The use of single pressure tappings on Venturi tubes is permitted
2. The discharge coefficient and uncertainty are given in Clause 5 for a Venturi tube with a machined convergent section for ReD > 106
3. Flow calibration of Venturi tubes is included
4. There is improved wording of the rules for spacing of multiple fittings but no change in actual requirements