EN ISO 9300:2005

SLOVENSKI STANDARD
01-november-2005
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SIST EN ISO 9300:1998
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Measurement of gas flow by means of critical flow Venturi nozzles (ISO 9300:2005)
Durchflussmessung von Gasen mit Venturidüsen bei kritischer Strömung (ISO
9300:2005)
Mesure de débit de gaz au moyen de Venturi-tuyeres en régime critique (ISO
9300:2005)
Ta slovenski standard je istoveten z: EN ISO 9300:2005
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 9300
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2005
ICS 17.120.10 Supersedes EN ISO 9300:1995
English Version
Measurement of gas flow by means of critical flow Venturi
nozzles (ISO 9300:2005)
Mesure de débit de gaz au moyen de Venturi-tuyères en Durchflussmessung von Gasen mit Venturidüsen bei
régime critique (ISO 9300:2005) kritischer Strömung (ISO 9300:2005)
This European Standard was approved by CEN on 15 July 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9300:2005: E
worldwide for CEN national Members.

Foreword
This document (EN ISO 9300:2005) has been prepared by Technical Committee ISO/TC 30
"Measurement of fluid flow in closed conduits" in collaboration with CMC.

This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by February 2006, and conflicting national
standards shall be withdrawn at the latest by February 2006.

This document supersedes EN ISO 9300:1995.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Endorsement notice
The text of ISO 9300:2005 has been approved by CEN as EN ISO 9300:2005 without any
modifications.
INTERNATIONAL ISO
STANDARD 9300
Second edition
2005-08-15
Measurement of gas flow by means of
critical flow Venturi nozzles
Mesure de débit de gaz au moyen de Venturi-tuyères en régime
critique
Reference number
ISO 9300:2005(E)
©
ISO 2005
ISO 9300:2005(E)
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ii © ISO 2005 – All rights reserved

ISO 9300:2005(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Terms and definitions. 1
2.1 Pressure measurement . 1
2.2 Temperature measurement. 2
2.3 Venturi nozzles. 2
2.4 Flow. 2
3 Symbols . 5
4 Basic equations . 6
4.1 State equation . 6
4.2 Flow-rate under ideal conditions . 6
4.3 Flow-rate under real conditions . 6
4.4 Critical mass flux . 7
5 Applications for which the method is suitable . 7
6 Standard critical flow Venturi nozzles (CFVN).7
6.1 General requirements. 7
6.2 Design . 8
7 Installation requirements . 11
7.1 General. 11
7.2 Upstream pipeline. 11
7.3 Large upstream space. 12
7.4 Downstream requirements . 12
7.5 Pressure measurement . 12
7.6 Drain holes . 13
7.7 Temperature measurement. 13
7.8 Density measurement. 13
7.9 Calculated density . 14
8 Calculation methods. 14
8.1 Mass flow-rate. 14
8.2 Discharge coefficient, C . 14
d′
8.3 Critical flow function, C , and real gas critical flow coefficient, C . 15
∗ R
8.4 Conversion of measured pressure and temperature to stagnation conditions. 15
8.5 Maximum permissible downstream pressure. 16
9 Uncertainties in the measurement of flow-rate . 17
9.1 General. 17
9.2 Practical computation of uncertainty . 18
Annex A (normative) Venturi nozzle discharge coefficients . 19
Annex B (normative) Tables of values for critical flow function C — Various gases. 21
∗
Annex C (normative) Computation of critical mass flux for natural gas mixtures. 28
Annex D (normative) Mass flow correction factor for atmospheric air . 32
Annex E (normative) Computation of critical mass flux for critical flow nozzles with high nozzle
throat to upstream pipe diameter ratio, β > 0,25. 33
Bibliography . 36

ISO 9300:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 9300 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits,
Subcommittee SC 2, Pressure differential devices.
This second edition cancels and replaces the first edition (ISO 9300:1990), which has been technically revised.

iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 9300:2005(E)

Measurement of gas flow by means of critical flow Venturi
nozzles
1 Scope
This International Standard specifies the geometry and method of use (installation in a system and operating
conditions) of critical flow Venturi nozzles (CFVN) used to determine the mass flow-rate of a gas flowing
through a system. It also gives the information necessary for calculating the flow-rate and its associated
uncertainty.
It is applicable to Venturi nozzles in which the gas flow accelerates to the critical velocity at the throat (this
being equal to the local sonic velocity), and only where there is steady flow of single-phase gases. At the
critical velocity, the mass flow-rate of the gas flowing through the Venturi nozzle is the maximum possible for
the existing upstream conditions while CFVN can only be used within specified limits, e.g. Iimits for the nozzle
throat to inlet diameter ratio and throat Reynolds number. This International Standard deals with CFVN for
which direct calibration experiments have been made in sufficient number to enable the resulting coefficients
to be used with certain predictable limits of uncertainty.
Information i
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