SIST EN ISO 5167-2:2004
(Main)Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full - Part 2: Orifice plates (ISO 5167-2:2003)
Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full - Part 2: Orifice plates (ISO 5167-2:2003)
ISO 5167-2:2003 specifies the geometry and method of use (installation and operating conditions) of orifice plates when they are inserted in a conduit running full to determine the flow-rate of the fluid flowing in the conduit.
It also provides background information for calculating the flow-rate and is applicable in conjunction with the requirements given in ISO 5167-1.
ISO 5167-2:2003 is applicable to primary devices having an orifice plate used with flange pressure tappings, or with corner pressure tappings, or with D and D/2 pressure tappings. Other pressure tappings such as vena contracta and pipe tappings have been used with orifice plates but are not covered by ISO 5167-2:2003.
ISO 5167-2:2003 is applicable only to a flow which remains subsonic throughout the measuring section and where the fluid can be considered as single phase. It is not applicable to the measurement of pulsating flow. It does not cover the use of orifice plates in pipe sizes less than 50 mm or more than 1 000 mm, or for pipe Reynolds numbers below 5 000.
Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit Kreisquerschnitt - Teil 2: Blenden (ISO 5167-2:2003)
Dieser Teil von ISO 5167 legt die geometrischen Formen und Maße sowie die Anwendung (Einbau- und Betriebsbedingungen) von Blenden, die in einer voll durchströmten Rohrleitung zur Bestimmung des Durchflusses eingebaut sind, fest.
Dieser Teil von ISO 5167 enthält grundlegende Informationen für die Durchflussberechnung und ist gemeinsam mit den in ISO 5167-1 festgelegten Anforderungen anzuwenden.
Das in diesem Teil von ISO 5167 behandelte Primärgerät ist eine Blende mit Flansch-Druckentnahmen, Eck- Druckentnahmen oder D- und D/2-Druckentnahmen. Andere Druckentnahmen, wie z. B. Vena-Contracta- und beliebige Druckentnahmen im Rohr, werden im Zusammenhang mit Blenden zwar verwendet, sind jedoch nicht Gegenstand dieser Norm. Dieser Teil von ISO 5167 gilt nur für eine Strömung, die im gesamten Messquerschnitt im Unterschallbereich liegt und wo das Fluid als einphasig betrachtet werden kann. Dieser Teil von ISO 5167 gilt nicht für Messungen bei pulsierenden Strömungen, für Rohrdurchmesser kleiner als 50 mm oder größer als 1 000 mm und für (rohrbezogene) Reynolds-Zahlen unter 5 000.
Mesure de débit des fluides au moyen d'appareils déprimogenes insérés dans des conduites en charge de section circulaire - Partie 2: Diaphragmes (ISO 5167-2:2003)
L'ISO 5167-2:2003 spécifie la géométrie et le mode d'emploi (conditions d'installation et d'utilisation) de diaphragmes insérés dans une conduite en charge dans le but de déterminer le débit du fluide s'écoulant dans cette conduite.
L'ISO 5167-2:2003 fournit également des informations de fond nécessaires au calcul de ce débit, et il convient de l'utiliser conjointement avec les exigences stipulées dans l'ISO 5167-1.
L'ISO 5167-2:2003 est applicable aux éléments primaires équipés d'un diaphragme utilisé avec des prises de pression à la bride ou des prises de pression dans les angles ou des prises de pression à D et à D/2. D'autres prises de pression, telles que des prises de pression «vena contracta» ou des prises de tuyauterie ont été utilisées avec des diaphragmes, mais ne sont pas traités dans l'ISO 5167-2:2003.
L'ISO 5167-2:2003 est applicable uniquement à un écoulement qui reste subsonique dans tout le tronçon de mesurage et où le fluide peut être considéré comme monophasique. Elle n'est pas applicable au mesurage d'un écoulement pulsé. Elle ne couvre pas l'utilisation de diaphragmes dans des conduites de diamètre inférieur à 50 mm ou supérieur à 1 000 mm, ni pour des nombres de Reynolds rapportés au diamètre de la conduite inférieurs à 5 000.
Merjenje pretoka fluida na osnovi tlačne razlike, povzročene z napravo, vstavljeno v polno zapolnjen vod s krožnim prerezom – 2. del: Zaslonke (ISO 5167-2:2003)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 5167-2:2004
01-januar-2004
1DGRPHãþD
SIST EN ISO 5167-1:1997
SIST EN ISO 5167-1:1997/A1:2001
0HUMHQMHSUHWRNDIOXLGDQDRVQRYLWODþQHUD]OLNHSRY]URþHQH]QDSUDYRYVWDYOMHQR
YSROQR]DSROQMHQYRGVNURåQLPSUHUH]RP±GHO =DVORQNH ,62
Measurement of fluid flow by means of pressure differential devices inserted in circular
cross-section conduits running full - Part 2: Orifice plates (ISO 5167-2:2003)
Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit
Kreisquerschnitt - Teil 2: Blenden (ISO 5167-2:2003)
Mesure de débit des fluides au moyen d'appareils déprimogenes insérés dans des
conduites en charge de section circulaire - Partie 2: Diaphragmes (ISO 5167-2:2003)
Ta slovenski standard je istoveten z: EN ISO 5167-2:2003
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
SIST EN ISO 5167-2:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 5167-2:2004
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SIST EN ISO 5167-2:2004
EUROPEAN STANDARD
EN ISO 5167-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2003
ICS 17.120.10 Together with EN ISO 5167-1:2003,
EN ISO 5167-3:2003 and EN ISO 5167-4:2003,
supersedes EN ISO 5167-1:1995
English version
Measurement of fluid flow by means of pressure differential
devices inserted in circular cross-section conduits running full -
Part 2: Orifice plates (ISO 5167-2:2003)
Mesure de débit des fluides au moyen d'appareils Durchflussmessung von Fluiden mit Drosselgeräten in voll
déprimogènes insérés dans des conduites en charge de durchströmten Leitungen mit Kreisquerschnitt - Teil 2:
section circulaire - Partie 2: Diaphragmes (ISO 5167- Blenden (ISO 5167-2:2003)
2:2003)
This European Standard was approved by CEN on 20 February 2003.
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 Management Centre 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovak Republic, 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
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 5167-2:2003 E
worldwide for CEN national Members.
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SIST EN ISO 5167-2:2004
EN ISO 5167-2:2003 (E)
CORRECTED 2003-09-03
Foreword
This document (EN ISO 5167-2:2003) 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 September 2003, and conflicting national
standards shall be withdrawn at the latest by September 2003.
This document, together with EN ISO 5167-1:2003, EN ISO 5167-3:2003 and EN ISO 5167-4:2003,
supersedes EN ISO 5167-1:1995.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and the
United Kingdom.
Endorsement notice
The text of ISO 5167-2:2003 has been approved by CEN as EN ISO 5167-2:2003 without any
modifications.
NOTE Normative references to International Standards are listed in Annex ZA (normative).
2
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SIST EN ISO 5167-2:2004
EN ISO 5167-2:2003 (E)
Annex ZA
(normative)
Normative references to international publications
with their relevant European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE Where an International Publication has been modified by common modifications, indicated by
(mod.), the relevant EN/HD applies.
Publication Year Title EN Year
ISO 4006 1991 Measurement of fluid flow in closed EN 24006 1993
conduits - Vocabulary and symbols
ISO 5167-1 1991 Measurement of fluid flow by means of EN ISO 5167-1 1995
pressure differential devices - Part 1:
Orifice plates, nozzles and Venturi
tubes inserted in circular cross-section
conduits running full
3
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SIST EN ISO 5167-2:2004
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SIST EN ISO 5167-2:2004
INTERNATIONAL ISO
STANDARD 5167-2
First edition
2003-03-01
Measurement of fluid flow by means of
pressure differential devices inserted in
circular-cross section conduits running
full —
Part 2:
Orifice plates
Mesure de débit des fluides au moyen d'appareils déprimogènes
insérés dans des conduites en charge de section circulaire —
Partie 2: Diaphragmes
Reference number
ISO 5167-2:2003(E)
©
ISO 2003
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
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ii © ISO 2003 — All rights reserved
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
4 Principles of the method of measurement and computation. 2
5 Orifice plates . 2
5.1 Description. 2
5.2 Pressure tappings. 6
5.3 Coefficients and corresponding uncertainties of orifice plates. 10
5.4 Pressure loss, ∆ϖ.13
6 Installation requirements . 15
6.1 General. 15
6.2 Minimum upstream and downstream straight lengths for installation between various
fittings and the orifice plate . 15
6.3 Flow conditioners . 20
6.4 Circularity and cylindricality of the pipe. 26
6.5 Location of orifice plate and carrier rings. 27
6.6 Method of fixing and gaskets . 28
Annex A (informative) Tables of discharge coefficients and expansibility [expansion] factors. 29
Annex B (informative) Flow conditioners. 41
Bibliography . 46
© ISO 2003 — All rights reserved iii
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(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 5167-2 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits,
Subcommittee SC 2, Pressure differential devices.
This first edition of ISO 5167-2, together with the second edition of ISO 5167-1 and the first editions of
ISO 5167-3 and ISO 5167-4, cancels and replaces the first edition of ISO 5167-1:1991, which has been
technically revised, and ISO 5167-1:1991/Amd.1:1998.
ISO 5167 consists of the following parts, under the general title Measurement of fluid flow by means of
pressure differential devices inserted in circular-cross section conduits running full :
Part 1: General principles and requirements
Part 2: Orifice plates
Part 3: Nozzles and Venturi nozzles
Part 4:Venturi tubes
iv © ISO 2003 — All rights reserved
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
Introduction
ISO 5167, consisting of four parts, covers the geometry and method of use (installation and operating
conditions) of orifice plates, nozzles and Venturi tubes when they are inserted in a conduit running full to
determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the
flowrate and its associated uncertainty.
ISO 5167 (all parts) is applicable only to pressure differential devices in which the flow remains subsonic
throughout the measuring section and where the fluid can be considered as single-phase, but is not applicable
to the measurement of pulsating flow. Furthermore, each of these devices can only be used within specified
limits of pipe size and Reynolds number.
ISO 5167 (all parts) deals with devices for which direct calibration experiments have been made, sufficient in
number, spread and quality to enable coherent systems of application to be based on their results and
coefficients to be given with certain predictable limits of uncertainty.
The devices introduced into the pipe are called “primary devices”. The term primary device also includes the
pressure tappings. All other instruments or devices required for the measurement are known as “secondary
1)
devices”. ISO 5167 (all parts) covers primary devices; secondary devices will be mentioned only occasionally.
ISO 5167 consists of the following four parts.
a) ISO 5167-1 gives general terms and definitions, symbols, principles and requirements as well as methods
of measurement and uncertainty that are to be used in conjunction with ISO 5167-2, ISO 5167-3 and
ISO 5167-4.
b) ISO 5167-2 specifies orifice plates, which can be used with corner pressure tappings, D and D/2 pressure
2)
tappings , and flange pressure tappings.
3)
c) ISO 5167-3 specifies ISA 1932 nozzles , long radius nozzles and Venturi nozzles, which differ in shape
and in the position of the pressure tappings.
4)
d) ISO 5167-4 specifies classical Venturi tubes .
Aspects of safety are not dealt with in Parts 1 to 4 of ISO 5167. It is the responsibility of the user to ensure
that the system meets applicable safety regulations.
___________________________
1) See ISO 2186:1973, Fluid flow in closed conduits — Connections for pressure signal transmissions between primary
and secondary elements.
2) Orifice plates with “vena contracta” pressure tappings are not considered in ISO 5167.
3) ISA is the abbreviation for the International Federation of the National Standardizing Associations, which was
succeeded by ISO in 1946.
4) In the USA, the classical Venturi tube is sometimes called the Herschel Venturi tube.
© ISO 2003 — All rights reserved v
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SIST EN ISO 5167-2:2004
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SIST EN ISO 5167-2:2004
INTERNATIONAL STANDARD ISO 5167-2:2003(E)
Measurement of fluid flow by means of pressure differential
devices inserted in circular-cross section conduits running
full —
Part 2:
Orifice plates
1 Scope
This part of ISO 5167 specifies the geometry and method of use (installation and operating conditions) of
orifice plates when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in
the conduit.
This part of ISO 5167 also provides background information for calculating the flowrate and is applicable in
conjunction with the requirements given in ISO 5167-1.
This part of ISO 5167 is applicable to primary devices having an orifice plate used with flange pressure
tappings, or with corner pressure tappings, or with D and D/2 pressure tappings. Other pressure tappings
such as “vena contracta” and pipe tappings have been used with orifice plates but are not covered by this part
of ISO 5167. This part of ISO 5167 is applicable only to a flow which remains subsonic throughout the
measuring section and where the fluid can be considered as single phase. It is not applicable to the
measurement of pulsating flow. It does not cover the use of orifice plates in pipe sizes less than 50 mm or
more than 1 000 mm, or for pipe Reynolds numbers below 5 000.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 4006:1991, Measurement of fluid flow in closed conduits — Vocabulary and symbols
ISO 5167-1:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular-cross
section conduits running full — Part 1: General principles and requirements
3 Terms, definitions and symbols
For the purposes of this document, the terms, definitions and symbols given in ISO 4006 and ISO 5167-1
apply.
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
4 Principles of the method of measurement and computation
The principle of the method of measurement is based on the installation of an orifice plate into a pipeline in
which a fluid is running full. The presence of the orifice plate causes a static pressure difference between the
upstream and downstream sides of the plate. The mass flowrate, q , can be determined using Equation (1):
m
C π
2
qd= ε 2∆pρ (1)
m
1
4 4
1−β
The uncertainty limits can be calculated using the procedure given in Clause 8 of ISO 5167-1:2003.
Computation of the mass flowrate, which is a purely arithmetic process, can be performed by replacing the
different terms on the right hand side of the basic Equation (1) by their numerical values.
Similarly, the value of volume flowrate, q , is calculated from:
V
q
m
q = (2)
V
ρ
where ρ is the fluid density at the temperature and pressure for which the volume is stated.
As will be seen later in this part of ISO 5167, the coefficient of discharge, C, is dependent on the Reynolds
number, Re, which is itself dependent on q , and has to be obtained by iteration (see Annex A of
m
ISO 5167-1:2003 for guidance regarding the choice of the iteration procedure and initial estimates).
The diameters d and D mentioned in the formula are the values of the diameters at working conditions.
Measurements taken at any other conditions should be corrected for any possible expansion or contraction of
the orifice plate and the pipe due to the values of the temperature and pressure of the fluid during the
measurement.
It is necessary to know the density and the viscosity of the fluid at the working conditions. In the case of a
compressible fluid, it is also necessary to know the isentropic exponent of the fluid at working conditions.
5 Orifice plates
NOTE 1 The various types of standard orifice meters are similar and therefore only a single description is needed.
Each type of standard orifice meter is characterized by the arrangement of the pressure tappings.
NOTE 2 Limits of use are given in 5.3.1.
5.1 Description
5.1.1 General
The axial plane cross-section of a standard orifice plate is shown in Figure 1.
The letters given in the following text refer to the corresponding references in Figure 1.
5.1.2 General shape
5.1.2.1 The part of the plate inside the pipe shall be circular and concentric with the pipe centreline. The
faces of the plate shall always be flat and parallel.
5.1.2.2 Unless otherwise stated, the following requirements apply only to that part of the plate located
within the pipe.
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
5.1.2.3 Care shall be taken in the design of the orifice plate and its installation to ensure that plastic
buckling and elastic deformation of the plate, due to the magnitude of the differential pressure or of any other
stress, do not cause the slope of the straight line defined in 5.1.3.1 to exceed 1 % under working conditions.
NOTE Further information is given in 8.1.1.3 of ISO/TR 9464:1998.
Key
1 upstream face A
2 downstream face B
a
Direction of flow.
Figure 1 — Standard orifice plate
5.1.3 Upstream face A
5.1.3.1 The upstream face A of the plate shall be flat when the plate is installed in the pipe with zero
differential pressure across it. Provided that it can be shown that the method of mounting does not distort the
plate, this flatness may be measured with the plate removed from the pipe. Under these circumstances, the
plate may be considered to be flat when the maximum gap between the plate and a straight edge of length D
laid across any diameter of the plate (see Figure 2) is less than 0,005(D – d)/2, i.e. the slope is less than
0,5 % when the orifice plate is examined prior to insertion into the meter line. As can be seen from Figure 2,
the critical area is in the vicinity of the orifice bore. The uncertainty requirements for this dimension can be met
using feeler gauges.
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
Key
1 orifice plate outside diameter
2 pipe inside diameter (D)
3 straight edge
4 orifice
5 departure from flatness (measured at edge of orifice)
Figure 2 — Orifice plate-flatness measurement
−4
5.1.3.2 The upstream face of the orifice plate shall have a roughness criterion Ra < 10 d within a circle
of diameter not less than D and which is concentric with the orifice. In all cases, the roughness of the
upstream face of the orifice plate shall not be such that it affects the edge sharpness measurement. If, under
working conditions, the plate does not fulfil the specified conditions, it shall be repolished or cleaned to a
diameter of at least D.
5.1.3.3 Where possible, it is useful to provide a distinctive mark which is visible even when the orifice
plate is installed to show that the upstream face of the orifice plate is correctly installed relative to the direction
of flow.
5.1.4 Downstream face B
5.1.4.1 The downstream face B shall be flat and parallel with the upstream face (see also 5.1.5.4).
5.1.4.2 Although it may be convenient to manufacture the orifice plate with the same surface finish on
each face, it is unnecessary to provide the same high quality finish for the downstream face as for the
upstream face (see Reference [1]; but also see 5.1.9).
5.1.4.3 The flatness and surface condition of the downstream face may be judged by visual inspection.
5.1.5 Thicknesses E and e
5.1.5.1 The thickness e of the orifice shall be between 0,005D and 0,02D.
5.1.5.2 The difference between the values of e measured at any point on the orifice shall not be greater
than 0,001D.
5.1.5.3 The thickness E of the plate shall be between e and 0,05D.
However, when 50 mm u D u 64 mm, a thickness E up to 3,2 mm is acceptable.
It shall also meet the requirements of 5.1.2.3.
5.1.5.4 If D W 200 mm, the difference between the values of E measured at any point of the plate shall
not be greater than 0,001D. If D < 200 mm, the difference between the values of E measured at any point of
the plate shall not be greater than 0,2 mm.
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
5.1.6 Angle of bevel α
5.1.6.1 If the thickness E of the plate exceeds the thickness e of the orifice, the plate shall be bevelled on
the downstream side. The bevelled surface shall be well finished.
5.1.6.2 The angle of bevel α shall be 45° ± 15°.
5.1.7 Edges G, H and I
5.1.7.1 The upstream edge G shall not have wire-edges or burrs.
5.1.7.2 The upstream edge G shall be sharp. It is considered so if the edge radius is not greater than
0,000 4d.
If d W 25 mm, this requirement can generally be considered as satisfied by visual inspection, by checking that
the edge does not reflect a beam of light when viewed with the naked eye.
If d < 25 mm, visual inspection is not sufficient.
If there is any doubt as to whether this requirement is met, the edge radius shall be measured.
5.1.7.3 The upstream edge shall be square; it is considered to be so when the angle between the orifice
bore and the upstream face of the orifice plate is 90° ± 0,3°. The orifice bore is the region of the orifice plate
between edges G and H.
5.1.7.4 The downstream edges H and I are within the separated flow region and hence the requirements
for their quality are less stringent than those for edge G. This being the case, small defects (for example, a
single nick) are acceptable.
5.1.8 Diameter of orifice d
5.1.8.1 The diameter d shall in all cases be greater than or equal to 12,5 mm. The diameter ratio, β = d/D,
shall be always greater than or equal to 0,10 and less than or equal to 0,75.
Within these limits, the value of β may be chosen by the user.
5.1.8.2 The value d of the diameter of the orifice shall be taken as the mean of the measurements of at
least four diameters at approximately equal angles to each other. Care shall be taken that the edge and bore
are not damaged when making these measurements.
5.1.8.3 The orifice shall be cylindrical.
No diameter shall differ by more than 0,05 % from the value of the mean diameter. This requirement is
deemed to be satisfied when the difference in the length of any of the measured diameters complies with the
said requirement in respect of the mean of the measured diameters. In all cases, the roughness of the orifice
bore cylindrical section shall not be such that it affects the edge sharpness measurement.
5.1.9 Bidirectional plates
5.1.9.1 If the orifice plate is intended to be used for measuring reverse flows, the following requirements
shall be fulfilled:
a) the plate shall not be bevelled;
b) the two faces shall comply with the specifications for the upstream face given in 5.1.3;
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SIST EN ISO 5167-2:2004
ISO 5167-2:2003(E)
c) the thickness E of the plate shall be equal to the thickness e of the orifice specified in 5.1.5; consequently,
it may be necessary to limit the differential pressure to prevent plate distortion (see 5.1.2.3);
d) the two edges of the orifice shall comply with the specifications for the upstream edge specified in 5.1.7.
5.1.9.2 Furthermore, for orifice plates with D and D/2 tappings (see 5.2), two sets of upstream and
downstream pressure taps shall be provided and used according to the direction of the flow.
5.1.10 Material and manufacture
The plate may be manufactured from any material and in any way, provided that it is and remains in
accordance with the foregoing description during the flow measurements.
5.2 Pressure tappings
5.2.1 General
For each orifice plate, at least one upstream pressure tapping and one downstream pressure tapping shall be
installed in one or other of the standard locations, i.e. as D and D/2, flange or corner tappings.
A single orifice plate may be used with several sets of pressure tappings suitable for different types of
standard orifice meters, but to avoid mutual interference, several tappings on the same side of the orifice plate
shall be offset by at least 30°.
The location of the pressure tappings characterizes the type of standard orifice meter.
5.2.2 Orifice plate with D and D/2 tappings or flange tappings
5.2.2.1 The spacing l of a pressure tapping is the distance between the centreline of the pressure tapping
and the plane of a specified face of the orifice plate. When installing the pressure tappings, due account shall
be taken of the thickness of the gaskets and/or sealing material.
5.2.2.2 For orifice plates with D and D/2 tappings (see Figure 3), the spacing l of the upstream pressure
1
tapping is nominally equal to D, but may be between 0,9D and 1,1D without altering the discharge coefficient.
The spacing l of the downstream pressure tapping is nominally equal to 0,5D but may be between the
2
following values without altering the discharge coefficient:
between 0,48D and 0,52D when β u 0,6;
between 0,49D and 0,51D when β > 0,6.
Both l and l spacings are measured from the upstream face of the orifice plate.
1 2
5.2.2.3 For orifice plates with flange tappings (see Figure 3), the spacing l of the upstream pressure
1
tapping is nominally 25,4 mm and is measured from the upstream face of the orifice plate.
The spacing l' of the downstream pressure tapp
...
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