EN ISO 5167-3:2003

SLOVENSKI STANDARD
01-januar-2004
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SIST EN ISO 5167-1:1997
SIST EN ISO 5167-1:1997/A1:2001
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Measurement of fluid flow by means of pressure differential devices inserted in circular
cross-section conduits running full - Part 3: Nozzles and Venturi nozzles (ISO 5167-
3:2003)
Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit
Kreisquerschnitt - Teil 3: Düsen und Venturidüsen (ISO 5167-3:2003)
Mesure de débit des fluides au moyen d'appareils déprimogenes insérés dans des
conduites en charge de section circulaire - Partie 3: Tuyeres et Venturi-tuyeres (ISO
5167-3:2003)
Ta slovenski standard je istoveten z: EN ISO 5167-3:2003
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 5167-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2003
ICS 17.120.10 Together with EN ISO 5167-1:2003,
EN ISO 5167-2:2003 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 3: Nozzles and Venturi nozzles (ISO 5167-3:2003)
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 3:
section circulaire - Partie 3: Tuyères et Venturi-tuyères Düsen und Venturidüsen (ISO 5167-3:2003)
(ISO 5167-3:2003)
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, Slovakia, 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 5167-3:2003 E
worldwide for CEN national Members.

CORRECTED  2003-09-03
Foreword
This document (EN ISO 5167-3:2003) 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 5167-2:2003 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 5167-3:2003 has been approved by CEN as EN ISO 5167-3:2003 without any
modifications.
NOTE Normative references to International Standards are listed in Annex ZA (normative).
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 2003 Measurement of fluid flow by means of EN ISO 5167-1 2003
pressure differential devices inserted in
circular cross-section conduits running
full - Part 1: General principles and
requirements
INTERNATIONAL ISO
STANDARD 5167-3
First edition
2003-03-01
Measurement of fluid flow by means of
pressure differential devices inserted in
circular-cross section conduits running
full —
Part 3:
Nozzles and Venturi nozzles
Mesure de débit des fluides au moyen d'appareils déprimogènes
insérés dans des conduites en charge de section circulaire —
Partie 3: Tuyères et Venturi-tuyères

Reference number
ISO 5167-3:2003(E)
©
ISO 2003
ISO 5167-3:2003(E)
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ii © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 2
3 Terms and definitions. 2
4 Principles of the method of measurement and computation. 2
5 Nozzles and Venturi nozzles. 3
5.1 ISA 1932 nozzle . 3
5.2 Long radius nozzles. 9
5.3 Venturi nozzles. 13
6 Installation requirements . 18
6.1 General. 18
6.2 Minimum upstream and downstream straight lengths for installation between various
fittings and the primary device. 18
6.3 Flow conditioners . 23
6.4 Circularity and cylindricality of the pipe. 23
6.5 Location of primary device and carrier rings. 24
6.6 Method of fixing and gaskets . 25
Annex A (informative) Tables of discharge coefficients and expansibility [expansion] factors. 26
Bibliography . 30

ISO 5167-3:2003(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 5167-3, together with the second edition of ISO 5167-1 and the first editions of
ISO 5167-2 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

ISO 5167-3:2003(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.
INTERNATIONAL STANDARD ISO 5167-3:2003(E)

Measurement of fluid flow by means of pressure differential
devices inserted in circular-cross section conduits running
full —
Part 3:
Nozzles and Venturi nozzles
1 Scope
This part of ISO 5167 specifies the geometry and method of use (installation and operating conditions) of
nozzles and Venturi nozzles 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 nozzles and Venturi nozzles in which the flow remains subsonic
throughout the measuring section and where the fluid can be considered as single-phase. In addition, each of
the devices can only be used within specified limits of pipe size and Reynolds number. It is not applicable to
the measurement of pulsating flow. It does not cover the use of nozzles and Venturi nozzles in pipe sizes less
than 50 mm or more than 630 mm, or where the pipe Reynolds numbers are below 10 000.
This part of ISO 5167 deals with
a) two types of standard nozzles:
5)
1) the ISA 1932 nozzle;
6)
2) the long radius nozzle ;
b) the Venturi nozzle.
The two types of standard nozzle are fundamentally different and are described separately in this part of
ISO 5167. The Venturi nozzle has the same upstream face as the ISA 1932 nozzle, but has a divergent
section and, therefore, a different location for the downstream pressure tappings, and is described separately.
This design has a lower pressure loss than a similar nozzle. For both of these nozzles and for the Venturi
nozzle 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.
____________________________
5) ISA is the abbreviation for the International Federation of the National Standardizing Associations, which was
superseded by ISO in 1946.
6) The long radius nozzle differs from the ISA 1932 nozzle in shape and in the position of the pressure tappings.
ISO 5167-3:2003(E)
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 and definitions
For the purposes of this document, the terms and definitions given in ISO 4006 and ISO 5167-1 apply.
4 Principles of the method of measurement and computation
The principle of the method of measurement is based on the installation of a nozzle or a Venturi nozzle into a
pipeline in which a fluid is running full. The installation of the primary device causes a static pressure
difference between the upstream side and the throat. The flowrate can be determined from the measured
value of this pressure difference and from the knowledge of the characteristics of the flowing fluid as well as
the circumstances under which the device is being used. It is assumed that the device is geometrically similar
to one on which calibration has been carried out and that the conditions of use are the same, i.e. that it is in
accordance with this part of ISO 5167.
The mass flowrate can be determined by Equation (1):
C π
qd=∆ερ2p (1)
m 1
1− β
The uncertainty limits can be calculated using the procedure given in Clause 8 of ISO 5167-1:2003.
Similarly, the value of the volume flowrate can be calculated since
q
m
q = (2)
V
ρ
where ρ is the fluid density at the temperature and pressure for which the volume is stated.
Computation of the flowrate, which is a purely arithmetic process, is performed by replacing the different items
on the right-hand side of Equation (1) by their numerical values. Tables A.1 to A.4 are given for convenience.
Tables A.1 to A.3 give the values of C as a function of β. Table A.4 gives expansibility (expansion) factors ε.
They are not intended for precise interpolation. Extrapolation is not permitted.
The coefficient of discharge C may be dependent on Re , which is itself dependent on q and has to be

D
m
obtained by iteration. (See ISO 5167-1 for guidance regarding the choice of the iteration procedure and initial
estimates.)
The diameters d and D mentioned in Equation (1) 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 primary device and the pipe due to the values of the temperature and pressure of the fluid during the
measurement.
2 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
It is necessary to know the density and the viscosity of the fluid at 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 Nozzles and Venturi nozzles
5.1 ISA 1932 nozzle
5.1.1 General shape
The part of the nozzle inside the pipe is circular. The nozzle consists of a convergent section, of rounded
profile, and a cylindrical throat.
Figure 1 shows the cross-section of an ISA 1932 nozzle at a plane passing through the centreline of the throat.
The letters in the following text refer to those shown on Figure 1.
5.1.2 Nozzle profile
5.1.2.1 The profile of the nozzle may be characterized by distinguishing:
 a flat inlet part A, perpendicular to the centreline;
 a convergent section defined by two arcs of circumference B and C;
 a cylindrical throat E; and
 a recess F which is optional (it is required only if damage to the edge G is feared).
5.1.2.2 The flat inlet part A is limited by a circumference centred on the axis of revolution, with a diameter
of 1,5d, and by the inside circumference of the pipe, of diameter D.
When d = 2D/3, the radial width of this flat part is zero.
When d is greater than 2D/3, the upstream face of the nozzle does not include a flat inlet part within the pipe.
In this case, the nozzle is manufactured as if D is greater than 1,5d, and the inlet flat part is then faced off so
that the largest diameter of the convergent profile is just equal to D [see 5.1.2.7 and Figure 1 b)].
5.1.2.3 The arc of circumference B is tangential to the flat inlet part A when d < 2D/3 while its radius R is
equal to 0,2d ± 0,02d for β < 0,5 and to 0,2d ± 0,006d for β W 0,5. Its centre is at 0,2d from the inlet plane and
at 0,75d from the axial centreline.
5.1.2.4 The arc of circumference C is tangential to the arc of circumference B and to the throat E. Its
radius R is equal to d/3 ± 0,033d for β < 0,5 and to d/3 ± 0,01d for β W 0,5. Its centre is at d/2 + d/3 = 5d/6 from
the axial centreline and at

12 + 39
ad== 0,304 1d

n


from the flat inlet part A.
ISO 5167-3:2003(E)
Key
1 portion to be cut off
a
See 5.1.2.7.
b
Direction of flow.
Figure 1 — ISA 1932 nozzle
5.1.2.5 The throat E has a diameter d and a length b = 0,3d.
n
The value d of the diameter of the throat shall be taken as the mean of the measurements of at least four
diameters distributed in axial planes and at approximately equal angles to each other.
The throat shall be cylindrical. No diameter of any cross-section shall differ by more than 0,05 % from the
value of the mean diameter. This requirement is considered to be satisfied when the deviations in the length of
any of the measured diameters comply with the said requirement in respect of deviation from the mean.
4 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
5.1.2.6 The recess F has a diameter c equal to at least 1,06d and a length less than or equal to 0,03d.
n
The ratio of the height (c −d)/2 of the recess to its axial length shall not be greater than 1,2.
n
The outlet edge G shall be sharp.
5.1.2.7 The total length of the nozzle, excluding the recess F, as a function of β is equal to
0,604 1d for 0,3uuβ
and

0,75 0,25 2

0,404 1+− − 0,522 5 d for < βu 0,8 .

β 3
β

5.1.2.8 The profile of the convergent inlet shall be checked by means of a template.
Two diameters of the convergent inlet in the same plane perpendicular to the axial centreline shall not differ
from each other by more than 0,1 % of their mean value.
5.1.2.9 The surface of the upstream face and the throat shall be polished such that they have a
−4
roughness criterion Ra u 10 d.
5.1.3 Downstream face
5.1.3.1 The thickness H shall not exceed 0,1D.
5.1.3.2 Apart from the condition given in 5.1.3.1, the profile and the surface finish of the downstream face
are not specified (see 5.1.1).
5.1.4 Material and manufacture
The ISA 1932 nozzle may be manufactured from any material and in any way, provided that it remains in
accordance with the foregoing description during flow measurement.
5.1.5 Pressure tappings
5.1.5.1 Corner pressure tappings shall be used upstream of the nozzle.
The upstream pressure tappings may be either single tappings or annular slots. Both types of tappings may
be located either in the pipe or its flanges or in carrier rings as shown in Figure 1.
The spacing between the centrelines of individual upstream tappings and face A is equal to half the diameter
or to half the width of the tappings themselves, so that the tapping holes break through the wall flush with
face A. The centreline of individual upstream tappings shall meet the centreline of the primary device at an
angle of as near 90° as possible.
The diameter δ of a single upstream tapping and the width a of annular slots are specified below. The
minimum diameter is determined in practice by the need to prevent accidental blockage and to give
satisfactory dynamic performance.
For clean fluids and vapours:
 for β u 0,65: 0,005D u a or δ u 0,03D;
 for β > 0,65: 0,01D u a or δ u 0,02D.
ISO 5167-3:2003(E)
For any value of β:
 for clean fluids: 1 mm u a or δ u 10 mm;
 for vapours, in the case of annular chambers: 1 mm u a u 10 mm;
 for vapours and for liquefied gases, in the case of single tappings: 4 mm u δ u 10 mm.
The annular slots usually break through the pipe over the entire perimeter, with no break in continuity. If not,
each annular chamber shall connect with the inside of the pipe by at least four openings, the axes of which
are at equal angles to one another and the individual opening area of which is at least 12 mm .
The internal diameter b of the carrier rings shall be greater than or equal to the diameter D of the pipe, to
ensure that they do not protrude into the pipe, but shall be less than or equal to 1,04D. Moreover, the following
condition shall be met:
bD− c 0,1
××100u
DD
0,1+ 2,3β
The length c of the upstream ring (see Figure 1) shall not be greater than 0,5D.
The thickness f of the slot shall be greater than or equal to twice the width a of the annular slot. The area of
the cross-section of the annular chamber, gh, shall be greater than or equal to half the total area of the
opening connecting this chamber to the inside of the pipe.
All surfaces of the ring which are in contact with the measured fluid shall be clean and shall have a well-
machined finish.
The pressure tappings connecting the annular chambers to the secondary devices are pipe-wall tappings,
circular at the point of break-through and with a diameter j between 4 mm and 10 mm.
The upstream and downstream carrier rings need not necessarily be symmetrical in relation to each other, but
they shall both conform to the preceding requirements.
The diameter of the pipe shall be measured as specified in 6.4.2, the carrier ring being regarded as part of the
primary device. This also applies to the distance requirement given in 6.4.4 so that s shall be measured from
the upstream edge of the recess formed by the carrier ring.
5.1.5.2 The downstream pressure tappings may either be corner tappings as described in 5.1.5.1 or be
as described in the remainder of this section.
The distance between the centre of the tapping and the upstream face of the nozzle shall be
 u 0,15D for β u 0,67
 u 0,20D for β > 0,67
When installing the pressure tappings, due account shall be taken of the thickness of the gaskets and/or
sealing material.
The centreline of the tapping shall meet the pipe centreline at an angle as near to 90° as possible but in every
case within 3° of the perpendicular. At the point of break-through, the hole shall be circular. The edges shall
be flush with the internal surface of the pipe wall and as sharp as possible. To ensure the elimination of all
burrs or wire edges at the inner edge, rounding is permitted but shall be kept as small as possible and, where
it can be measured, its radius shall be less than one-tenth of the pressure-tapping diameter. No irregularity
shall appear inside the connecting hole, on the edges of the hole drilled in the pipe wall or on the pipe wall
close to the pressure tapping. Conformity of the pressure tappings with the requirements of this paragraph
may be judged by visual inspection.
6 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
The diameter of pressure tappings shall be less than 0,13D and less than 13 mm.
No restriction is placed on the minimum diameter, which is determined in practice by the need to prevent
accidental blockage and to give satisfactory dynamic performance. The upstream and downstream tappings
shall have the same diameter.
The pressure tappings shall be circular and cylindrical over a length of at least 2,5 times the internal diameter
of the tapping, measured from the inner wall of the pipeline.
The centrelines of the pressure tappings may be located in any axial plane of the pipeline.
The axis of the upstream tapping and that of the downstream tapping may be located in different axial planes.
5.1.6 Coefficients of ISA 1932 nozzles
5.1.6.1 Limits of use
This type of nozzle shall only be used in accordance with this part of ISO 5167 when
 50 mm u D u 500 mm
 0,3 u β u 0,8
and when Re is within the following limits:
D
4 7
 for 0,30 u β < 0,44 7 × 10 u Re u 10
D
4 7
 for 0,44 u β u 0,80 2 × 10 u Re u 10
D
In addition, the relative roughness of the pipe shall conform to the values given in Table 1.
Table 1 — Upper limits of relative roughness of the upstream pipe for ISA 1932 nozzles
β u 0,35 0,36 0,38 0,40 0,42 0,44 0,46 0,48 0,50 0,60 0,70 0,77 0,80
10 Ra/D 8,0 5,9 4,3 3,4 2,8 2,4 2,1 1,9 1,8 1,4 1,3 1,2 1,2
NOTE Most of the data on which this table is based were probably collected in the range Re u 10 ; at higher Reynolds numbers
D
more stringent limits on pipe roughness are probably required.
Most of the experiments on which the values of the discharge coefficient C given in this part of ISO 5167 are
−4
based were carried out in pipes with a relative roughness Ra/D u 1,2 × 10 . Pipes with higher relative
roughness may be used if the roughness for a distance of at least 10D upstream of the nozzle is within the
limits given in Table 1. Information as to how to determine Ra is given in ISO 5167-1.
5.1.6.2 Discharge coefficient, C
The discharge coefficient, C, is given by Equation (3):
1,15

4,1 2 4,15
C=−0,990 0 0,226 2ββ− 0,00175− 0,003 3β  (3)
()

Re
D

Values of C as a function of β and Re are given for convenience in Table A.1. These values are not intended
D
for precise interpolation. Extrapolation is not permitted.
ISO 5167-3:2003(E)
5.1.6.3 Expansibility [expansion] factor,  ε
The expansibility [expansion] factor, ε, is calculated by means of Equation (4):
24κκ( −1)κ
  
κτ 11−−β τ
ε =     (4)
42 κ
  
κτ−−11
1−βτ
  
Equation (4) is applicable only for values of β, D and Re as specified in 5.1.6.1. Test results for determination
D
of ε are only known for air, steam and natural gas. However, there is no known objection to using the same
formula for other gases and vapours for which the isentropic exponent is known.
However, Equation (4) is applicable only if p /p W 0,75.
2 1
Values of the expansibility [expansion] factor for a range of isentropic exponents, pressure ratios and diameter
ratios are given for convenience in Table A.4. These values are not intended for precise interpolation.
Extrapolation is not permitted.
5.1.7 Uncertainties
5.1.7.1 Uncertainty of discharge coefficient C
When β, D, Re and Ra/D are assumed to be known without error, the relative uncertainty of the value of C is
D
equal to
 0,8 % for β u 0,6;
 (2β − 0,4) % for β > 0,6.
5.1.7.2 Uncertainty of expansibility [expansion] factor ε
The relative uncertainty of ε is equal to
∆p
2 %
p
5.1.8 Pressure loss, ∆ϖ
The pressure loss, ∆ϖ, for the ISA 1932 nozzle is approximately related to the differential pressure ∆p by
Equation (5)
42 2
1(−−ββ1CC)−
∆=ϖ ∆p (5)
42 2
1(−−ββ1)CC+
This pressure loss is the difference in static pressure between the pressure measured at the wall on the
upstream side of the primary device at a section where the influence of the approach impact pressure
adjacent to the device is still negligible (approximately D upstream of the primary device) and that measured
on the downstream side of the primary device where the static pressure recovery by expansion of the jet may
be considered as just completed (approximately 6D downstream of the primary device).
The pressure loss coefficient, K, for the ISA 1932 nozzle is
42
1(−−β1)C

K=−1 (6)

Cβ

8 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
where K is defined by Equation (7):
∆ϖ
(7)
K =
ρ U
5.2 Long radius nozzles
5.2.1 General
There are two types of long radius nozzle, which are called
 high-ratio nozzles (0,25 u β u 0,8), and
 low-ratio nozzles (0,20 u β u 0,5).
For β values between 0,25 and 0,5 either design may be used.
Figure 2 illustrates the geometric shapes of long radius nozzles, showing cross-sections passing through the
throat centrelines.
The reference letters used in the text refer to those shown on Figure 2.
Both types of nozzles consist of a convergent inlet, whose shape is a quarter ellipse, and a cylindrical throat.
That part of the nozzle which is inside the pipe shall be circular, with the possible exception of the holes of the
pressure tappings.
5.2.2 Profile of high-ratio nozzle
5.2.2.1 The inner face can be characterized by
 a convergent section A,
 a cylindrical throat B, and
 a plain end C.
5.2.2.2 The convergent section A has the shape of a quarter ellipse.
The centre of the ellipse is at a distance D/2 from the axial centreline. The major centreline of the ellipse is
parallel to the axial centreline. The value of half the major axis is D/2. The value of half the minor axis is
(D−d)/2.
The profile of the convergent section shall be checked by means of a template. Two diameters of the
convergent section in the same plane perpendicular to the centreline shall not differ from each other by more
than 0,1 % of their mean value.
5.2.2.3 The throat B has a diameter d and a length 0,6d.
The value d of the diameter of the throat shall be taken as the mean of the measurements of at least four
diameters distributed in axial planes and at approximately equal angles to each other.
The throat shall be cylindrical. Any diameter of any cross-section shall not differ by more than 0,05 % from the
value of the mean diameter. Measurement at a sufficient number of cross-sections shall be made to determine
that under no circumstances is the throat divergent in the direction of flow; within the stated uncertainty limits it
may be slightly convergent. The section nearest the outlet is particularly important in this respect. This
requirement is considered to be satisfied when the deviations in the length of any of the measured diameters
comply with the said requirement in respect of its deviation from the mean.
ISO 5167-3:2003(E)
a)  High ratio 0,25 u β u 0,8

b)  Low ratio 0,2 u β u 0,5
a
Direction of flow.
Figure 2 — Long radius nozzles
10 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
5.2.2.4 The distance between the pipe wall and the outside face of the throat shall be greater than or
equal to 3 mm.
5.2.2.5 The thickness H shall be greater than or equal to 3 mm and less than or equal to 0,15D. The
thickness F of the throat shall be greater than or equal to 3 mm, unless D u 65 mm, in which case F shall be
greater than or equal to 2 mm. The thickness shall be sufficient to prevent distortion due to machining stresses.
−4
5.2.2.6 The surface of the inner face shall have a roughness criterion Ra u 10 d.
5.2.2.7 The shape of the downstream (outside) face is not specified but shall comply with 5.2.2.4 and
5.2.2.5 and the last sentence of 5.2.1.
5.2.3 Profile of low-ratio nozzle
5.2.3.1 The requirements given in 5.2.2 for the high-ratio nozzle shall apply also to the low-ratio nozzle
with the exception of the shape of the ellipse itself which is given in 5.2.3.2.
5.2.3.2 The convergent inlet A has the shape of a quarter ellipse. The centre of the ellipse is at a distance
d/2 + 2d/3 = 7d/6 from the axial centreline. The major axis of the ellipse is parallel to the axial centreline. The
value of half the major axis is d. The value of half the minor axis is 2d/3.
5.2.4 Material and manufacture
The long radius nozzle may be manufactured from any material and in any way, provided that it remains in
accordance with the foregoing description during flow measurement.
5.2.5 Pressure tappings
+0,2D
5.2.5.1 The centreline of the upstream tapping shall be at 1D from the inlet face of the nozzle.
−0,1D
The centreline of the downstream tapping shall be at 0,50D ± 0,01D from the inlet face of the nozzle except in
the case of a low ratio nozzle with β < 0,318 8 for which the centreline of the downstream tapping shall be at
+0
1,6d from the inlet face of the nozzle.
−0,02D
When installing the pressure tappings, due account shall be taken of the thickness of the gaskets and/or
sealing material.
5.2.5.2 The centreline of the tapping shall meet the pipe centreline at an angle as near to 90° as possible
but in every case within 3° of the perpendicular. At the point of break-through the hole shall be circular. The
edges shall be flush with the internal surface of the pipe wall and as sharp as possible. To ensure the
elimination of all burrs or wire edges at the inner edge, rounding is permitted but shall be kept to a minimum
and, where it can be measured, its radius shall be less than one-tenth of the pressure-tapping diameter. No
irregularity shall appear inside the connecting hole, on the edges of the hole drilled in the pipe wall or on the
pipe wall close to the pressure tapping. Conformity of the pressure tappings with the requirements of this
paragraph may be judged by visual inspection.
The diameter of pressure tappings shall be less than 0,13D and less than 13 mm.
No restriction is placed on the minimum diameter, which is determined in practice by the need to prevent
accidental blockage and to give satisfactory dynamic performance. The upstream and downstream tappings
shall have the same diameter.
The pressure tappings shall be circular and cylindrical over a length of at least 2,5 times the internal diameter
of the tapping, measured from the inner wall of the pipeline.
The centrelines of the pressure tappings may be located in any axial plane of the pipeline.
The axis of the upstream tapping and that of the downstream tapping may be located in different axial planes.
ISO 5167-3:2003(E)
5.2.6 Coefficients of long radius nozzles
5.2.6.1 Limits of use
The long radius nozzles shall only be used in accordance with this part of ISO 5167 when
 50 mm u D u 630 mm
 0,2 u β u 0,8
4 7
 10 u Re u 10
D
−4
 Ra/D u 3,2 × 10 in the upstream pipe work.
Pipes with higher relative roughness may be used if the roughness for a distance of at least 10D upstream of
the nozzle is within the limit given above. Information as to how to determine Ra is given in ISO 5167-1.
NOTE Most of the data on which this pipe roughness limit is based, were probably collected in the range Re u 10 ;
d
at higher Reynolds numbers more stringent limits on pipe roughness are probably required.
5.2.6.2 Discharge coefficient, C
The discharge coefficients, C, are the same for both types of long radius nozzle when the tappings are in
accordance with 5.2.5.
The discharge coefficient, C, is given by Equation (8), when referring to the upstream pipe Reynolds number
Re :
D
10 β
C=−0,996 5 0,006 53 (8)
Re
D
When referring to the Reynolds number at the throat Re , Equation (8) becomes
d
C=−0,996 5 0,006 53 (9)
Re
d
and, in this case, C is independent of the diameter ratio β.
Values of C as a function of β and Re are given for convenience in Table A.2. These values are not intended
D
for precise interpolation. Extrapolation is not permitted.
5.2.6.3 Expansibility [expansion] factor, ε
The indications given in 5.1.6.3 apply also to the expansibility [expansion] factor for long radius nozzles, but
within the limits of use specified in 5.2.6.1.
5.2.7 Uncertainties
5.2.7.1 Uncertainty of discharge coefficient C
When β and Re are assumed to be known without error, the relative uncertainty of the value of C is 2,0 % for
d
all values of β between 0,2 and 0,8.
12 © ISO 2003 — All rights reserved

ISO 5167-3:2003(E)
5.2.7.2 Uncertainty of expansibility [expansion] factor ε
The relative uncertainty of ε is equal to
∆p
2 % (10)
p
5.2.8 Pressure loss, ∆ϖ
Subclause 5.1.8 applies equally to the pressure loss of long radius nozzles.
5.3 Venturi nozzles
5.3.1 General shape
5.3.1.1 The profile of the Venturi nozzle (see Figure 3) is axisymmetric. It consists of a convergent
section, with a rounded profile, a cylindrical throat and a divergent section.
5.3.1.2 The upstream face is identical with that of an ISA 1932 nozzle (see Figure 1).
5.3.1.3 The flat inlet part A is limited by a circumference centred on the axis of revolution, with a diameter
of 1,5d, and by the inside circumference of the pipe, of diameter D.
When d = 2D/3, the radial width of this flat part is zero.
When d is greater than 2D/3, the upstream face of the nozzle does not include a flat inlet part within the pipe.
In this case, the nozzle is manufactured as if D is greater than 1,5d and the inlet flat part is then faced off so
that the largest diameter of the convergent profile is just equal to D.
5.3.1.4 The arc of circumference B is tangential to the flat inlet part A when d < 2D/3 while its radius R is
equal to 0,2d ± 0,02d for β < 0,5 and to 0,2d ± 0,006d for β W 0,5. Its centre is at 0,2d from the inlet plane and
at 0,75d from the axial centreline.
5.3.1.5 The arc of circumference C is tangential to the arc of circumference B and to the throat E. Its
radius R is equal to d/3 ± 0,033d for β < 0,5 and to d/3 ± 0,01d for β W 0,5. Its centre is at d/2 + d/3 = 5d/6 from
the axial centreline and at

12 + 39
ad== 0,304 1d

n


from the flat inlet part A.
5.3.1.6 The throat (see Figure 3) consists of a part E of length 0,3d and a part F of a length 0,4d to 0,45d.
The value d of the diameter o
...