ISO 16399:2014

INTERNATIONAL ISO
STANDARD 16399
First edition
2014-05-01
Meters for irrigation water
Compteurs pour l’eau d’irrigation
Reference number
©
ISO 2014
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Metrological characteristics . 5
4.1 Maximum permissible error (MPE) . 5
4.2 Metrological characteristics . 5
5 Technical characteristics . 6
5.1 General specifications . 6
5.2 Rated operating conditions . 7
5.3 Materials . 7
5.4 Indicating device . 7
5.5 Reverse flow . 8
5.6 Sealing and security . 8
5.7 Other devices . 9
6 Metrological requirements . 9
6.1 Indicating error . 9
6.2 Internal pressure . 9
6.3 Flow profile sensitivity classes . 9
6.4 Pressure loss .10
7 Performance tests .11
7.1 General conditions for the tests .11
7.2 Static pressure test .12
7.3 Determination of errors .12
7.4 Pressure loss test .14
7.5 Flow disturbance tests .14
7.6 Reverse flow test .17
7.7 Endurance tests .18
8 Tests related to the influence quantities and perturbations .24
9 Marking .24
Annex A (informative) Pulse input solutions .26
Annex B (normative) Flow disturbers .33
Bibliography .47
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 23, Tractors and machinery for agriculture and
forestry, Subcommittee SC 18, Irrigation and drainage equipment and systems.
iv © ISO 2014 – All rights reserved

INTERNATIONAL STANDARD ISO 16399:2014(E)
Meters for irrigation water
1 Scope
This International Standard applies to water meters intended for irrigation use (herein after referred to
as water meters), regardless of the water quality used for this purpose, and specifies the requirements
and certification procedures for water meters, irrespective of the design technologies used to meter the
actual volume of cold water or heated water flowing through a fully charged closed conduit. These water
meters incorporate devices which indicate the integrated volume.
This International Standard also applies to water meters based on electrical or electronic principles
and to water meters based on mechanical principles, incorporating electronic devices used to meter
the actual volume flow of cold water. It provides metrological requirements for electronic ancillary
devices when they are subject to metrological control. As a rule, the ancillary devices are optional.
However national or international regulations make some ancillary devices mandatory in relation to
the utilization of the water meter.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 4064-1:2005, Measurement of water flow in fully charged closed conduits — Meters for cold potable
water and hot water — Part 1: Specifications
ISO 4064-2:2005, Measurement of water flow in fully charged closed conduits — Meters for cold potable
water and hot water — Part 2: Installation requirements
ISO 9644, Agricultural irrigation equipment — Pressure losses in irrigation valves — Test method
ISO 286-2, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes —
Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
ISO 228-1, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions,
tolerances and designation
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
water meter
instrument intended to measure continuously, store, and display the volume of water passing through
the measurement transducer at metering conditions
Note 1 to entry: A water meter includes at least a measurement transducer, a calculator (including adjustment or
correction devices, if present), and an indicating device. These three devices may be in different housings.
[SOURCE: OIML R49-1:2006, 2.1.1, modified — The second note is not included here.]
3.2
indicating device
part of the meter that provides an indication corresponding to the volume of water passing through the
meter
3.3
actual volume
V
a
total volume of water passing through the meter
Note 1 to entry: The actual volume is calculated from a reference volume as determined by a suitable measurement
standard taking into account differences in metering conditions, as appropriate.
[SOURCE: OIML R49-1:2006, 2.2.1, modified — The phrases “disregarding the time taken” and “This is
the measurand” have been removed from the definition.]
3.4
indicated volume
V
i
volume of water indicated by the meter, corresponding to the actual volume
[SOURCE: OIML R49-1:2006]
3.5
flow rate
Q
volume of water flowing through a device per unit time
3.6
minimum flow rate
Q
lowest flow rate at which the meter is required to operate within the maximum permissible error
3.7
transitional flow rate
Q
flow rate between the permanent flow rate ≥ 100 ≥ 10 and the minimum flow rate ≥5 that divides the
flow rate range into two zones, the “upper zone” and the “lower zone”, each characterized by its own
maximum permissible error
3.8
permanent flow rate
Q
highest flow rate under normal service conditions at which the meter is required to operate in a
satisfactory manner within the maximum permissible error
3.9
overload flow rate
Q
highest flow rate at which the water meter is designed to operate for a short period of time within its
maximum permissible error, whilst maintaining its metrological performance when it is subsequently
operated under normal service conditions
3.10
test flow rate
mean flow rate during a test, calculated from the indications of a calibrated reference device
2 © ISO 2014 – All rights reserved

3.11
error
measured quantity value minus a reference quantity value
VV−
ia
×100(%)
V
a
3.12
maximum permissible error
MPE
extreme value of error permitted by this International Standard
3.13
working pressure
P
w
average water pressure in the pipe measured upstream of the meter
3.14
durability
ability of a meter to maintain its performance characteristics over a period of use
3.15
metering conditions
conditions of the water, the volume of which is to be measured, at the point of measurement
EXAMPLE Water temperature, water pressure.
3.16
maximum admissible pressure
MAP
maximum internal pressure that the meter can withstand permanently, within its rated operating
conditions, without deterioration of its metrological performance
Note 1 to entry: MAP is equivalent to Nominal Pressure (PN).
3.17
working temperature
T
w
average water temperature in the pipe, measured upstream and downstream of a water meter
[SOURCE: OIML R49-1:2006]
3.18
minimum and maximum admissible temperature
mAT, MAT
minimum and maximum water temperatures that a meter can withstand permanently, within its rated
operating conditions, without deterioration of its metrological performance
Note 1 to entry: mAT and MAT are respectively the lower and upper of the rated operating conditions (ROC).
[SOURCE: OIML R49-1:2006, 2.3.7]
3.19
pressure loss
difference in pressure due to water flow between two specified points in a system or in part of a system
3.20
limiting condition
extreme condition that a meter is required to withstand without damage, and without degradation of its
specified metrological properties, when it is subsequently operated under its rated operating conditions
3.21
nominal diameter
DN
numerical designation used to indicate the size of a gated pipe approximately equal to the outside
diameter of the pipe
3.22
influence variable
quantity that, in a direct measurement, does not affect the quantity that is actually measured, but affects
the relation between the indication and the measurement result
3.23
influence factor
influence variable having a value within the rated operating conditions specified for a water meter
3.24
rated operating condition
ROC
operating condition that must be fulfilled during measurement in order that a meter performs as
designed
Note 1 to entry: The rated operating conditions specify intervals for the flow rate and for the influence parameters
for which the errors are required to be within the maximum permissible errors.
[SOURCE: ISO/IEC Guide 99:2007, 4.9, modified — In the definition, the phrase “measuring instrument
or measuring system” has been changed to “meter”. The note is different.]
3.25
reed contact unit
assembly containing contact blades, some or all of magnetic material, hermetically sealed in an envelope
and controlled by means of externally generated magnetic field (e.g. a pulse generator)
3.26
measuring state
state when the switch is closed
3.27
bounce
momentary re-opening of a contact after initial closing, or a momentary closing after initial opening
3.28
bounce time
interval of time between the instant of the first closing (or opening) and the instant of the final closing
(or opening) of the reed contact unit
3.29
operate position time
interval of time between the instant the reed contact unit is in the operate position and the instant of the
removal of the applied magnetic field to the contact
Note 1 to entry: It includes the closing bounce time in a normally open contact or the opening bounce time in a
normally closed contact.
4 © ISO 2014 – All rights reserved

4 Metrological characteristics
4.1 Maximum permissible error (MPE)
4.1.1 Formulation
The error is expressed as a percentage, and is equal to:
VV−
()
ia
ε = ×100 (%)
V
a
(1)
where
V is the indicated volume;
i
V is the actual volume.
a
4.1.2 Limits
The maximum permissible error, positive or negative, on volumes delivered at flow rates (Q) between
the minimum flow rate (Q ) (included) and the transitional flow rate (Q ) (excluded) is 5 %.
1 2
The maximum permissible error, positive or negative, on volumes delivered at flow rates between the
transitional flow rate (Q ) (included) and the overload flow rate (Q ) (included) is 2 %.
2 4
— Q ≤ Q < Q , MPE ≤ 5 %
1 2
— Q ≤ Q ≤ Q , MPE ≤ 2 %
2 4
If all the errors within the measuring range of the water meter have the same sign, at least one of the
errors shall be less than one half of the maximum permissible error.
When any accessory part is sold with the water meter, as for instance a control valve, the error shall be
calculated for any position of the accessory, not altering the metrological characteristics of the water
meter.
The maximum permissible error declared by the manufacturer is intended for any recommended
installation configuration.
4.2 Metrological characteristics
4.2.1 Permanent flow rate (Q )
The value of Q , in (m /h), shall be chosen from the following list:
1,0 1,6 2,5 4,0 6,3
10 16 25 40 63
100 160 250 400 630
1 000 1 600 2 500 4 000 6 300
This list may be extended to higher or lower values in the series.
4.2.2 Measuring range
The measuring range for the flow rate is defined by the ratio Q /Q . The values shall be chosen from the
3 1
following list:
10 12,5 16 20 25 31,5 40 50 63 80
100 125 160 200 250 315 400 500 630 800
This list may be extended to higher values in the series.
4.2.3 Relationship between permanent flow rate (Q) and overload flow rate (Q )
3 4
The overload flow rate is defined by:
Q /Q = 1,25
4 3
(2)
4.2.4 Relationship between transitional flow rate (Q) and minimum flow rate (Q )
2 1
The transitional flow rate is defined by:
Q /Q = 1,6
2 1
(3)
e.g. Q = 100; Q /Q = 10 (R10); Q /Q = 1,6; Q /Q = 1,25
3 3 1 2 1 4 3
where
Q = 100 m /h;
Q = 10 m /h;
Q = 16 m /h;
Q = 125 m /h.
5 Technical characteristics
5.1 General specifications
The water meters shall be made so that they
a) guarantee their design useful lifetime and exclude fraud possibility, and
b) fulfil the requirements of this International Standard, under rated operating conditions.
Additional specifications are the following.
— A water meter measures continuously, records and displays the integrated volume of water passing
through the measurement transducer.
NOTE A water meter includes at least a measurement transducer, a calculator, and an indicating device.
— The manufacturer shall specify in the instruction manual the conditions in which the meter can
operate in the event of reversal of the flow direction.
6 © ISO 2014 – All rights reserved

— Other ancillary functions of output and input of information (remote reading, prepayment, etc.) may
be included provided they do not affect the performance of the meters as defined in this International
Standard.
— The meter will preferably be designed in such a way as to present as little disturbance as possible to
the water flow and any solid materials it may transport.
— The meter shall be designed such that its operation cannot be affected by a magnetic field as defined
in ISO 4064-1:2005, 7.2.7.
5.2 Rated operating conditions
The rated operating conditions for a water meter shall be as follows:
a) ambient temperature range (T ): 0,1 °C ≤ T < 50 °C;
amb amb
b) pressure (P): P < MAP (maximum admissible pressure);
c) water temperature range [working temperature (T )]: 0,1 °C ≤ T < 30 °C;
w w
d) flow rate range (Q): Q (minimum flow rate) < Q ≤ Q (permanent flow rate);
1 3
e) power supply voltage (mains a.c.): nominal voltage (U ) ± 5 %;
nom
f) power supply frequency: nominal frequency ( f ) ± 2 %;
nom
g) power supply voltage (battery): a voltage, U, in the range; U ≤ U ≤ U .
bmin bmax
5.3 Materials
The water meter shall be fabricated with materials with a resistance and stability suitable for its use.
The meter shall be fabricated using materials which are resistant to internal and external corrosion,
and, if required, will be protected by the application of an appropriate surface treatment.
Water temperature variations within the working temperature range will not adversely affect the
materials used.
5.4 Indicating device
5.4.1 Function
The indicating device shall always guarantee easy reading of volumes without ambiguity.
5.4.2 Unit of measurement
The indicated volume of water shall be expressed in cubic metres. The symbols m shall appear on the
dial or immediately adjacent to the numbered display.
5.4.3 Indicating range
This requirement is set in Table 1:
Table 1 — Indicating range
Indicating range
Q
(minimum values)
m /h
m
Q ≤ 6,3 9 999
6,3 < Q ≤ 63 99 999
63 < Q ≤ 630 999 999
630 < Q ≤ 6 300 9 999 999
5.4.4 Colour coding for indicating devices
The colour black shall be used to indicate the cubic metre and its multiples.
The colour red shall be used to indicate sub-multiples of a cubic metre.
These colours shall be applied to the pointers, indices, numbers, wheels, discs, dials, or aperture frames.
It is allowed to use other manner of indicating the volume for electronic water meters, provided the
volume is expressed in cubic metres, and there is no ambiguity in distinguishing between the primary
indication and alternative displays, e.g. sub-multiples for verification and testing.
5.5 Reverse flow
For meters designed to measure reverse flow, the permanent flow rate and the measuring range may be
different in each direction.
The manufacturer shall specify whether the meter is designed to measure reverse flow. If it is, the reverse
flow volume shall either be subtracted from the indicated volume, or it shall be separately recorded. The
maximum permissible error of 4.1.2 shall be met for forward and reverse flow.
Water meters not designed to measure reverse flow shall either prevent it or they shall be capable of
withstanding an accidental reverse flow without any deterioration or change in their metrological
properties for forward flow, and without modification of the cumulated volume.
5.6 Sealing and security
5.6.1 Meter security and protection against manipulations
Considerations of water meter security and protection against fraud concern only the water meter
including primary indications.
5.6.2 Mechanical protection devices
Water meters shall incorporate protective devices, such as seals, that prevent the water meter from
being disassembled or altered without permanently damaging the seal or the protective device.
5.6.3 Electronic sealing devices
When access to modify parameters that influence the determination of the results of measurements
is not protected by mechanical sealing devices, the protection shall fulfil the provisions described in
ISO 4064-1:2005, 5.8.3.
8 © ISO 2014 – All rights reserved

5.7 Other devices
Water meters can incorporate other devices as, for example, reed switches. In such case, the manufacturer
shall ensure that the devices don’t affect the metrological characteristics of the water meter and that
such devices have full compatibility with the water meter.
For example, in order to ensure full compatibility between a reed contact unit and a water meter, the
manufacturer can carry out the tests described in Annex A.
6 Metrological requirements
6.1 Indicating error
The water meters shall be designed so that their indicating errors do not exceed the MPE defined in
4.1.2, under rated operating conditions.
6.2 Internal pressure
The water meters shall withstand the internal pressure they are designed to, while in service, without any
significant influence on the performance characteristics, leaks, exudation, or permanent deformation.
This pressure value is named maximum admissible pressure.
The water meters are classified in function of the MAP declared by the manufacturer, as shown in Table 2:
Table 2 — Water pressure classes
Maximum admissible pressure
Class
(MPa) (bar)
Maximum admissible pressure 6 0,6 6
Maximum admissible pressure 10 1,0 10
Maximum admissible pressure 16 1,6 16
Maximum admissible pressure 25 2,5 25
Maximum Admissible pressure 40 4,0 40
6.3 Flow profile sensitivity classes
The water meter shall be able to withstand the influence of abnormal velocity profiles as defined in
the test procedures of 7.5. During the application of these flow disturbances, the error shall meet the
requirements of 4.1.2.
The water meter manufacturer shall specify the flow profile sensitivity class in accordance with Tables
3 and 4, based on the results of the relevant tests specified in 7.5.
Any flow conditioning section, including straightener and/or straight pipe lengths to be used, shall be
entirely defined by the manufacturer and is considered to be an auxiliary device linked to the type of
the water meter examined.
Table 3 — Sensitivity to the irregularity in the upstream velocity profiles classes (U)
Required straight
Class pipe lengths Straightener needed
(x DN)
U0 0 No
U3 3 No
U5 5 No
U10 10 No
U15 15 No
U0S 0 Yes
U3S 3 Yes
U5S 5 Yes
U10S 10 Yes
Table 4 — Sensitivity to the irregularity in the downstream velocity profiles classes (D)
Required straight
Class pipe lengths Straightener needed
(x DN)
D0 0 No
D3 3 No
D5 5 No
D0S 0 Yes
D3S 3 Yes
6.4 Pressure loss
The maximum pressure loss within rated operating conditions shall not exceed 63 kPa (0,63 bar),
between Q and Q . This includes pressure loss in any filter or strainer.
1 3
The pressure loss class is selected by the manufacturer from values taken from the following table:
Table 5 — Pressure-loss classes
Maximum pressure-loss
Class
(KPa) (bar)
ΔP 63 63 0,63
ΔP 40 40 0,40
ΔP 25 25 0,25
ΔP 16 16 0,16
ΔP 10 10 0,10
NOTE Maximum head loss can differ and be higher to the Q corresponding head loss.
10 © ISO 2014 – All rights reserved

7 Performance tests
7.1 General conditions for the tests
7.1.1 Water quality
Conduct water meter tests using water from the public clean water supply or water that meets the same
requirements.
Ensure that the water does not contain anything capable of damaging the water meter or adversely
affecting its operation. Avoid entrapped air.
7.1.2 Reference conditions
Table 6 — Reference conditions
Condition Admissible range
Water temperature range 4 °C to 35 °C
Working (water) pressure range 0,03 MPa to 1 MPa except DN > 500 that is 0,6 MPa
Ambient temperature range 4 °C to 35 °C
Ambient relative humidity range 35 % to 75 %
Ambient atmospheric pressure range 86 kPa to 106 kPa (0,86 bar to 1,06 bar)
7.1.3 Pressure
Ensure that the water pressure upstream of the water meter does not vary, during the test, by more than
10 %.
Ensure that the pressure at the entrance to the water meter does not exceed the maximum admissible
working pressure (P ) for the water meter.
w
During the test, the pressure at the water meter outlet shall be, at least, 0,03 MPa (0,3 bar).
The maximum uncertainty in the measurement of pressure (or pressure loss) shall be ± 5 % of the
measured value.
The estimated uncertainty shall be made according to Reference [4] in measurement with a coverage
factor, k = 2.
7.1.4 Flow rate
Ensure that the relative variation in the flow rate during each test (not including starting and stopping)
does not exceed:
— ±2, 5 % from Q to Q (not inclusive);
1 2
— ±5, 0 % from Q (inclusive) to Q .
2 4
The average flow rate value is the actual volume passed during the test divided by the time.
7.1.5 Temperature
Ensure that the temperature of the water during the test does not change by more than 5 °C.
Ensure that the maximum uncertainty in the measurement of temperature does not exceed ± 1 °C.
The estimated uncertainty shall be made according to Reference [4] in measurement with a coverage
factor, k = 2.
7.2 Static pressure test
7.2.1 Object of test
To verify that the water meter can withstand the specified hydraulic test pressure for the specific time,
without leakage or damage.
7.2.2 Preparation
a) Install the water meters in the test bench either individually or in groups.
b) Bleed the test bench pipe-work and the water meter of air.
c) Ensure that the test bench is free from leaks.
d) Ensure that the supply pressure is free from pressure pulsations.
7.2.3 Test procedure
a) Increase the hydraulic pressure to 1,6 times the maximum admissible pressure of the water meter
and hold it for 15 min.
b) Examine the water meters for physical damage, for external leaks and for leaks into the indicating
device.
c) Increase the hydraulic pressure to twice the maximum admissible pressure and hold it for 1 min.
Ensure that the flow rate is zero during the test.
d) Examine the water meters for physical damage, for external leaks and for leaks into the indicating
device.
Additional requirements:
e) Increase and decrease the pressure gradually without pressure surges.
7.2.4 Acceptance criteria
There shall be no leakage from the water meter or leakage into the indicating device, or physical damage,
resulting from any of the pressure tests.
7.3 Determination of errors
7.3.1 Object of test
The object of the test is to verify that the water meter complies with the requirements in 4.1.2 and to
determine the effects of the water meter orientation on the error.
7.3.2 Preparation
The method described here for determining the water meter errors is the so-called “collection” method,
in which the quantity of water passed through the water meter is collected in one or more collecting
vessels and that quantity is determined volumetrically or by weighing. Other methods may be used,
provided the requirements of uncertainty are met.
The error is checked by comparing the volume indications given by the water meter under reference
conditions against a calibrated reference device.
12 © ISO 2014 – All rights reserved

For the purpose of these tests, the water meter should be tested without its temporary supplementary
devices attached (if any).
7.3.2.1 Orientation of water meter(s)
Ensure that the position of the water meter (spatial orientation) is as indicated by the manufacturer and
that the meters are mounted in the test rig as appropriate.
a) If the water meters are marked “H”, mount the connecting pipework with the flow axis in the
horizontal plane during the test (indicating device positioned on top).
b) If the water meters are marked “V”, mount the connecting pipework with the flow axis in the vertical
plane during the test.
c) If the water meters are not marked either “H” or “V”:
1) mount at least one water meter from the sample with the flow axis vertical, with flow direction
from bottom to top;
2) mount at least one water meter from the sample with the flow axis vertical and flow direction
from top to bottom;
3) mount at least one water meter from the sample with the flow axis at an intermediate angle to
the vertical and horizontal (chosen at the discretion of the approving authority);
4) mount the remaining water meters from the sample with the flow axis horizontal;
5) where the water meters have an indicating device which is integral with the body of the
water meter, at least one of the horizontally mounted water meters shall be oriented with the
indicating device positioned at the side and the remaining water meters shall be oriented with
the indicating device positioned at the top.
d) Ensure that the tolerance on the position of the flow axis for all water meters, whether horizontal,
vertical or at an intermediate orientation is ±5°.
7.3.3 Test procedure
a) Determine the intrinsic errors of the water meter (in the measurement of the actual volume), for at
least the following six flow rates:
1) between Q and 1,1 Q ;
1 1
2) between Q and 1,1 Q ;
2 2
3) between 0,33 (Q + Q ) and 0,37 (Q + Q );
2 3 2 3
4) between 0,67 (Q + Q ) and 0,74 (Q + Q );
2 3 2 3
5) between 0,9 Q and Q ;
3 3
6) between 0,95 Q and Q .
4 4
b) Measure the errors at other flow rates if required, depending on the shape of the error curve;
c) Calculate the relative error for each flow rate.
7.3.4 Acceptance criteria
a) The errors observed for each of the six flow rates shall not exceed the maximum permissible errors.
If the error observed for one or more meters is greater than the maximum permissible error at one
flow rate only, repeat the test at that flow rate. The test shall be declared satisfactory if two out of
the three results lie within the maximum permissible error and the arithmetic mean of the results
for the three tests at that flow rate is less than or equal to the maximum permissible error.
b) If all the errors of the water meter have the same sign, at least one of these errors shall not exceed
one half of the maximum permissible error. In all cases, this requirement shall be applied equitably
with respect to the water supplier and the consumer.
c) The standard deviation for 7.3.3 a) 1), 2), and 5) shall not exceed one third of the maximum
permissible error given in 4.1.2.
d) When a test is conducted, the expanded uncertainty in the determination of the actual volume
passing through the water meter shall not exceed one-fifth of the applicable maximum permissible
error.
NOTE The uncertainty of the measured actual volume does not include a contribution from the water meter.
The estimated uncertainty shall be made according to ISO/IEC Guide 98-3 (GUM) in measurement with
a coverage factor, k = 2.
7.4 Pressure loss test
7.4.1 Object of test
The object of the test is to determine the maximum pressure loss through the water meter at any flow
rate between Q and Q and verify that the water meter complies with the requirements in 6.4.
1 3
To determine the maximum pressure loss through the water meter at any flow rate between Q and
Q . To verify the maximum pressure loss is less than 0,063 MPa (0,63 bar). The pressure loss is defined
as the pressure lost by the flowing fluid passing through the water meter under test, the water meter
consisting of the meter and connections but excluding the pipework making up the test section. The test
is required for forward flow and where appropriate for reverse flow.
7.4.2 Preparation
The installations conditions are described in ISO 9644.
7.4.3 Test procedure
Install the water meter in the measuring section in the test facility. Establish the flow and purge all air
from the test section. Ensure that the downstream static pressure is enough to prevent cavitation in the
meters or air release. Ensure that all air is removed from the pressure taps and transmitter connection
pipes. Ensure that the water is allowed to stabilize at the required temperature. While monitoring
the differential pressure, vary the flow between Q and Q . Record the flow rate showing the largest
1 3
pressure loss, Q , along with the measured pressure loss and water temperature. Normally, Q will be
t t
found to be equal to Q .
The maximum pressure loss should be measured with a maximum expanded uncertainty of 5 %, with a
coverage factor of k = 2.
7.4.4 Acceptance criteria
The pressure loss measurement at any flow rate within the rated operating conditions shall not exceed
the maximum value of the pressure loss corresponding to the class declared by the manufacturer.
7.5 Flow disturbance tests
Some kinds of water meters, for instance volumetric water meters, are considered insensitive to
installation conditions, so this test is not to be applied.
14 © ISO 2014 – All rights reserved

The manufacturer shall specify the flow profile disturbance sensitivity class for the water meter. This
class will never imply lengths longer than 15 DN upstream, and 5 DN downstream.
7.5.1 Object of the test
The object of the test is to verify that the water meter complies with the requirements in 6.3 of this
International Standard.
NOTE 1 The effects on the error of a water meter, of the presence of specified, common types of disturbed flow
upstream and downstream from the water meter are measured.
NOTE 2 Types 1 and 2 disturbance devices are used in the tests to create left-handed (sinistrorsum) and right-
handed (dextrorsum) rotational velocity profiles (swirl), respectively. The flow disturbance is of a type usually
found downstream from two 90° bends directly connected. A type 3 disturbance device creates an asymmetric
velocity profile usually found downstream from a protruding pipe joint or a gate valve not fully opened.
7.5.2 Preparation
In addition to the installation and operational requirements described in 7.3.2, the conditions described
in 7.5.3 also apply.
7.5.3 Test procedure
a) Using the Types 1, 2, and 3 flow disturbers specified in Annex B, determine the error of the water
meter at a flow rate between 0,9 Q and Q , for each one of the six installation conditions specified
3 3
in Figure 1.
b) During each test, hold all other influence factors at the reference conditions of 7.1.2.
Additional requirements:
c) For water meters installations where the manufacturer has specified installation lengths of straight
pipe of at least 15 × DN upstream and 5 × DN downstream from the water meter, no external flow
straighteners are allowed.
d) When a minimum straight pipe length of 5 × DN downstream from the water meter is specified by
the manufacturer, perform only tests for installation conditions 1, 3, and 5 shown in Figure 1.
e) Where water meter installations with external flow straighteners are to be used, the manufacturer
shall specify and deliver the straightener together with the water meters to accommodate testing
of its technical characteristics and its position in the installation relative to the water meter.
f) A device within a water meter having flow straightening functions is not considered to be a
“straightener” in the context of these tests.
g) The straight lengths upstream and downstream of the meter depend on the flow profile sensitivity
class of the meter and shall be in accordance with Tables 3 and 4 respectively.
7.5.4 Acceptance criteria
The relative error of the meter shall not exceed the applicable maximum permissible error for any of the
flow disturbance test.
Key
16 © ISO 2014 – All rights reserved

1 type 1 disturber
2 water meter
3 straight lengths
4 straightener
5 type 2 disturber
6 type 3 disturber
Figure 1 — Flow disturbance scheme
7.6 Reverse flow test
7.6.1 Object of the test
To verify that the meter satisfies the requirement of 5.5 in this International Standard when reverse
flow occurs.
Meters which are designed to measure reverse flow shall record the reverse flow volume accurately.
Meters which allow reverse flow, but which are not designed to measure it, shall be subjected to reverse
flow. The error shall subsequently be measured for forward flow, to check that there is no degradation
in metrological performance caused by reverse flow.
Meters which are designed to prevent reverse flow (e.g. by means of an integral non-return valve) are
subjected to the application of the maximum admissible pressure of the meter applied to the outlet
connection and the measurement errors are subsequently measured for forward flow to ensure that
there is no degradation in metrological performance caused by the pressure acting on the meter.
7.6.2 Preparation
The installation and operational requirements described in 7.3.2 shall apply.
7.6.3 Test procedure
7.6.3.1 Meters designed to measure reverse flow
a) Measure the error of at least one meter at each of the following reverse flow rates:
1) Between Q and 1,1 Q
1 1;
2) Between Q and 1,1 Q
2 2;
3) Between 0,9 Q and Q
3 3.
b) During each test, all other influence factors shall be maintained at reference conditions.
c) Calculate the error for each flow rate.
d) In addition, the following tests shall be carried out: pressure loss test (7.4), flow disturbance test
(7.5) and endurance test (7.7).
7.6.3.2 Water meters not designed to measure reverse flows
a) Subject the meter to a reverse flow of 0,9 Q for 1 min.
b) Measure the error of at least one meter at each of the following forward flow rates:
1) Between Q and 1,1 Q ;
1 1
2) Between Q and 1,1 Q ;
2 2
3) Between 0,9 Q and Q .
3 3
c) During each test, all other influence factors shall be maintained at reference conditions.
d) Calculate the error for each flow rate.
7.6.3.3 Water meters which prevent reverse flows
a) Meters which prevent reverse flow should be subjected to the maximum admissible pressure in the
reverse flow direction for 1 min.
b) Check that there is no significant leak past the valve.
b) Measure the error of at least one meter at each of the following forward flow rates:
1) Between Q and 1,1 Q ;
1 1
and 1,1 Q ;
2) Between Q
2 2
3) Between 0,9 Q and Q .
3 3
c) During each test, all other influence factors shall be maintained at reference conditions.
d) Calculate the relative error for each flow rate.
7.6.4 Acceptance criteria
In the tests described in 7.6.3.1, 7.6.3.2, and 7.6.3.3, the error of the water meter shall not exceed the
applicable maximum permissible error.
7.7 Endurance tests
7.7.1 Durability test
Table 7 — Endurance test
Dura-
Period of
Test water tion
Tempera- Permanent Test Number of Dura- opera-
t
...