EN ISO 20486:2018

SLOVENSKI STANDARD
01-julij-2018
1DGRPHãþD
SIST EN 13192:2002
SIST EN 13192:2002/AC:2004
1HSRUXãLWYHQRSUHVNXãDQMH3UHLVNDYDWHVQRVWL8PHUMDQMHUHIHUHQþQHWHVQRVWL]D
SOLQ,62
Non-destructive testing - Leak testing - Calibration of reference leaks for gases (ISO
20486:2017)
Zerstörungsfreie Prüfung - Dichtheitsprüfung - Kalibrieren von Referenzlecks für Gase
(ISO 20486:2017)
Essais non destructifs - Contrôle d'étanchéité - Étalonnage des fuites de référence des
gaz (ISO 20486:2017)
Ta slovenski standard je istoveten z: EN ISO 20486:2018
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20486
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2018
EUROPÄISCHE NORM
ICS 19.100 Supersedes EN 13192:2001
English Version
Non-destructive testing - Leak testing - Calibration of
reference leaks for gases (ISO 20486:2017)
Essais non destructifs - Contrôle d'étanchéité - Zerstörungsfreie Prüfung - Dichtheitsprüfung -
Étalonnage des fuites de référence des gaz (ISO Kalibrieren von Referenzlecks für Gase (ISO
20486:2017) 20486:2017)
This European Standard was approved by CEN on 23 December 2017.

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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20486:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 20486:2018) has been prepared by Technical Committee ISO/TC 135 "Non-
destructive testing" in collaboration with Technical Committee CEN/TC 138 “Non-destructive testing”,
the secretariat of which is held by AFNOR.
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 August 2018, and conflicting national standards shall
be withdrawn at the latest by August 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 13192:2001.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 20486:2017 has been approved by CEN as EN ISO 20486:2018 without any modification.

INTERNATIONAL ISO
STANDARD 20486
First edition
2017-12
Non-destructive testing — Leak
testing — Calibration of reference
leaks for gases
Essais non destructifs — Contrôle d'étanchéité — Étalonnage des
fuites de référence des gaz
Reference number
ISO 20486:2017(E)
©
ISO 2017
ISO 20486:2017(E)
© ISO 2017, Published in Switzerland
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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 20486:2017(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Nominal leakage rates . 3
5 Classification of leaks . 3
5.1 Permeation leak . 3
5.2 Conductance leaks . 3
5.2.1 Capillary leak . 3
5.2.2 Aperture leak (orifice) . 4
5.2.3 Compressed powder leak . 4
6 Calibration by comparison . 4
6.1 Methods A, A , B and B .
s s 4
6.2 Applicability of comparison methods . 4
6.3 Preparation of leaks and apparatus . 5
6.3.1 Leak detector . 5
6.3.2 Connection to the leak detector . 5
6.3.3 Temperature accommodation . 7
6.4 Measurement . 7
6.4.1 Set-up . 7
6.4.2 General measurement sequence . 7
6.5 Evaluation for methods A, A , B and B (Comparison) . 8
s s
6.5.1 Determination of leakage rate . 8
6.5.2 Influence factors to measurement uncertainty . 9
7 Volumetric calibration.10
7.1 Direct flow (Method C) .10
7.1.1 General.10
7.1.2 Equipment .10
7.1.3 Preparation of leaks and apparatus .10
7.1.4 Measurement .11
7.1.5 Evaluation for Method C (direct flow measurement) .13
7.2 Leak measurement under water (Method D) .14
7.2.1 General.14
7.2.2 Equipment .14
7.2.3 Preparation of leaks and apparatus .14
7.2.4 Measurement .15
7.2.5 Evaluation for Method D .16
7.2.6 Influence factors to measurement uncertainty .17
7.3 Calibration by (volumetric) gas meter (Method E) .17
7.3.1 General.17
7.3.2 Equipment .18
7.3.3 Preparation of leaks and apparatus .18
7.3.4 Measurement .18
7.3.5 Evaluation for Method E (gas meter) .18
7.3.6 Influence factors to measurement uncertainty .19
7.4 Calibration by pressure change in a known volume (Method F) .19
7.4.1 General.19
7.4.2 Preparation of leaks and apparatus .20
7.4.3 Measurement .22
7.4.4 Special situation in vacuum chambers .23
7.4.5 Evaluation for Method F (pressure change) .25
7.4.6 Influence factors to measurement uncertainty .25
ISO 20486:2017(E)
7.5 Calibration by volume change at constant pressure (Method G) .26
7.5.1 Equipment .26
7.5.2 Preparation of leaks and apparatus .26
7.5.3 Measurement .26
7.5.4 Evaluation for Method G (volume change at constant pressure).27
8 General influences .28
9 Report .28
10 Labelling of reference leaks .29
11 Handling of reference leaks .29
11.1 General .29
11.2 Permeation leaks (normally with reservoir fitted the leak outlet) .29
11.3 Conductance leaks (normally without reservoir) .29
Annex A (informative) Calculation of leakage rate decrease due to tracer gas depletion in
the reservoir .30
Bibliography .32
iv © ISO 2017 – All rights reserved

ISO 20486:2017(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.
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 voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing,
Subcommittee SC 6, Leak testing.
INTERNATIONAL STANDARD ISO 20486:2017(E)
Non-destructive testing — Leak testing — Calibration of
reference leaks for gases
1 Scope
This document specifies the calibration of those leaks that are used for the adjustment of leak detectors
for the determination of leakage rate in everyday use. One type of calibration method is a comparison
with a reference leak. In this way, the leaks used for routine use become traceable to a primary standard.
In other calibration methods, the value of vapour pressure was measured directly or calculated over a
known volume.
The comparison procedures are preferably applicable to helium leaks, because this test gas can be
selectively measured by a mass spectrometer leak detector (MSLD) (the definition of MSLD is given in
ISO 20484).
Calibration by comparison (see methods A, A , B and B below) with known reference leaks is easily
s s
−7 3
possible for leaks with reservoir and leakage rates below 10 Pa·m /s.
Figure 1 gives an overview of the different recommended calibration methods.
a) Calibration by comparison
ISO 20486:2017(E)
b) Calibration by direct measurement
Key
X leakage rate in Pa·m /s C Method C
A Method A D Method D
B Method B E Method E
A Method A F Method F
s s
B Method B G Method G
s s
normal range possible range
Figure 1 — Calibration ranges
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 20484, Non-destructive testing — Leak testing — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20484 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
2 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
3.1
unknown leak
leak having a stable and repeatable leakage rate of known order of magnitude that can be determined
by calibration
3.2
reference leak
calibrated leak which may be used to calibrate another leak
Note 1 to entry: The uncertainty of the reference leak is lower than the required uncertainty of the leak to be
calibrated.
3.3
calibration
set of operations which establish, under specified conditions, the relationship between leakage rate
values represented by an unknown leak and the corresponding known values of the leakage rate
Note 1 to entry: In the case of calibration by comparison, the known values of the leakage rate are represented by
a reference leak.
Note 2 to entry: Normally, the result of a calibration is given as the leakage rate value for the reference leak with
a standard uncertainty.
3.4
nominal leakage rate
leakage rate of a leak calculated for specified reference conditions
Note 1 to entry: In leak detection, leakage rates are commonly given in units of pV-throughput (Pa·m /s, mbar l/s,
Std cm /min). These are only a precise measure of gas flow if the temperature is given and kept constant. Flow
units such as mass flow (g/y) or molar flow (mol/s) are sometimes used to overcome this problem.
4 Nominal leakage rates
Calibrated leaks are only comparable under the same reference conditions. Nominal leakage rates shall
be used for comparison. Recommended reference conditions are:
— Ambient temperature: 20 °C
— Atmospheric exhaust pressure: 1 000 mbar
— Vacuum exhaust pressure: < 100 mbar
The reference inlet pressure is given by the leak reservoir pressure or the application requirement.
5 Classification of leaks
5.1 Permeation leak
This type of leak is normally made with a tracer gas reservoir. It has the best long-term stability but an
appreciable temperature coefficient (approximately 3,5 %/K). Typical leakage rates are in the range
−10 3 −4 3
from 10 Pa·m /s to 10 Pa·m /s.
5.2 Conductance leaks
5.2.1 Capillary leak
This type of leak is available with or without a tracer gas reservoir. It has a low temperature coefficient
(approximately 0,3 %/K) but easily blocks if not handled with care. Typical leakage rates are greater
−7 3
than 10 Pa·m /s.
ISO 20486:2017(E)
5.2.2 Aperture leak (orifice)
Orifices are seldom used as reference leaks in practice, as they are difficult to manufacture and even
more prone to blocking than capillaries.
NOTE Critical flow orifices are a form of aperture leak that is commonly found in industry, but are out of the
scope of this document.
5.2.3 Compressed powder leak
This type of leak uses metal powder compressed into a tube. They are usually offered without reservoir.
They are used for routine check of the sensitivity of leak detectors but they are not stable enough to be
used as calibrated leaks. Their suitability depends on how well controlled the storage and operating
conditions are, and on the required uncertainty.
6 Calibration by comparison
6.1 Methods A, A , B and B
s s
There are two ways of calibrating leaks by comparison with known reference leaks. Both methods
require the knowledge of the order of magnitude of the leakage rate to be measured. The methods
differ in using one or two reference leaks, resulting in different uncertainties of measurement. In the
following, the two methods are designated as A and B:
— Method A: Comparison to one reference leak normally with a leakage rate of the same order of
magnitude, calibration with vacuum method.
— Method A : Comparison to one reference leak normally with a leakage rate of the same order of
s
magnitude, calibration with sniffing method.
— Method B: Comparison to two reference leaks with leakage rates normally lying on either side of the
unknown leakage rate, calibration with vacuum method.
— Method B : Comparison to two reference leaks with leakage rates normally lying on either side of
s
the unknown leakage rate. Calibration with sniffing method.
Method A is most suitable for use on site as only one reference leak is used. It is generally applicable
but is most reliable when the leakage rate of the unknown is close to that of the reference leak. This is
because the measurement uncertainty is directly dependent on the linearity of the leak detector in use.
As the linearity error cannot be measured independently, it needs to be estimated. To keep the linearity
error small, the operating characteristics of leak detector should not change during calibration (e.g.
automatic ranging should be disabled).
For more precise calibrations, where a more reliable measure of uncertainty is required or if a reference
leak with a leakage rate close to the unknown is not available Method B should be used. By the use of
two reference leaks, the non-linearity of the leak detector is accounted for.
6.2 Applicability of comparison methods
Since comparison of leaks is not a fundamental measurement method, it relies on the stability of the
transfer device and cleanliness of the ambient gas atmosphere. Moreover, the temperature dependence
of the reference and unknown leaks shall be taken into account.
The most stable and clean conditions are achieved for leaks with exhaust into vacuum and a mass
spectrometer leak detector as transfer device measuring the partial pressure generated by the leaks in
vacuum. Under these conditions, all interfering background gases are reduced to a minimum so that the
zero point of the transfer device is defined and stable.
4 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
For leaks with exhaust into the atmosphere and measurement by sniffing gas, more conditions shall be
controlled. These are:
— the background level of tracer gas shall be as low as possible and as stable as possible;
— the total gas flow rate of the sniffer shall be high enough to take up the total tracer gas flow out of
the leak;
— the aspiration of the sniffer (the coupling to the leak exhaust) shall be of suitable geometry to make
sure that the atmospheric gas flow across the leak exhaust takes up the whole tracer gas flow from
the leak opening.
As a consequence, the measurement uncertainty is appreciably higher for sniffer leaks than for
vacuum leaks.
Methods by comparison are therefore applicable but not preferable for the calibration of sniffer leaks
(with exhaust to atmosphere).
6.3 Preparation of leaks and apparatus
6.3.1 Leak detector
The leak detector (LD) used as a transfer device shall be set up according to the manufacturer’s manual.
The warm-up time shall be at least 2 h.
6.3.2 Connection to the leak detector
The reference and unknown leaks are connected to the leak detector used as the transfer instrument.
The connection shall be kept continuously until the measurement is completed. This includes thermal
[1]
accommodation .
In the case of vacuum leaks, they are connected to the inlet flange and pumped with their valves (if any)
open for at least 30 min to remove any tracer gas that can have accumulated in seals or valves. For the
calibration of more than one leak, a separate pumping system and set of valves is useful to keep all the
leaks pumped until they are measured.
ISO 20486:2017(E)
Key
1 transfer device (leak detector)
2 test port
3 rig
4 leaks to be calibrated and reference leak
5 hoods for thermal stability
Figure 2 — Coupling of leaks to the leak detector
In the case of sniffer leaks, the connection to the leak detector sniffing tip is made by an adapter which
makes a tight connection to the leak outlet and enables atmospheric air to be continuously sucked
across the leak exhaust via an air inlet (see Key item 3 in Figure 2), so that the whole leak gas flow
is taken up by the sniffer tip. The air inlet opening shall not throttle the free flow of air to maintain
atmospheric pressure in front of the sniffer tip. See Figure 3.
6 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
Key
1 gasket 4 test leak with leak opening
2 sniffer tip 5 adapter body with gasket
3 air inlet 6 sniffer opening with cross-wise slot
Figure 3 — Example for a coupling adapter for sniffer leaks
6.3.3 Temperature accommodation
The unknown leak and the reference leak(s) for the comparison shall be stored in the same room where
the test is to be carried out for at least 12 h to allow for temperature equilibration (an air-conditioned
room is not necessary if there are no rapid temperature changes. Because of temperature fluctuations,
an air-conditioning system can even increase the measurement uncertainty). Vacuum leaks,
connected to the LD shall be pumped during the phase of thermal accommodation. After temperature
accommodation, to prevent any temperature changes during measurement, thermally insulating hoods
(made of plastic foam or similar material) should be put over the leaks.
6.4 Measurement
6.4.1 Set-up
It is important to ensure that the effective pumping speed at the leak detector inlet for vacuum leaks,
respectively the sniffer gas flow for overpressure leaks, is not changed during the measurements.
If possible, either with the leak detector or in an auxiliary device, a long averaging time may be used to
decrease the statistical measurement uncertainty.
All the measurement instruments should be adjusted in such a way that they give nearly full-scale
deflections for the biggest leak.
6.4.2 General measurement sequence
Generally, each reading shall be obtained only after the signal of the transfer instrument has stabilized.
A sufficient number of readings shall be taken to achieve the lowest possible statistical uncertainty.
ISO 20486:2017(E)
This way, a measure of statistical deviation can also be found. The general sequence of measurements
is as follows:
a) zero signal determination: all valves closed for vacuum leaks, respectively sniffer tip in pure
ambient air for sniffing leaks;
b) connect reference leak No. 1, wait for steady flow and measure the resulting output signal
(Method A, A , B and B );
s s
c) disconnect reference leak No.1;
d) connect reference leak No. 2, wait for steady flow and measure the resulting output signal (only
Method B and B );
s
e) disconnect reference leak No. 2;
f) connect unknown leaks, wait for steady flow and measure the resulting output signal;
g) repeat steps a) to f) at least three times.
Leak valves should be kept closed for as short a time as possible to prevent extensive helium
accumulation resulting in long equilibration time.
6.5 Evaluation for methods A, A , B and B (Comparison)
s s
6.5.1 Determination of leakage rate
6.5.1.1 Method A and A : Result of comparison to one reference leak
s
Formula (1a) is used to calculate the unknown leakage rate, Q , from the reading, R , of the reference
u ref
leak with leakage rate, Q , and the reading, R , of the unknown leak:
ref u
R
u
QQ= (1a)
uref
R
ref
This formula is only valid, if the temperature coefficients and the temperatures of all leaks are equal.
Otherwise, Formula (1b) shall be used:
 
RT1+⋅α Δ
()
uref ref
QQ=⋅ (1b)
 
uref
RT1+⋅α Δ
()
 
refu u
 
where
Q , Q are the leakage rates of the reference and unknown leak, respectively;
ref u
R , the readings of the reference and unknown leak, respectively;
ref Ru
α , α are the temperature coefficients of the reference and unknown leak, respectively;
ref u
ΔT , ΔT are the departures of the temperature of the leaks from the reference temperature of
ref u
the reference and unknown leak, respectively.
The readings can be in any consistent units, as only ratios are considered.
NOTE 1 The readings (R and R ) are obtained from the leak detector display as the difference of the output
ref u
signals with leak connected and disconnected (respectively, valve opened and closed).
NOTE 2 The temperature coefficient of the reference leak is normally stated. If the temperature coefficient of
the unknown leak is not given, it can be assumed that it is approximately 3,5 %/K for a quartz permeation leak,
and 0,3 %/K for conductance type leaks in viscous flow mode.
8 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
6.5.1.2 Method B and B : Result of comparison to two reference leaks
s
To keep this procedure practical, only the case of equal temperature coefficients and the same
temperature difference between each reference leak and its calibration reference temperature is
considered. In this case, the simplified Formula (2) holds. See Figure 4.
RR− 
u 1
QQ=−Q +Q (2)
()
 
u2 1 1
RR−
 
where
Q , Q , Q are leakage rates of the unknown leak and the reference leaks 1 and 2, respectively;
u 1 2
R , R , R are readings for the unknown leak and the reference leaks 1 and 2, respectively.
u 1 2
Key
A reference leak 1
B unknown leak
C reference leak 2
R reading
Q leakage rate
NOTE Q is the leak with the smaller rate, Q the leak with the larger rate. Q , the leakage rate of the
1 2 u
unknown leak to be calibrated, lies between these two known leaks.
Figure 4 — Two-point calibration of a leak
6.5.2 Influence factors to measurement uncertainty
The calibration is mainly influenced by the following factors:
— uncertainty of the reference leak(s);
— ambient temperature (all leaks at the same temperature level);
— linearity of the leak detector.
The uncertainty shall be calculated according to common guidelines (see [2]).
ISO 20486:2017(E)
7 Volumetric calibration
7.1 Direct flow (Method C)
7.1.1 General
−5 3 3
This method is applicable to conductance leaks in the range of 10 Pa·m /s (~0,006 Std cm /min) to
3 3 −6 3 3 −5 3
0,2 Pa·m /s (~100 Std cm /min). Leaks from 10 Pa·m /s (~0,000 6 Std cm /min) to 10 Pa·m /s
(~0,006 Std cm /min) can be calibrated, but with a rather large uncertainty. In that range, if a suitable
reference leak is available, methods A or B should be employed to give lower uncertainty.
Two types of pressure and flow conditions shall be considered:
— flow from pressure to atmosphere (see 7.1.4.1);
— flow from atmosphere to vacuum (see 7.1.4.2).
The third possible flow condition, pressure to vacuum, cannot be measured with Method C (if this is
required, a calibration with tracer gas according Method A or B with a suitable MSLD or a calibration
according to Method F or G needs to be made.)
7.1.2 Equipment
To calibrate a leak by measurement of capillary flow according to Method C described in 7.1.4, a
calibrated glass tube (preferably with a suitable vent valve at one end, see Figures 5 and 6) is necessary.
An indicator fluid (normally water with some surfactant added or special oils) is used to produce the
measurement slug in the capillary.
To measure the time of slug movement, a timer or stopwatch is needed. Instruments based on the timed
movements of a film in a tube are also available, e.g. a bubble flow meter.
As conductance leak elements normally have no tracer gas reservoir, a separate tracer gas supply is
needed or calibration may be performed with filtered, oil free and dry atmospheric air.
7.1.3 Preparation of leaks and apparatus
7.1.3.1 Temperature accommodation
The unknown leak and the calibrated capillary shall be stored in the room where the test is to be carried
out for at least 12 h to allow for temperature equilibration (an air-conditioned room is not necessary
if there are no rapid temperature changes. Because of temperature oscillations, an air-conditioning
system can even increase the measurement uncertainty).
7.1.3.2 Connection of leak to capillary tube
The capillary tube and vent valve shall be cleaned with alcohol and purged with pressurized air
to remove any dirt from the surfaces that can disturb the free movement of the liquid slug during
measurement. The connection between the leak and the capillary tube shall be made with a thick
elastomer connecting hose fitting tightly on both the leak outlet and the vent valve of the capillary. The
smaller the unknown leak, the more important it is to keep all dead volumes as small as possible to
reduce measurement errors.
Pressure to atmosphere
In this case, the leak inlet is connected to the tracer gas supply and the outlet to the capillary tube. The
capillary tube is open to atmosphere at the other end (see Figure 5).
10 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
Atmosphere to vacuum
In this case, the leak outlet is connected to a vacuum and the inlet to the capillary tube. The capillary
inlet is open to atmospheric pressure (see Figure 6).
If standard leakage rates are required, the outlet absolute pressure shall be less than 100 Pa.
7.1.4 Measurement
7.1.4.1 Pressure to atmosphere
The measurement is performed according to the following procedure:
a) maintain the gas flow through the leak to be calibrated for a minimum of 1 h at nominal pressure.
All connectors shall be dry and clean;
b) dip the open end of the capillary into the indicator fluid to produce a liquid slug;
c) draw this slug slowly up the capillary to the other end by carefully pumping via the vent valve (if there
is no vent valve, disconnect the capillary, dip the tip into the indicator fluid and replace the slug);
d) close the vent valve (if present) and time the movement of the trailing edge of the slug for a
convenient distance (minimum 1,5 × expected flow rate);
e) reposition the slug (see above) and repeat steps a) to d) at least three times. The repeatability of the
measurements should be within ±2 %.
Key
1 gas pressure from reservoir 7 atmosphere
2 unknown leak 8 indicating slug
3 optional pump connection (to initialize the slug position) 9 calibration marks
4 optional vent valve 10 connecting tubes
5 trailing edge of slug 11 zero space
6 inside diameter capillary tube
Figure 5 — Set-up for Method C measurement: pressure to atmosphere
ISO 20486:2017(E)
7.1.4.2 Atmosphere to vacuum
The measurement is performed according to the following procedure:
a) maintain the gas flow through the leak to be calibrated for a minimum of 1 hour at nominal
pressure. All connectors shall be dry and clean;
b) dip the open end of the capillary into the indicator fluid to produce a liquid slug;
c) close the vent valve and time the movement of the leading edge of the slug over a convenient
distance (minimum 1,5 × expected flow rate).
d) reposition the liquid slug to the end of the capillary again, using gas pressure via the vent valve;
e) repeat steps a) to d) at least three times. The repeatability of the measurements should be
within ±2 %.
Key
1 vacuum 7 atmosphere
2 unknown leak 8 indicating slug
3 gas fill connection 9 calibration marks
4 filling valve 10 connecting tubes
5 leading edge of slug 11 zero space
6 inside diameter capillary tube
Figure 6 — Set-up for Method C measurement: atmosphere to vacuum
12 © ISO 2017 – All rights reserved

ISO 20486:2017(E)
7.1.5 Evaluation for Method C (direct flow measurement)
7.1.5.1 Determination of leakage rate
The unknown leakage rate is given by:
ΔV
Qp=× (3)
pV TA
Δt
where
Q is the pV-throughput at test condition;
pV
p is the test pressure at leak exit;
TA
ΔV is the collected volume;
Δt is the collecting time.
Pressure-to-atmosphere measurements shall be corrected for the vapour pressure of the indicating
liquid, for the viscosity of the tracer gas and also for the influence of pressure and temperature. For the
nominal leakage rate, reference pressure and temperature are given in Clause 4. Formula (4) assumes
laminar flow in a round pipe (Hagen-Poiseuille). For each type of leak, it shall be checked whether
this assumption is applicable. Otherwise, it is necessary to calculate with an adequate formula or an
empirical correction.
The nominal leakage rate is calculated by Formula (4):
pp− p ×T p
η
refi,,nref out teesto, ut ref test,out
ref
QQ=× × × × (4)
NpV
η pT×
pp−−p
pp− ()
test refo, ut test
test,outvv,ref ,teest
test,,in test out
where
Q is the nominal leakage rate;
N
Q is the pV-throughput at test condition according to Formula (3);
pV
η is the viscosity of gas at reference conditions;
ref
η is the viscosity of gas at test conditions;
test
p is the reference pressure at leak entrance;
ref,in
p is the reference pressure at leak exit;
ref,out
p is the test pressure at leak entrance;
test,in
p is the test pressure at leak exit;
test,out
T is the reference temperature;
ref
T is the temperature at test conditions;
test
p is the vapour pressure at reference conditions;
v,ref
p is the vapour pressure at test condition.
v,test
ISO 20486:2017(E)
Atmosphere to vacuum measurement need not to be corrected for vapour pressure because, in this
situation, gas with high humidity is passing the leak.
The nominal leakage rate is given by:
pp− p ×T
η
refi,,nref out teesto, ut ref
ref
QQ=× × × (5)
NpV
η pT×
pp−
test refo, ut test
test,,in test out
7.1.5.2 Influence factors to measurement uncertainty
The calibration is mainly influenced by the following factors:
— test time;
— test volume;
— ambient pressure;
— ambient temperature;
— vapour pressure;
— test pressure.
The uncertainty shall be calculated according to common guidelines (see [2]).
7.2 Leak measurement under water (Method D)
7.2.1 General
3 3
This method is applicable to conductance leaks in the range of 0,2 Pa·m /s (~100 Std cm /mi
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