ISO 27895:2009

INTERNATIONAL ISO
STANDARD 27895
First edition
2009-12-15


Vacuum technology — Valves — Leak
test
Technique du vide — Vannes à vide — Essai d'étanchéité des vannes
à vide




Reference number
ISO 27895:2009(E)
©
ISO 2009

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ISO 27895:2009(E)
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ii © ISO 2009 – All rights reserved

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ISO 27895:2009(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Symbols.4
5 Requirements.5
6 Test methods .5
6.1 Valve seat leak test.5
6.2 Valve body leak test .7
6.3 Leak test on minimum and maximum pressures of compressed air for pneumatic valve
operation (optional).9
6.4 Leak test on minimum and maximum torques of manual valve (optional) .9
6.5 Leak test in operating temperature range (optional).9
6.6 Leak test after baking (optional).9
7 Test report.9
Bibliography.11

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ISO 27895:2009(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 27895 was prepared by Technical Committee ISO/TC 112, Vacuum technology.

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ISO 27895:2009(E)
Introduction
Vacuum valves are the most common parts in vacuum systems. Valve manufacturers provide technical data
for vacuum valves based on their own test methods and end users use these data to select valves. However,
until the time of publication, there has been no International Standard specifying leak test methods for vacuum
valves even though leak rate data are among the most fundamental. For example, the leak rate of the valve
may vary in the time interval between gas filling and leak testing.
There are three different types of leak: a) real leaks, i.e. macroscopic cracks or holes allowing gases to pass
through; b) virtual leaks, caused by outgassing of volatile material inside a vacuum system or trapped volume;
c) permeation leaks, i.e. microscopic holes of diameter comparable to that of an atom, which occur throughout
the construction material, e.g. in elastomers.
Virtual leaks are not measurable by the leak test method specified in this International Standard. Valve design
and the materials used should therefore be chosen to minimize the risk of virtual leaks occurring.
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INTERNATIONAL STANDARD ISO 27895:2009(E)

Vacuum technology — Valves — Leak test
1 Scope
This International Standard specifies methods for the leak testing of vacuum valves used for control of gas
flow or vacuum pressure in a vacuum system. It is applicable to vacuum valves that can be closed to leak
−5 3
rates less than 1 × 10 Pa m /s for trace gas. The methods employ a sealing arrangement for the valve body,
which is also specified in this International Standard. The methods are suitable for the verification of valve
specifications.
A valve leak rate less than the nominal leak rate specified by the manufacturer during and after the operation
enables the specification of such valve operating conditions as operating pressure range, permissible
pressure difference between ports, bake-out temperature or operating temperature, and life cycle.
NOTE 1 The data for large valves and valves without a valve body can vary from those obtained during delivery
inspection depending on the accuracy of the attachment surface of the vacuum device.
NOTE 2 The data obtained from this procedure is based on the testing conducted on an individual unit of a vacuum
valve and they can be different from those obtained during delivery inspection if the test is performed with the valve
incorporated into the equipment.
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 3530, Vacuum technology — Mass-spectrometer-type leak detector calibration
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
leak rate
q
〈vacuum valve technology〉 throughput of a trace gas, which passes through a crack, hole or gap in the wall,
seat or sealing material of a valve under specific conditions
NOTE 1 Adapted from ISO 3530:1979, 2.5.1.
NOTE 2 The leak rate is expressed in pascal cubic metres per second.
NOTE 3 The leak rate of the trace gas can be measured using a mass spectrometer-type leak detector. The leak rate
depends on type of gas, pressure difference, and temperature.
NOTE 4 The definitions standard air leak rate (3.2) and equivalent standard air leak rate (3.3) are more specific.
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ISO 27895:2009(E)
3.2
standard air leak rate
throughput, through an opening such as a crack or hole, of atmospheric air having a dew point of less than
−25 °C under standard conditions: an inlet pressure of (100 ± 5) kPa; an outlet pressure of less than 1 kPa;
and a temperature of (23 ± 7) °C
NOTE 1 Adapted from ISO 3530:1979, 2.5.2.
NOTE 2 The standard conditions are taken from ISO 3530.
3.3
equivalent standard air leak rate
−7 3
short-path leaks of the molecular type having standard air leak rates of less than 10 Pa m /s
EXAMPLE Helium (relative atomic mass 4) passes through such leaks more rapidly than air (average relative
molecular mass 29,0), and a given flow rate of helium corresponds to a smaller flow rate of air.
1/2
NOTE 1 “Equivalent standard air leak rate” is taken as (4/29) = 0,37 times the helium leak rate under the standard
conditions specified in ISO 3530.
NOTE 2 Adapted from ISO 3530:1979, 2.5.3.
3.4
trace gas
gas used to detect leaks
NOTE Mass-spectrometer-type leak detectors are used as the leak measurement instrument. If a helium mixture is
used, the leak rate is reported as a helium-equivalent value.
3.5
operating pressure
p
o
〈vacuum valve technology〉 pressure range for a valve in working condition
NOTE If a pressure is within the operating pressure range, the valve can have a leak rate smaller than that specified by
the manufacturer.
3.6
maximum operating pressure
p
o, max
〈vacuum valve technology〉 highest pressure at which the valve operates within its specifications
3.7 Pressure difference
NOTE 1 Figures 1 and 2 show schematic diagrams of angle valves and gate valves, respectively.
NOTE 2 Manufacturers of bellow-sealed angle valves often specify a maximum pressure difference separated as
differential pressures in the opening and closing directions. Usually, the critical case is the differential pressure in the
opening direction (p at “vacuum” and p at maximum pressure).
1 2
3.7.1
pressure difference
∆p
〈conventional angle and gate valves〉 pressure difference between p and p , where p is the pressure at the
1 2 2
space toward the valve disc with elastomer on the valve seat and p is the pressure of the opposite side within
1
the valve
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ISO 27895:2009(E)
3.7.2
pressure difference
∆p
〈bellow-sealed angle valves〉 pressure difference between p and p , where in the opening direction p is the
1 2 1
residual pressure at “vacuum” and p is the maximum pressure
2

Key
1 port A
2 port B
Figure 1 — Angle valve

Key
1 port A
2 port B
Figure 2 — Gate valve
3.8
maximum pressure difference
∆p
max
greatest pressure difference at which the valve can operate normally
NOTE If a pressure difference is lower than ∆p , the valve can have a leak rate smaller than that specified by the
max
manufacturer.
3.9
pressure range of compressed air for a pneumatic valve
p
p
pressure range of the compressed air specified by the manufacturer for a pneumatic valve closed or opened
by compressed air
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ISO 27895:2009(E)
NOTE The compressed air pressure can be specified not only as an absolute pressure but also as a pressure
relative to atmospheric, i.e. the gauge pressure.
3.10
torque range for valves with an operating torque specified
τ
torque range specified by the manufacturer for a valve operated by torque wrench
3.11
operating temperature
T
o
temperature at which the valve operates under normal conditions
NOTE An operating temperature range is specified by the manufacturer, within which a valve can be operated under
normal working conditions with a leak rate smaller than that specified by the manufacturer.
3.12
baking temperature
T
b
temperature at which the va
...