ISO 21360:2007

INTERNATIONAL ISO
STANDARD 21360
First edition
2007-06-01
Vacuum technology — Standard methods
for measuring vacuum-pump
performance — General description
Technique du vide — Méthodes normalisées pour mesurer les
performances des pompes à vide — Description générale

Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols and abbreviated terms . 3
5 Test Methods. 4
5.1 Volume flow rate (pumping speed) measurement with the throughput method . 4
5.2 Volume flow rate (pumping speed) measurement with the orifice method. 8
5.3 Volume flow rate (pumping speed) measurement with the pump-down method . 13
5.4 Measurement of the base pressure . 18
5.5 Measurement of the compression ratio and the critical backing pressure. 19
Annex A (informative) Mean free path of some important gases. 23
Annex B (informative) Measuring uncertainties. 24
Bibliography . 27

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 21360 was prepared by Technical Committee ISO/TC 112, Vacuum technology.
iv © ISO 2007 – All rights reserved

Introduction
This International Standard is a basic standard for measuring the performance data of vacuum pumps. The
methods described here are well known from existing national and international standards. In developing this
International Standard, the aim was to provide one single document containing the measurements of
performance data of vacuum pumps and to simplify the future development of specific vacuum pump
standards.
Specific vacuum pump standards will contain a suitable selection of measurement methods from this basic
standard in order to determine the performance data, limiting values and specific operational conditions on the
basis of the specific properties of the particular kind of pump. Whenever a discrepancy exists between the
basic standard and the specific standard, it is the specific standard which is valid.

INTERNATIONAL STANDARD ISO 21360:2007(E)

Vacuum technology — Standard methods for measuring
vacuum-pump performance — General description
1 Scope
This International Standard is a basic standard which defines three different methods for measuring the
volume flow rate and one method each for measuring the base pressure, the compression ratio and the critical
backing pressure of a vacuum pump.
The first method for measuring the volume flow rate (the throughput method) is the basic concept, in which a
steady gas flow is injected into the pump while the inlet pressure is measured. In practice, the measurement
of gas throughput may be complicated or inexact. For this reason, two other methods are described which
avoid the direct measurement of throughput.
The second method for measuring the volume flow rate (the orifice method) is used when there is very small
throughput occurring at very small inlet pressures (in the high and ultra-high vacuum). It is based on
measuring the ratio of pressures in a two-chamber test dome where the two chambers are separated by a wall
with a circular orifice.
The third method for measuring the volume flow rate (the pump-down method) is well-suited for automated
measurement. It is based on the evacuation of a large vessel. The volume flow rate is calculated from two
pressures, before and after a pumping interval, and from the volume of the test dome. Different effects, such
as leak and desorption rates, gas cooling by nearly isentropic expansion during the pumping interval and
increasing flow resistance in the connection line between test dome and pump caused by molecular flow at
low pressures, influence the results of the pressure measurement and the resulting volume flow rate.
The choice of the required measurement methods depends on the properties of the specific kinds of vacuum
pump, e.g. the measurement of the critical backing pressure is only necessary for vacuum pumps which need
a backing pump. All data that is measured on a vacuum pump but not described in this International Standard
(e.g. measurement of power consumption) is defined in the specific pump standard.
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 3529-1, Vacuum technology — Vocabulary — Part 1: General terms
ISO 3529-2, Vacuum technology — Vocabulary — Part 2: Vacuum pumps and related terms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3529-2 and the following apply.
3.1
volume flow rate
q
V
volume of gas which, under ideal conditions, flows from the test dome through the pump inlet per unit time
NOTE 1 For practical reasons, however, the volume flow rate of a given pump and for a given gas is conventionally
considered to be equal to the quotient of the throughput of this gas and of the equilibrium pressure at a given location. The
units adopted for the volume flow rate are cubic metres per hour (m /h) or litres per second (l/s).
NOTE 2 The term “pumping speed” and symbol “S” are often used instead of “volume flow rate”.
3.2
inlet pressure
p , p , p
1 d e
pressure at the inlet of the pump, measured at a defined location in the test dome
3.3
base pressure
p
b
pressure obtained in the test dome after conditioning the vacuum pump and the test dome
See 5.4.
NOTE The ultimate pressure is the value which the pressure in the test dome approaches asymptotically. It is the
lowest pressure obtainable with the pump, but there is no practical method of measurement or specification.
3.4
maximum working pressure
p
1max
highest pressure on the inlet side that the vacuum pump and the driving device can withstand for a prolonged
period of operation time without being damaged
3.5
backing pressure
p
pressure at the outlet of a vacuum pump
3.6
critical backing pressure
p
c
maximum backing pressure for which the conditions are defined in the instruction manual or in a specific
standard for the particular vacuum pump
3.7
compression ratio
K
ratio of the backing pressure, p , to the inlet pressure, p , of the vacuum pump without throughput, expressed
3 1
by the following equation:
p
K =
p
2 © ISO 2007 – All rights reserved

3.8
test dome
special vacuum vessel with precisely defined size, diameter and connection flanges on specified locations,
used for standard performance data measurements on vacuum pumps
3.9
throughput
Q
amount of gas flowing through a duct, expressed by the following equation:
pV
Qp==q
1 V
t
where
p is the (high) vacuum pressure on the inlet;
q is the volume flow rate of the test pump;
V
t is time;
V is the volume of the test dome.
3.10
standard gas flow rate
q
Vstd
volume flow rate at standard reference conditions for gases in accordance with ISO 3529-1
4 Symbols and abbreviated terms
Symbol Designation Unit
a
inner diameter of the connection pipe between test pump and m
quick-acting valve (items 3 and 5 in Figure 6)
A cross-section of the connection pipe between test pump and
m
quick-acting valve (items 3 and 5 in Figure 6)
3 3
C conductance
m /s (= 10 l/s)
d diameter of orifice m
D inner diameter of test dome m

D nominal diameter of test dome m

N
K compression ratio of vacuum pump with zero throughput —

l length of the connection pipe between test pump and m

quick-acting valve (items 3 and 5 in Figure 6)
mean free path m
l
L thickness of the orifice wall at the orifice diameter m
M molar mass of gas kg/mol
p 101 325 Pa in accordance with ISO 3529-1 Pa
p
(high) vacuum pressure on inlet Pa (or mbar)
p maximum working pressure on inlet Pa (or mbar)
1max
p vacuum pressure in backing line Pa (or mbar)
p , p , p pressures in the test dome for the pump-down method, Pa (or mbar)
t1 t2 t3
measured before and after time intervals ∆t , ∆t , ∆t
1 2 3
p , p ,.p base pressures Pa (or mbar)
b1 b2 b3
p critical backing pressure Pa (or mbar)
c
p , p pressures in the test dome for the orifice method Pa (or mbar)
d e
Q gas throughput of vacuum pump Pa·l/s (or mbar·l/s)
Q test gas load Pa·l/s (or mbar·l/s)
r
q volume flow rate of test pump
l/s (or m /h)
V
q volume flow rate of backing pump
l/s (or m /h)
VB
q volume flow rate at standard reference conditions for gases in
sccm (or cm /min)
Vsccm
accordance with ISO 3529-1
q volume flow rate at standard reference conditions for gases in
l/s (or m /h)
Vstd
accordance with ISO 3529-1
Q maximum gas throughput of vacuum pump which the pump can Pa·l/s (or mbar·l/s)
max
withstand without damage
R ideal gas constant 8,314 J/(mol·K)
T
thermodynamic temperature K
T 273,15 K in accordance with ISO 3529-1 K
T temperature of the test dome K
D
T temperature of the flow meter K
f
u measurement uncertainty —
V
volume of the test dome
l, m
V volume of connection pipe between test pump and quick-acting
l, m
i
valve (items 3 and 5 in Figure 6)
5 Test Methods
5.1 Volume flow rate (pumping speed) measurement with the throughput method
5.1.1 General
The throughput method is the one most used for vacuum pumps and is applicable for all pressure ranges and
pump sizes where flow meters for the gas throughput measurements are available with sufficient accuracy.
The gas flow measuring ranges shall be chosen by multiplying the expected volume flow rate with the
maximum and minimum working pressure of the test pump.
All measuring devices shall be calibrated either:
a) in a traceable way to a vacuum primary or to a national standard, or
b) by means of instruments of absolute measure which are traceable to the SI units and to which
measurement uncertainties can be attributed.
In the case of calibrated measuring instruments, there should exist a calibration certificate in accordance with
ISO/IEC 17025.
4 © ISO 2007 – All rights reserved

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