ISO/TR 12942:2012

TECHNICAL ISO/TR
REPORT 12942
First edition
2012-09-01

Compressors — Classification —
Complementary information to ISO 5390
Compresseurs — Classification — Information complémentaire à
l'ISO 5390




Reference number
ISO/TR 12942:2012(E)
©
ISO 2012

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ISO/TR 12942:2012(E)

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ii © ISO 2012 – All rights reserved

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ISO/TR 12942:2012(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Design classes.1
2.1 General .1
2.2 Classification by equipment type .3
2.3 Classification of compressor apparatuses by operation principles.3
2.4 Classification of compressor machines by operation principles .5
2.5 Design classes of compressor machines.6
3 Functional classes of the compressor equipment, terms and definitions.22
3.1 General .22
3.2 Basic functional classes of compressor machines.23
3.3 Formation principles of derivative functional classes for compressor machines.27
3.4 Functional classes of compressor apparatuses.32
4 Design classes of the aggregated compressor equipment, terms and definitions.34
4.1 General .34
4.2 Design classes of geared mechanical compressors.39
4.3 Design classes of driver-compressors .40
4.4 Design classes of geared driver-compressors .46
4.5 Design and service-duty classes of compressor plants .48
4.6 Design classes of packaged compressor plants .51
Annex A (informative) Design, functional and service-duty classification.54
Bibliography.59

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ISO/TR 12942:2012(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.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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/TR 12942 was prepared by Technical Committee ISO/TC 118, Compressors and pneumatic tools,
machines and equipment, Subcommittee SC 6, Air compressors and compressed air systems.
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ISO/TR 12942:2012(E)
Introduction
Classification and terminology standards are fundamental to the identification of a product for using in
industrial and trade communications, education, information search, data processing, research, development,
inventing, patenting, etc. It is intended that these standards be based on the latest technical achievements
and classification theories, cover all viable modern equipment design types, exclude ambiguity, be adapted to
easy translations into different languages by exact terms, and be flexible and open to new innovations. This
Technical Report is intended to contribute essentially to obtaining these aims for a possible subsequent
revision of ISO 5390.
The main modern problems in compressor classification and terminology are associated with rapid
development and implementation of new design types. In addition, many manufacturers include in a single
non-separable compressor package, not only an aftercooler, but also a receiver, dryer, etc. In these
conditions, it is important to establish and maintain unified patterns and principles for forming new derivative
and composed terms by using a few basic original terms as well as using, as far as possible, established
professional terms which have emerged spontaneously.
The problems related to the classification of compressor equipment are complicated by the wide spectrum and
diversity of application fields, resulting in a great number of applicability and performance criteria, such as:
⎯ compression principles;
⎯ basic design features;
⎯ energy forms used (electricity, fuel heat, etc.) and driver types;
⎯ cooling agents (air, water, etc.) and methods;
⎯ lubrication conditions (oil-free or contaminated with oil);
⎯ mobility, transportability;
⎯ prefabrication level (packaged and factory-assembled compressor, compressor plant, etc.);
⎯ operation modes and service parameters;
⎯ range of functions (compression, energy conversion, cooling, drying, etc.) and appropriate structural
composition of the equipment.
Neither identification of the compressor equipment and its application fields nor selection of compressors for
specific services and comparison of their technical and economical parameters are possible without
knowledge of this information. That is why it is intended that the attributes listed in this Technical Report serve
as a basis for the practical multi-dimensional classification system of compressor equipment.
Some explanatory notes and methodical approaches are presented in Annex A.

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TECHNICAL REPORT ISO/TR 12942:2012(E)

Compressors — Classification — Complementary information
to ISO 5390
1 Scope
This Technical Report gives a classification of modern compressor types and their definitions.
This Technical Report presents terms for use in technical and contractual specifications, manufacturer’s
literature, information searches and data processing systems, patent information, educational publications for
students, service and maintenance instructions, industrial statistics and market surveys, as well as in design,
quality, safety, testing and other standards, norms, regulations and codes.
It is intended that adequate technical and economical comparison and evaluation of compressor alternatives
for specific application conditions be performed with identical functional, mobility, service pressures and
service media classes, as well as with equal capacity ratings.
2 Design classes
2.1 General
The general hierarchy of compressor design classes is given in Figure 1.
Design classes specify the basic working principles and conceptual engineering philosophy of modern
compressors being operated, marketed, manufactured, developed, investigated or invented. The classification
tables in 2.2 to 2.5 contain preferred terms of basic compressor classes, their definitions and graphical
illustrations. Graphical materials are presented only as examples. Non-preferred synonyms are given in
parentheses. Special definitions are not given for those subclasses where the wording of the terms
characterizes sufficiently basic design features and attributes of the compressor types. More general high-
level terms can be used in the technical documentation instead of low-level particular subclasses, such as
“compressor”, “compressor plant” and “compressor equipment” after the first full description of functional and
design subclasses, and in all those cases where there is no possibility of confusion with other subclasses or
there is no need to differentiate between specific subclasses.

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ISO/TR 12942:2012(E)

Figure 1 — Design classes of compressors
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ISO/TR 12942:2012(E)
2.2 Classification by equipment type
Class, Subclass and definition Illustration
term (example only)
Compressor A machine or apparatus converting different types of energy into the
(generic term) potential energy of gas pressure for displacement and compression of
gaseous media to any higher pressure values above atmospheric pressure
with pressure-increase ratios exceeding 1,1.
NOTE 1 Similar equipment with pressure-increase ratio values of up to 1,1 is
regarded as ventilator.

Compressor A compressor in which conversion of different types of See 2.3 to 2.5 for specific
machine energy into the potential energy of gas pressure is effected classes
by mechanical motions of solid working members.
NOTE 2 In some design types of compressor machine,
intermediate liquid service media can be used for driving-force
transmitting from one solid member to the other one (e.g. in
electrically/hydraulically driven piston and diaphragm compressor).
Compressor A compressor in which conversion of different types of See 2.3 to 2.5 for specific
apparatus energy into the potential energy of gas pressure is effected classes
by stationary positions of working members effecting basic
energy conversion functions, mechanical motions being
used only for auxiliary functions, such as gas inlet and
outlet, and energy-agent supply and withdrawal.
2.3 Classification of compressor apparatuses by operation principles
Class, Subclass Definition Illustration
term (example only)
Compressor Ejector A compressor apparatus of dynamic type, comprising
apparatus suction chamber, cylindrical throat and diffuser, in which
auxiliary
the gas-pressure increase is obtained in continuous flow
fluid
by initial increasing its kinetic energy by mechanical action
of the motive high-velocity auxiliary fluid stream entraining

the gas into the accelerating mixed stream, and
successive conversion of the kinetic energy into the

potential energy of the mixture pressure by deceleration of
the mixture flow in the diffuser, the high velocity of the
gas
motive auxiliary-fluid steam being created by its
expansion in the nozzle from pressurized state to the
initial or lower pressure of the gas being compressed.
Thermo- A compressor apparatus of displacement type in which
compressor the gas pressure increase, its discharge and gas intake
are obtained by cyclically heating and cooling of the

closed volumes of the gas.
Adsorption A compressor apparatus of displacement type in which
compressor the gas pressure increase, its discharge and gas intake
are obtained by cyclical adsorption of the gas by special
adsorbents such as metal hydrides and its desorption at

higher pressures by changing temperature conditions.

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ISO/TR 12942:2012(E)
Class, Subclass Definition Illustration
term (example only)
Compressor Acoustical A compressor apparatus of displacement type in which
apparatus compressor the gas pressure increase, its discharge and gas intake
Acoustical generator
(continued) are obtained by cyclical formation of low- and high-
pressure phases in the closed volumes of the gas due to

actions of pressure waves emitted by an acoustical
generator

Pressure – A compressor apparatus of displacement type in which
Fixed end plates
shock the compression of successive volumes of the gas is
compressor effected by shock waves created by the second high-
(Pressure pressure energy-carrying gas in several longitudinal
exchanger) through channels arranged circumferentially on the
cylindrical drum, these channels being cyclically closed by
rotation of the drum between fixed end plates having
inlet/outlet ports and blind zones, the shock waves being
generated by cyclical exposure of channel ends to the
energy-carrying-gas manifold, and inlet/outlet of both Rotating drum

fluids being achieved by synchronization of drum-rotating
speed in respect to the fixed inlet/outlet ports with the
velocity of pressure-wave propagation.


NOTE 1  The rotating drum is not imparting any energy to the
gas to be compressed. Its rotation synchronized with shock wave
velocity is an auxiliary movement only ensuring control of fluid
flows. The drum can be driven by an small auxiliary prime mover
or any other power transmitting shaft.
NOTE 2  The shock-wave propagation from one channel end to
another one and gas compression up to pressure equalization of
two fluids in the channels occur essentially faster than mixing of
fluids.

Liquid-column A compressor apparatus of displacement type in which
compressor admission and compression of successive volumes of the
gas are performed periodically by forced expansion and
diminution of a closed space(s) in the vertical casing of
any form due to displacement of the auxiliary-liquid
column in said casing.
NOTE 1 The displacement of the auxiliary-liquid column can
be generated by external renewable natural-energy sources,
e.g. water waves.

NOTE 2 The liquid-displacement source subclasses are:
⎯ sea-wave driven compressors;
⎯ tidal-wave driven compressors.

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ISO/TR 12942:2012(E)
2.4 Classification of compressor machines by operation principles
Class, Subclass Definition Illustration
term (example only)
Compressor Dynamic compressor, A compressor machine in which the gas pressure
machine turbocompressor increase is achieved in continuous flow essentially
by increasing its kinetic energy in the flow path of
the machine due to acceleration to the high
velocities by mechanical action of blades placed on
a rapid rotating wheel and further transformation of
the kinetic energy into the potential energy of the

elevated pressure by successive deceleration of
the said flow.
Positive-displacement A compressor machine in which the admission and
compressor compression of successive volumes of the
gaseous medium are performed periodically by
forced expansion and diminution of a closed
space(s) in a working chambers(s) by means of
displacement of a moving member(s) or by
displacement and forced discharge of the gaseous
medium into the high-pressure area.
NOTE The closed spaces with variable or

displaceable volumes represent compression chambers.
In one working chamber, there can be one or several
variable-volume compression chambers.
Combined A compressor machine in which the compression Simultaneous compression
compressor machine of gaseous medium or media is performed
      driver   gear
simultaneously or successively by dynamic and
positive-displacement compressors driven by a
common prime mover.

Successive compression
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ISO/TR 12942:2012(E)
2.5 Design classes of compressor machines
2.5.1 Design classes of turbo compressors (dynamic compressors)
Class, Subclass Definition Illustration
term (example only)
Turbo Radial turbo- A turbo compressor in which the acceleration of the gas

compressor compressor stream in the meridional plane is performed in radial
(Radial-flow direction with respect to the axis of rotation of the bladed
turbo- wheel.
compressor)
NOTE 1 The subclasses of radial compressors are:
⎯ radial centrifugal compressor;
⎯ radial centripetal compressor.
NOTE 2 The broader term “radial compressor” can be used
instead of “centrifugal compressor” if there is no possibility of
confusion with centripetal radial compressors.
Centrifugal A radial turbo compressor in which the
compressor acceleration of the gas stream is caused
essentially by centrifugal forces and
performed from the centre of the rotating
wheel to its periphery.
NOTE 3 The basic specific subclasses of
the centrifugal compressors are:
a) flow-number classes of the rotating wheel:
1) single-flow compressor;
2) double-flow compressor;
b) casing-design classes:
1) horizontally split compressor;
2) vertically split compressor with solid
casing;
3) vertically split compressor with
stacked casing;
c) cooling-configuration classes:
1) non-cooled compressor;
2) isothermal (after-stage-cooled
compressor):
a) with built-in coolers;
b) with separate coolers;
3) stage-group-cooled (sectionally
cooled) compressor;
4) after-casing cooled compressor;

5) water-injection-cooled compressor;
d) shaft-number classes:
1) single-shaft compressor;
2) multi-shaft compressor.
NOTE 4 Gas cooling system is a
component part of the aggregated compressor
equipment (compressor plant); however, in
spite of this gas cooling methods influence also
essentially the design of the compression
mechanism (mechanical compressor).

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ISO/TR 12942:2012(E)
Class, Subclass Definition
Illustration
term
(example only)
Turbo Radial turbo- Centripetal A radial turbo compressor in which the
compressor compressor compressor gas stream is accelerated essentially by
(continued) (Radial-flow centripetal forces induced by mechanical
turbo- action of blades placed circumpherentially
compressor) on the rotating wheel and moves from its
periphery to the centre.
(continued)

Axial A turbo compressor in which the acceleration of the gas
compressor stream in the meridional plane is performed in the
(axial-flow direction parallel to the axis of rotation of the bladed
compressor) wheel.
NOTE 5 The basic design subclasses of axial compressor are:
⎯ compressors with fixed stator blading;

⎯ compressor with variable stator blading.
Peripheral A turbo compressor in which the acceleration of the gas
flow stream is performed by its composed resulting motion in
compressor peripheral (circumferential) direction in respect of the axis
(periflow of rotation of the bladed wheel.
compressor,
NOTE 6 The resulting peripheral motion with helical screw-
vortex
type flow pattern of the gaseous medium is composed of the
compressor,
radial motion in the rotor pockets under the centrifugal forces, the
regenerative
circulatory motion in the ring-shaped peripheral stator channel
compressor,
caused by centrifugal pressure gradient superimposed by the
drag circumferential motion induced by rotation of the wheel.

compressor,
NOTE 7 The basic subclasses of peripheral-flow
tangential
compressors according to configuration and location of bladed
compressor)
rotor channels are:

a) side-channel 1. single-side-
Individual definitions
compressor channel
are not necessary
compressor
because the
wording of the terms
2. multi-side-
characterizes
channel


compressor sufficiently basic
design features of
b) peripheral- 1. single-
the subclasses.
channel peripheral
compressor channel
compressor
2. multi-peripheral


channel
compressor
c) angle-channel compressor


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ISO/TR 12942:2012(E)
Class, Subclass Definition
Illustration
term
(example only)
d) double-angle-channel compressor
Turbo Peripheral
compressor flow
(continued) compressor
(periflow

compressor,
vortex
e) stepped-channel compressor
compressor,
regenerative
compressor,
drag
compressor,
tangential

compressor)
(continued)
Diagonal-flow
A turbo compressor in which the acceleration of the gas
compressor
stream in the meridional plane is performed at acute
(mixed-flow
angles between axial and radial directions to the axis of
compressor)
rotation of the bladed wheel.

Cross-flow A turbo compressor in which the acceleration of the gas
compressor stream is performed in diametrical, cross-direction with
(transverse- respect to the axis of rotation of the bladed wheel thus
flow action of two blade rows on the stream is achieved.
compressor,
NOTE 8 Fixed deflectors can be used inside the bladed
diametrical
wheel for better flow guidance between two rows of blades.
compressor)

Combined A turbo compressor in which the compression of gaseous
turbo- medium or media is performed simultaneously or
compressor successively in different types of turbo compressors
driven by a common prime mover.
NOTE 9 Subclasses of combined turbo compressors can be:
⎯ axial-radial turbo compressor;

⎯ diagonal-radial turbo compressor;
⎯ radial-peripheral turbo compressor, etc.




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ISO/TR 12942:2012(E)
2.5.2 Design classes of positive displacement compressors
2.5.2.1 General
Class, Subclass Definition Illustration
term (example only)
Positive Rotary A displacement compressor in which gas
displacement compressor admission and diminution of its successive
compressor volumes or its forced discharge are performed
cyclically by rotation of one or several rotors in a
compressor casing.
NOTE 1 The rotor-number subclass are:
⎯ Single-rotor compressor,

⎯ Double-rotor compressor,
⎯ Multi-rotor compressor.
A displacement compressor in which gas admission and
Reciprocating
diminution of its successive volumes are performed
compressor
cyclically by straight-line alternating movement of a moving
member(s) in a compression chamber(s).
NOTE 2 Design subclasses of reciprocating
compressors are:
⎯ piston compressor;

⎯ diaphragm compressor;
⎯ bellows-type compressor.
Peristaltic A displacement compressor in which admission of
compressor the gas volumes and their forced discharge are
performed cyclically by local squeezing of sections
of a flexible pipe rested on arc-shaped support by
rollers of an external rotor and by displacing the
trapped gas volumes from low-pressure side to
high-pressure area.
NOTE 3 The inner flexible-pipe surface driven by the
rollers represents the working member in the peristaltic

compressors.

Orbital A displacement compressor in which gas
compressor admission and diminution of their successive
volumes are performed cyclically by plain-parallel
non-rotating orbital motion of the working member
along the circular or other closed-curve path in the
working chamber.
Subclass: scroll compressor
Scroll An orbital compressor in which

compressor closed-space compression
chambers are formed between two
identical spiral bands inserted
eccentrically in each other and their
flat end cover plates, the volumes
of said spaces being cyclically
decreased and increased from
periphery to the centre by orbital
non-rotating plane-parallel motion
of one spiral band inside the fixed

one along the circular path.
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ISO/TR 12942:2012(E)
Class, Subclass Definition Illustration
term (example only)
Positive Swing-lobe A displacement compressor in which gas
displacement compressor admission and diminution of its successive
compressor (oscillating- volumes are performed by angular swinging
(continued) lobe (rocking) motion of one or several lobes around
compressor) their axes in an cylindrical or partly cylindrical
casing.



Combined A positive displacement compressor in which the
positive- compression of gaseous medium or media is
displacement performed simultaneously or successively in
compressor different types of positive displacement
compressors driven by a common prime mover.
2.5.2.2 Design classes of single-rotor compressors
Class, Subclass Definition Illustration
term (example only)
Single-rotor Multi-segment A single-rotor compressor in which the compressor
compressor compressor chambers constitute circle segments in cross-section,
their expansion and diminution being obtained by passing
through the variable-height crescent-shaped space
between the inner surface of the casing and eccentrically
mounted rotor of the smaller diameter.

NOTE 1 The design subclasses of multi-segment
compressors are:
⎯ liquid-ring compressor;
⎯ sliding-vane compressor;
⎯ swing-vane compressor.
Liquid-ring A multi-segment compressor in which
compressor segment- shaped compression chambers
are formed between the radial or forward-
curved vanes of the eccentric rotor and

rotating liquid layer created and
maintained by rotating vanes and pressed
concentrically to the inner surface of the
casing by centrifugal forces.

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ISO/TR 12942:2012(E)
Class, Subclass Definition Illustration
term (example only)
Single-rotor Multi-segment Liquid-ring
compressor compressor compressor

(continued) (continued) (continued)
Single-acting compressor




Double-acting compressor (with two
crescent-shaped spaced in the oval-type
casing)

Sliding-vane A multi-segment compressor in which
compressor segment-shaped compression chambers
are formed between the inner surface of
the cylindrical casing and flat solid vanes
sliding in radial or cord-shaped slots of
the eccentric rotor and being constantly
pressed to said surface by centrifugal
forces.
NOTE 2 The design subclasses are:
⎯ single-acting compressor;
⎯ double-acting compressor.

Swinging-vane A multi-segment compressor in which
compressor segment-shaped compression chambers
are formed between the inner surface of
the cylindrical casing and curvilinear
flexible or solid vanes rigidly connected or
correspondingly pivoted by one of their
ends to the rotor and being constantly
pressed to the casing surface by
centrifugal forces.
NOTE 3 The design subclasses are:

⎯ single-acting compressor;
⎯ double-acting compressor.
Rolling-rotor A single-rotor compressor in which the expansion and
compressor diminution of variable-volume compression chambers are
performed by rolling of the eccentric rotor along the inner
surface of the casing of the larger size, the axis of the
rotor being circulating by its rotation around the casing
axis.

NOTE 4 The rotor-profile subclasses are:
⎯ cylindrical-rolling-rotor compressor;
⎯ trochoidal- rolling-rotor compressor;
⎯ special profile rolling -rotor compressor.

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ISO/TR 12942:2012(E)
Class, Subclass Definition
Illustration
term
(example only)
Single-rotor Rolling-rotor Cylindrical- A rolling-rotor compressor in which the
compressor compressor rolling-rotor rotor and casing are accomplished by
(continued) (continued) compressor cylindrical profiles, low- and high-
pressure areas
...