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High Quality Compressed Air
from Generation to Application
A Guide to ISO 8573.1:2001
Air Quality Classes
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domnick hunter is an international group of companies specialising in the high quality filtration, separation and
purification of compressed air, gases and liquids.
domnick hunter has over 40 years of experience in the purification industry and has been instrumental in the
development of both the international standards for compressed air and the standards for filter testing. domnick
hunter continues to work closely on new standards with such governing bodies as British Compressed Air Society
(BCAS) the International Standards Organisation (ISO), PNEUROP and the Compressed Air and Gas Institute (CAGI).
This document provides an introduction to ISO 8573.1 the international standard for compressed air quality,
purification equipment required to achieve the standards and how to apply the standard to typical applications. |
ISO 8573 – The compressed air quality standard
ISO8573 is the group of international standards relating to the
quality of compressed air. The standard is made up of nine
separate parts, part 1 specifying the quality requirements
of the compressed air and parts 2 – 9 specifying the methods
of testing for a range of contaminants.
In 2001, the ISO 8573.1 air quality standard was amended in
an effort to provide a more stringent air quality specifications
for critical applications and the latest revision is expressed
as ISO8573.1 : 2001.
Within ISO8573.1 : 2001, a number of quality classes are
shown in tabular form, each specifying the maximum amount
of solid particulate, water and oil allowable per cubic metre
of compressed air. | Solid Particulate
The changes introduced to ISO 8573.1 in 2001 were
specific to particulate contamination, however the
significant improvements in particulate cleanliness are
not always apparent when comparing the tables from
the 1991 and 2001 editions. | | class | solid particulate maximum number of particles per m3 | water pressure dewpoint °c | oil (incl. vapour) mg/m3 | | 0.1-0.5micron | 0.5-1 micron | 1.0-5micron | | 1 | 100 | 1 | 0 | -70 | 0.01 | | 2 | 100,000 | 1,000 | 10 | -40 | 0.1 | | 3 | - | 10,000 | 500 | -20 | 1 | | 4 | - | - | 1,000 | 3 | 5 | | 5 | - | - | 20,000 | 7 | - | | 6 | - | - | - | 10 | - | |
Extract from ISO 8573 : 1991 Part 1 for particulate (previous standard)
| quality class | dirt particle size in micron | concentration mg/m3 | | 1 | 0.1 | 0.1 | | 2 | 1 | 1 | | 3 | 5 | 5 | | 4 | 15 | not specified |
Extract from ISO 8573 : 2001 Part 1 for particulate (latest standard) | class | solid particle maximum number of particles per m3 | | 0.1-0.5micron | 0.5-1 micron | 1.0-5micron | | 1 | 100 | 1 | 0 | | 2 | 100,000 | 1,000 | 10 | | 3 | - | 10,000 | 500 | | 4 | - | - | 1,000 | | 5 | - | - | 20,000 | | 6 | - | - | - | |
Using the classes, a maximum level can be specified for
each contaminant which is expressed as
ISO 8573.1 : 2001 Class Solid Particulate - Water - Oil
For example
ISO 8573.1 : 2001 Class 1.2.1
Which equates to
100 Solid Particles 0.1-0.5 micron/m3
1 Solid Particle 0.5 - 1 micron/m3
0 Solid Particles 1 - 5 micron/m3
Water Vapour Pressure Dewpoint -40°C
Oil aerosol and vapour 0.01 mg/m3 |
As can be seen above, the two editions of the standard
do not present particle contamination requirements in
the same way.
The table from the 1991 edition shows a maximum size
rating for the solid particulate and a concentration
whilst the 2001 edition shows both a size rating for the
particulate and the maximum number of particles
allowed per cubic metre. To show the differences
between the two tables and highlight the improved air
quality requirements, the concentration levels shown in
the 1991 edition must be converted into a quantity of
particles. | | |
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Using this method, shows that class 1 from the 1991
edition permitted a maximum of 191 billion particles per
cubic metre, whereas the 2001 edition only allows 101.
The table below highlights exactly how much cleaner the
2001 edition is.
| quality class | 2001 EDITION X TIMES CLEANER THAN 1991 EDITION | | 1 | 1.9 billion times cleaner than 1991 Class 1 | | 2 | 19 thousand times cleaner than 1991 Class 2 | | 3 | 7 thousand times cleaner than 1991 Class 3 | | 4 | - |
When specifying purification equipment, consideration should
be given to the requirements of the user. It should not be
assumed that an application that previously required particulate
removal to class 1 still requires this level today.
Wet particulates are removed using a coalescing type filter which
provide the additional function of removing oil / water aerosols.
Dry particulate filters are also available and are typically used
after adsorption dryers or at the point of use. The test methods
for measuring solid particles are covered in ISO 8573.4 |  |
Water
The values for water refer to water vapour and are expressed
as pressure dewpoints in degree’s Celsius. Water vapour is
removed using a dryer, of which there are various types
available. Of the six dewpoint levels shown in the quality
classes, the first three are typical of dewpoints achieved by
adsorption dryers and the last three are those achieved by
refrigeration dryers. The test methods for the measurement
of pressure dewpoint are covered in ISO 8573.3
Oil
The ISO8573.1:2001 table shows the recommended maximum
levels for oil including vapour. Oil aerosols can be removed by
using a coalescing type filter, whilst oil vapour must be
removed using an adsorption type filter. Removal of aerosol &
vapour will require the use of both filter types. The total value
for oil in a system is a combination of test results from both
ISO8573.2 & ISO8573.5. |  |
Micro-organisms
Many applications within the food and pharmaceutical
industries require air which is free from micro-organisms such
as bacteria, viruses, yeast and fungi. ISO8573.1 considers these
as solid contaminants and is limited to identifying systems as
either sterile or non-sterile. The test methods for measuring
micro-organisms are covered in ISO 8573.7
Air quality & energy efficiency
Choosing purification equipment for today’s modern
production facilities that can deliver the right balance of air
quality and low cost of ownership can be a daunting task.
At domnick hunter, uncompromising performance and energy
efficiency are paramount and in these energy conscious days,
selecting domnick hunter purification equipment not only
means that you get air quality to international standards but
also ensures operating costs are kept to a minimum. |  |
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BULK LIQUID REMOVAL
GRADE WS
High Efficiency Water Separators
WS water separators employ centrifugal and impingement
separation techniques for the removal of up to 99% of bulk
liquid contamination.
DEPTH FILTRATION (COALESCING
& DRY PARTICULATE FILTER)
Depth filters generally constitute a fibrous material made into flat sheets of randomly distributed formed nanofibres. Depth filters rely on the density and thickness of the fibre layers to trap the particulate.
Removal of the particulate occurs both on the surface and within the depth of the media. The size of the particle that can be captured has finite limits dictated by the diameter of the fibres used in the media construction and the degree of free space between the fibres. By using this method of filtration, large quantities of particulate can be captured before blockage occurs.
Nanofibre filter media
GRADE AO
High Efficiency General Purpose Protection Particle removal down to 1 micron, including water and oil aerosols. Maximum remaining oil aerosol content : 0.6 mg/m3 at 21°C / 0.5 ppm(w) at 70°F.
GRADE AA High Efficiency Oil Removal Filtration
GRADE AR
General Purpose Dust Filtration
Dry particle removal down to 1 micron
GRADE AAR
High Efficiency Dust Filtration
Dry particle removal down to 0.01 micron.
| HIGH FLOW BIO-X Sterile Air / Particulate Free
Full retention of bacteria, viruses and particulate.
Based on depth filter technology. Retention correlated to an aerosol bacterial and viral challenge.
EMBMRANE FILTRATION
Microporous membrane filters remove contaminants by a combination of mechanisms. Larger particles and microorganisms are retained by size exclusion / sieve captured on the membrane surface. Smaller bacteria and viruses (as small as 0.02 micron) are fully retained within the depth of the membrane, and significant retention takes place at even smaller sizes. Membranes used for air filtration do not have such a defined pore structure as those associated with liquid applications. They have a structure that is similar to that of a depth media apart
from the pores being significantly smaller in size.
 
Air Membrane Liquid Membrane
HIGH FLOW TETPOR MEMBRANE FILTERS Sterile Air / Particulate Free
Full retention of bacteria, viruses and particulate.
Based on membrane technology. Retention correlated to a liquid bacterial challenge (ASTM 838-38) as well as bacterial and viral aerosol challenge. Used for the most critical of applications including medical, pharmaceutical / aseptic packaging and electronics.
 
OIL-X EVOLUTION Depth filters High Flow BIO-X Depth Filters
High Flow TETPOR Membrane Filters
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ADSORPTION FILTRATION
Adsorption filter elements are made up of various materials in granular form arranged in a deep bed. This filtration technique relies on contact or dwell time between the air and the adsorption media. It is during this time that vapour molecules are attracted to and held on the surface area of the media.
Activated carbon is employed for oil vapour removal using this technique with its high affinity for oil vapour and its extremely high surface area, created by its porous structure. A handfull of activated carbon has a surface area larger than a football field.
Adsorption elements have a limited life, which is affected by many factors, principally temperature and relative humidity.
Activated carbon
GRADE ACS, AC & OVR Oil Vapour & Odour Removal
(Precede Grade ACS, AC and OVR with Grade AA filter) Maximum remaining oil vapour content : 0.003 mg/m3 at 21°C / 0.003 ppm(w) at 70°F.
REFRIGERATION DRYING
A refrigeration dryer extracts water vapour by the application of cooling and subsequent condensation. Condensation of water vapour occurs on internal cooling surfaces and is then separated and drained. Refrigeration dryers are designed to deliver pressure dewpoints above 0°C to prevent freezing on the internal cooling surfaces. Air is reheated before it re-enters the system to prevent piping from ‘sweating’ in humid conditions.
Refrigeration Dryers
CRD Refrigeration Dryers Delivering Pressure Dewpoints of 3°C (37°F) & 10°C (50°F).
 
OVR 6000 hour Oil Vapour Removal CRD Refrigeration Dryers | ADSORPTION DRYING
An adsorption dryer extracts water vapour from the compressed air by attraction and adhesion of molecules in a gaseous or liquid phase to the surface of an adsorbent material. The adsorbent can often be regenerated by removing the adsorbed water. Although the principle of water removal is common, various methods of regenerating the adsorption bed are available and include heatless regeneration (Pressure Swing Adsorption), heat regenerative (Thermal Swing Adsorption), vacuum regeneration and blower regeneration.
Adsorbent Desiccant Bead
High Efficiency Adsorption Dryers
Delivering Pressure Dewpoints of -70°C (-100°F) / -40°C (-40°F) / -20°C (-4°F)
A full range of PSA, TSA, Vacuum & Blower regeneration adsorption dryers are available from domnick hunter for compressor room and point of use applications.
Adsorption dryers are selected to match not only air quality requirements, but also capital and operational cost targets of the user. Dryer types include:
PNEUDRI - Modular PSA / TSA Regeneration
Classic - Twin Tower PSA / TSA & Blower Regeneration DTV - Vacuum Regeneration
 
PNEUDRI Modular Adsorption Dryers DTV and Classic Twin Tower Adsorption Dryers
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High quality compressed air from generation to application
The quality of air required throughout a typical compressed air system can vary. The extensive range of purification equipment available from domnick hunter is ideal for both centralised and decentralised compressed air systems. This allows the user to tailor the quality of air for each specific application, from general purpose ring main protection, through to critical clean dry air (CDA) point of use systems. domnick hunter can tailor its range of purification equipment to exactly match system requirements, ensuring both capital and operational costs are kept to a minimum.
To achieve the levels of cleanliness specified by ISO 8573.1 2001 a careful approach to system design, commissioning and operation must be employed.
It is highly recommended that the compressed air is treated prior to entry into the distribution system as well as at each usage point or application.
This approach to system design provides the most cost effective solution to system purification as it not only removes the contamination already in the distribution system, it ensures that only the most critical area’s receive air treated to the highest level.
The typical system layout drawings included in this document show installations with purification equipment in the compressor room to protect the distribution system and also at the point of application.
In many instances the compressed air system will be supplying air to more than one application and although the purification equipment specified in the compressor room would remain unchanged, the point of use protection will vary depending upon the air quality requirements of each application.
For example, air used for the pneumatic conveying of food stuffs or ingredients will require the highest level of purification, whilst the air used to operate the pneumatics on the production machinery may only require general purpose protection.
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Product Selection
| class | solid particulate maximum number of particles per m3 | water pressure dewpoint °c | oil (incl. vapour) mg/m3 | | 0.1-0.5micron | 0.5-1 micron | 1.0-5micron | | 1 | 100 | 1 | 0 | -70 | 0.01 | | 2 | 100,000 | 1,000 | 10 | -40 | 0.1 | | 3 | - | 10,000 | 500 | -20 | 1 | | 4 | - | - | 1,000 | 3 | 5 | | 5 | - | - | 20,000 | 7 | - | | 6 | - | - | - | 10 | - |
Solid Particulate
CLASS FILTRATION GRADES
Class 1 High Flow BIO-X / High Flow TETPOR (Requires pre-filtration)
Class 2 AO + AA (AR+AAR for dry particulate)
Class 3 AO (AR for dry particulate)
Water
CLASS DRYER
Class 1 PNEUDRI / Classic / DTV Sized for –70°C PDP
Class 2 PNEUDRI / Classic / DTV Sized for –40°C PDP
Class 3 PNEUDRI / Classic / DTV Sized for –20°C PDP
Class 4 CRD Refrigeration Dryer Sized for +3°C PDP
Class 5 CRD Refrigeration Dryer Sized for +3°C PDP
Class 6 CRD Refrigeration Dryer Sized for +10°C PDP
Oil
CLASS FILTRATION GRADES
Class 1 AO + AA
+ OVR, AC or ACS if the maximum inlet oil vapour
concentration exceeds 0.005mg/m3
Class 2 AO + AA
Class 3 AO
Class 4 AO
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HIGH QUALITY OIL FREE AIR - Air Quality to ISO 8573.1: 2001 : Class 2.1.1, Class 2.2.1, Class 2.3.1 at application
Bulk contamination is removed to an adequate level prior to the air entering the distribution system.
Point of use particulate filter(s) are used for removal of contamination within the distribution system.
*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal filter will be required.
| Typical Applications
General ring main protection
Pre-filtration to point of use adsorption air dryers
Plant automation
Air Logistics
Pneumatic tools
General instrumentation
Air conveying
| Air motors
Temperature control systems
Blow guns
Gauging Equipment
Raw material mixing
Sand / bead blasting
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CRITICAL APPLICATIONS - Air Quality to ISO 8573.1: 2001 Class 1.1.1, Class 1.2.1, Class 1.3.1 at application
Bulk contamination is removed to an adequate level prior to the air entering the distribution system.
Point of use oil vapour removal and sterile air filtration (membrane or depth) installed for critical application at point of use.
Only air for the critical application should be treated to the highest level. For non-critical applications fed by the same distribution system, high efficiency point of use filtration should be installed.
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| Typical Applications
Pharmaceutical products
Silicon wafer manufacturing
TFT / LCD Screen manufacturing
Memory device manufacturing
Optical storage devices (CD, CDRW, DVD, DVDRW)
Optical disk manufacturing (CD’s/DVD’s):
| Hard disk manufacturing
Foodstuffs
Dairies
Breweries
CDA systems for electronics manufacturing
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HIGH QUALITY OIL FREE AIR - Air Quality to ISO 8573.1: 2001 : Class 2.1.1, Class 2.2.1, Class 2.3.1 at application Bulk contamination is removed to an adequate level prior to the air entering the distribution system. Point of use particulate filter(s) are used for removal of contamination within the distribution system.
*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal filter will be required.
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| Typical Applications
Typical Applications
General ring main protection
Pre-filtration to point of use adsorption air dryers
Plant automation
Air Logistics
Pneumatic tools
General instrumentation
Air conveying
| Air motors
Temperature control systems
Blow guns
Gauging Equipment
Raw material mixing
Sand / bead blasting
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GENERAL PURPOSE OIL-FREE AIR - Air Quality to ISO 8573.1: 2001 Class 3.-.2, Class 2.-.1.(water vapour removal not specified) Bulk contamination is removed to an adequate level prior to the distribution system.*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal stagewill be required.
The requirements for breathable quality air are not covered in ISO 8573.1:2001. Refer to breathing air standards for thecountry of installation.
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| Typical Applications
Typical Applications (Water Vapour Removal Not Specified)
General ring main protection
Metal stamping
Forging
General industrial assembly (no external pipework)
Pre-filtration to point of use breathing air systems
Workshop
Garage
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System Recommendations
To achieve the levels of cleanliness specified by ISO 8573.1:2001 a careful approach to system design, commissioning and operation must be employed.
It is recommended that the compressed air is treated prior to entry into the distribution system and also at critical usage points / applications.
This ensures that contamination already in the distribution system is removed. Installation of compressed air dryers to a previously wet system could result in additional dirt loading for point of use filters for a period whilst the distribution system dries out. Filter elements may need to be changed more frequently during this period.
For installations where oil-free compressors are used, both general purpose Grade AO and high efficiency Grade AA should be used. The general purpose filter must be installed to protect the high efficiency filter from bulk water aerosols and solid particulate.
Install purification equipment at the lowest temperature above freezing point downstream of aftercoolers and air receivers. This allows a greater amount of oil and or water vapour to condense out for removal by water separators & coalescing filters prior to a dryer.
Point of use purification equipment should be installed as close to the application as possible. This ensures that the maximum amount of rust and pipe scale is removed prior to the application.
Purification equipment should not be installed downstream of quick opening valves and should be protected from possible reverse flow or other shock conditions.
Purge all piping leading to the purification equipment before installation and all piping after the purification equipment is installed and before connection to the final application.
If by-pass lines are fitted around purification equipment, ensure adequate filtration is fitted to the by-pass line to prevent contamination of the system downstream.
Provide a facility to drain away collected liquids from the purification equipment. Collected liquids should be treated and disposed of in a responsible manner.
In critical applications, membrane filters should be used at point of use to ensure no particulate is carried over to the application.
The lifetime of oil vapour removal filter elements is affected by the inlet oil concentration, relative humidity and temperature of the compressed air. For critical applications or systems where frequent element changes are not possible, domnick hunter OVR oil vapour removal systems should be installed.
| The piping used downstream of membrane filters should be electropolished stainless steel and be crevice free at all joints. Clean down time for a newly commissioned system will depend upon the surface area of the system, the system flow rate and the initial cleanliness of the piping and fittings. Clean down can be achieved by high flow clean air purging for extended periods of time during which all air should be purged to atmosphere.
Sterile Air
If running an aseptic process (i.e. free from microbiological contamination) it is essential that a sterile filter is installed at the point of use. This may either be based on glass nanofibre depth media or membrane.
Sterility can only be guaranteed and maintained if the filter and associated downstream process equipment are sterilised and maintained in accordance with manufacturers instructions. This is normally achieved using steam sterilisation but chemical sterilisation techniques such as vapour hydrogen peroxide can also be used.
It is recommended that sterile filters are tested for efficiency on a regular basis.
Maintaining System Efficiency
Regular service is essential to maintaining system performance.
To maintain your guaranteed compressed air quality, purification equipment must be maintained annually with genuine domnick hunter parts. Failure to maintain your purification equipment will invalidate performance guarantees and could result in reduced production performance, degrading air quality and increased running costs.
Preventative maintenance provides you with the following benefits:
• Lowest running costs
• Guaranteed compressed air quality
• Continued protection of downstream equipment and processes
• Peace of mind< br> After sales care package
For peace of mind, domnick hunter can manage your compressed air quality and guarantee future performance with a world-wide aftersales care package. Further details can be found on www.servicereminder.com
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