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ISO Standardization
International Standard ISO8573-1 has become the industry standard method
for specifying compressed air cleanliness.
ISO8573-1:2010
CLASS
Solid Particulate Water Oil
Maximum number of particles per m
3
Mass
Concentration
mg/m
3
Vapor
Pressure
Dewpoint
Liquid
g/m
3
Total Oil (aerosol liquid and
vapor)
mg/m
3
0.1 - 0.5 micron 0.5 - 1 micron
1 - 5 micron
0 As specified by the equipment user or supplier and more stringent than Class 1
1 ≤ 20,000 ≤ 400 ≤ 10 - ≤ -94°F (-70°C) - 0.01
2 ≤ 400,000 ≤ 6,000 ≤ 100 - ≤ -40°F (-40°C) - 0.1
3 - ≤ 90,000 ≤ 1,000 - ≤ -4°F (-20°C) - 1
4 - - ≤ 10,000 - ≤ 37.4°F (3°C) - 5
5 - - ≤ 100,000 - ≤ 44.6°F (7°C) - -
6 - - - ≤ 5 ≤ 50°F (10°C) - -
7 - - - 5 - 10 - ≤ 0.5 -
8 - - - - - 0.5 - 5 -
9 - - - - - 5 - 10 -
X - - - > 10 - > 10 > 5
Clean, energy efficient compressed air
is the goal
The key is finding the optimum balance of compressed air quality required,
and minimizing the cost and energy needed to achieve that quality.
ISO 8573-1:2010 is now the industry standard
for specifying compressed air cleanliness. In
this standard, three very common contaminants
are focused on, and the various classes describe
how clean and dry the compressed air must be in
order to achieve that classication. Solid particle
content by size range, water content by pressure
dewpoint, and oil (including oil vapor) content in
mg/m
3
is described for each of the classes from
Class 0, 1, 2, 3,…,9, and X. Class 0 is described as
being as specied by the equipment user and is
more stringent than Class 1. Even Class 1, because
of its -94 F (-70 C) pressure dewpoint, is rarely
required in general industrial settings. Most critical
compressed air applications will probably fall into
Class 2 described in the table below.
ISO 12500 establishes a uniform test procedure to
be used by all lter companies in the compressed
air industry. Using this test, air lters can be
tested to equate their performance to ISO 8573-
1:2010. is procedure species exactly how
the lters should be tested at either of two inlet
challenge levels: 10 mg/m
3
or 40 mg/m
3
. Since
high-eciency lters are often plumbed in series
or staged ltration, the prelters or precoalescers
are often rated at the 40 mg/m
3
level, and nal or
polishing coalescing lters are most often rated
at the 10 mg/m
3
level, since they are typically the
beneciary of preltration.
Using a high performance lter to
measure oil aerosol removal, these
eects can be observed:
Customary remaining oil content of compressors
30 ppm
12 ppm
< 6 ppm
Piston and mobile screw
compressors
Stationary screw compressors
Rotary vane compressors
Reference conditions 14.5 psi (a) (1 bar (a)), 68°F (20°C), 0 % relative humidity.
Particulate contamination in a compressed
air system can be drawn into the compressor
through its intake, or be generated through
the compression process or by other system
components themselves. Water enters the
system through the compressor’s intake as
humidity in the air. Once compressed the
air is saturated meaning that depending on
the environment of the system, the water is
present either in liquid or vapor state. Oil
and hydrocarbon vapors can be drawn into
the compressor intake as well, but the largest
contributor is carryover of compressor lubricant.
See the chart below for typical carryover levels by
compressor type.