ISO Standard for Compressed Air Dryer


Compressed Air Dryer Contaminants and Purity Classes

1. Scope
This part of ISO 8573 specifies purity classes of compressed air with respect to particles, water and oil, independent of the location in the compressed air system at which the air is specified or measured.
This part of ISO 8573 provides general information about contaminants in compressed air systems as well as links to the other parts of ISO 8573, either for the measurement of compressed air purity or the specification of
compressed air purity requirements.
In addition to the above-mentioned contaminants of particles, water and oil, this part of ISO 8573 also identifies gaseous and microbiological contaminants. Guidance is given in Annex A as to the application of this part of ISO 8573.

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 7183, Compressed-air dryers — Specification and testing
ISO 8573-2, Compressed air — Part 2: Test methods for oil aerosol content
ISO 8573-3, Compressed air — Part 3: Test methods for measurement of humidity
ISO 8573-4, Compressed air — Part 4: Test methods for solid particle content
ISO 8573-5, Compressed air — Part 5: Test methods for oil vapour and organic solvent content
ISO 8573-6, Compressed air — Part 6: Test methods for gaseous contaminant content
ISO 8573-7, Compressed air — Part 7: Test method for viable microbiological contaminant content
ISO 8573-8, Compressed air — Part 8: Test methods for solid particle content by mass concentration
ISO 8573-9, Compressed air — Part 9: Test methods for liquid water content

3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7183, ISO 8573-7 and the following apply.
suspension in a gaseous medium of solid particles, liquid particles or solid and liquid particles having
negligible fall-velocity/settling-velocity
group of two or more particles combined, joined or formed into a cluster by any means
fluid used to remove heat and reduce friction in a compressor
temperature at which water vapour begins to condense
organic compound consisting mainly of hydrogen and carbon
microbiological contaminants
viable colony-forming units, which can be of bacteria, fungi or yeasts
mixture of hydrocarbons composed of six or more carbon atoms (C6+)
small discrete mass of solid or liquid matter
particle size
length of the greatest distance between two external boundaries
pressure dewpoint
dewpoint of the air at the specified pressure
relative water vapour pressure
relative humidity
ratio of the partial pressure of water vapour to its saturation pressure at the same temperature
gas that is at a temperature below its critical temperature and that, therefore, can be liquefied by isothermal

4 Reference conditions
The reference conditions for gas volumes shall be as follows:
? air temperature 20 °C
? absolute air pressure 100 kPa = [1 bar ](a)
? relative water vapour pressure 0

5 Compressed air purity classes

5.1 General
The three major contaminants in compressed air are solid particles, water and oil; these are categorized by compressed air purity classes.
These compressed air purity classes group the concentrations of each of the above contaminants into ranges, each range being given its own purity class index. The range limits are aligned to those figures found in practice.
When required, all other contaminants should be stated directly by the specific concentrations allowed, or determined within the compressed air supply; see 6.4.

5.2 Particle classes
The particle purity classes are identified and defined in Table 1. Measurements shall be made in accordance with ISO 8573-4 and, when required, ISO 8573-8.
Where it is determined that there are particles with a size greater than 5 μm, then the classification of 1 to 5 cannot be applied.

5.3 Humidity and liquid water classes
The humidity and liquid water purity classes are identified and defined in Table 2. Measurements shall be made in accordance with ISO 8573-3 and, when required, ISO 8573-9.

5.4 Oil classes
The total oil purity classes are identified and defined in Table 3. Measurements for liquid oil and aerosols of oil shall be made in accordance with ISO 8573-2. It is considered that, for classes 3, 4 and X, the oil vapour
content is not expected to significantly affect the total concentration; therefore, the measurement of vapour is optional. Where it is deemed necessary to measure the oil vapour, then ISO 8573-5 shall be used.

5.5 Gaseous contaminants
No purity classes are identified for gaseous contaminants; the presentation of contaminant levels is given in 6.4. Values for gaseous contaminants shall be measured in accordance with ISO 8573-6.
5.6 Microbiological contaminants No purity classes are identified for microbiological contaminants; the presentation of contaminant levels is given in 6.4. Values for microbiological contaminants shall be measured in accordance with ISO 8573-7.


6 Designation

6.1 Designation principle
The designation principle of the purity class of compressed air at the specified measuring point shall include the following information in the order given and separated by a colon: ISO 8573-1:2010 [A:B:C]
A is the purity class for particles; see Table 1;
B is the purity class for humidity and liquid water; see Table 2;
C is the purity class for oil; see Table 3.
6.2 Unspecified designation
When a class for any particular contaminant A, B, or C is not specified, the designation shall be replaced by a hyphen. In the example given below, there is no humidity or liquid water classification. ISO 8573-1:2010 [A:–:C]
6.3 Class X designation
When the contamination level falls within class X, then the highest concentration of the contaminant shall be given in round brackets. In the example given below, the concentration of liquid water, Cw, is 15 g/m3.
ISO 8573-1:2010 [A:X(15):C]
6.4 Gaseous or microbiological contaminants designation (optional)
Gaseous and microbiological contaminants shall be identified as an additional item to the designation given in
6.1 as follows:
? ISO 8573-6 [contaminant & value & unit of measure];
? ISO 8573-6 [possible further contaminant & value & unit of measure];
? ISO 8573-7 [value cfu/m3].


EXAMPLE ISO 8573-1:2010 [A:B:C]
? [SO2 u 0,01 mg/kg];
? [CO2 u 1 mg/kg];
? [CO u 0,1 mg/kg];
? [5 (cfu)/m3] (where cfu designates colony-forming units).

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