... the „most controversial standard“ of compressed air treatment technology
The subject of the ISO 12500 series are test methods for water separators and compressed air filters at laboratory and defined operating conditions (test conditions). The target is to generate standardized and thus comparable product performance figures, allowing the comparison of products in regards to their performance or economic efficiency.
Filters for compressed air— Test methods—Part 1: Oil aerosols
First edition (2007)
ISO 12500-1 specifies test and inlet (challenge) conditions for compressed air filters for liquid oil separation. ISO 12500-1 determines the residual (liquid) oil content and the according differential pressure of a compressed air filter at the standardized test and inlet conditions:
- nominal volume flow at 7 bar and 20°C
- inlet challenge concentration of 10 mg/m³ or 40 mg/m³ of oil aerosols
- of viscosity grade 46 and
- with an average (normal mean) particle size of 0,15 µm to 0,4 µm (by number)
- determination of the residual (liquid) oil content at the outlet of the compressed air filter according to ISO 8573-2
- three examples of each filter shall be tested while repeating each test three times (total of 9 tests per size and filtration grade)
An inlet challenge concentration of 10 mg/m³ as well as the requested particle size distribution is not really representative for modern compressed air systems.
For liquid separation in compressed air filters many interlinked physical processes are involved, resulting in a multi-dimensional array of working conditions while ISO 12500-1 just supplies a result for one working point in this multi-dimensional array. A “good” filter when tested according to ISO 12500-1 thus may deliver a “bad” performance in a deviant real life operation and vice versa. The result of ISO 12500-1 thus may be misleading and may conclude to a wrong assignment of products in regards of “good” or “bad”.
A compressed air filter series offering 12 filter sizes and 3 filtration grades would require the test of 108 filter elements or 324 total tests. Even a 24h continuous testing would last at least 6 months.
Filters for compressed air— Test methods—Part 2: Oil vapours
First edition (2007)
ISO 12500-2 specifies test and inlet (challenge) conditions for compressed air filters for oil vapor adsorption. ISO 12500-2 determines the breakthrough time of a compressed air filter at the standardized test and inlet conditions:
- nominal volume flow at 7 bar and 20°C
- inlet challenge concentration of 1000 mg/kg n-hexane
- determination of the n-hexane content at the outlet of the compressed air filter according to ISO 8573-6 ; time until an n-hexane concentration of 1 mg/kg is measured at the outlet of the compressed air filter (“breakthrough”)
- three examples of each filter shall be tested
The defined inlet challenge concentration is not suitable for compressed air filter and results in breakthrough times of a few seconds only. Alternatively, sometimes an inlet challenge concentration of 100 mg/kg and a breakthrough limit of 80 mg/kg is applied.
ISO 12500-2 doesn’t consider the equilibrium (adsorption isotherm) of activated carbon and thus the changing adsorption behavior of activated carbon at different load conditions.
At the same time the defined inlet challenge concentration is 10,000-times higher than the typical challenge concentration in a real life compressed air system. A “good” filter when tested according to ISO 12500-2 thus may deliver a “bad” performance in a deviant real life operation and vice versa. The result of ISO 12500-2 thus may be misleading and may conclude to a wrong assignment of products in regards of “good” or “bad”.
Filters for compressed air— Test methods—Part 3: Particulates
First edition (2009)
ISO 12500-3 specifies test and inlet (challenge) conditions for compressed air filters for particle separation. ISO 12500-3 determines the (fractional) efficiency and the according differential pressure of a compressed air filter at the standardized test and inlet conditions:
- nominal volume flow at 7 bar and 20°C, alternatively at atmospheric conditions
- inlet challenge agent
- fine: NaCl (solid) or DEHS (liquid) particles according to EN 1822-1, EN 1822-2
- coarse: test dust according to ISO 12103-1, A4
- determination of the efficiency
- fine: particle counter according to EN 1822-2 and EN 1822-5
- coarse: suitable particle counter or microscopic analysis
- three examples of each filter shall be tested
ISO 12500-3 allows to determine the efficiency of a compressed air filter either at pressure or at atmospheric conditions while efficiency depends on the working pressure. Thus for comparison it is important to pay attention if the test was carried out at 7 bar or 0 bar working pressure, respectively.
Filters for compressed air— Test methods—Part 4: Water
First edition (2009)
ISO 12500-4 specifies test and inlet (challenge) conditions for compressed air water separators. ISO 12500-4 determines the (total) efficiency and the according differential pressure of a compressed air water separators at the standardized test and inlet conditions:
- 25%, 50%, 75%, 100% and 125% of nominal volume flow at 7 bar and 20°C, alternatively at a higher working pressure
- inlet challenge of 2 ml/min of water per l/s of nominal volume
- determination of the residual water at the outlet of the water separator according to ISO 8573-9
- test time of at least 10 minutes
- test for each flow condition, repeating each test three times (total of 15 tests)
The inlet challenge of water is only defined by its total quantity, but not how the water is introduced to the compressed air. Thus, water is typically challenged as wall flow. Accordingly, ISO 12500-4 doesn’t supply a result for droplet or aerosol separation of the compressed air water separator.
All tests are performed at one specific working point of the compressed air filter and thus are not representative for the performance of the filter at real life working conditions deviating from the defined test conditions. Thus typically there is no relation between an ISO 12500 test result and the compressed air purity achieved by the filter in a real life compressed air system.
Most ISO 12500 standards refer to test methods of the ISO 8573 series.
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- The defined test methods of ISO 12500 are more a kind of „worst case scenarios” for compressed air filters and thus offer only a low benefit for real life applications
- Accordingly, the determined results are poorly applicable up to misleading (without specific knowledge may lead to a wrong assignment of products)
- Furthermore, ISO 12500 demands many extensive and several times repeated tests, resulting in enormous test efforts
- Consequently, the ISO 12500 series in its actual edition suffers from a poor acceptance
- Primarily ISO 12500-1 and ISO 12500-2, but also ISO 12500-3 and ISO 12500-4 require an extensive revision
Standards are protected by copyright .
Thus they are distributed exclusively, e.g. in Germany by Beuth-Verlag ( www.beuth.de ).