When using an oil lubricated compressor without filtration, oil enters the connected compressed air network with an assumed concentration of c = 10mg/m3. With an efficient depth filter, however, a residual oil concentration of 0.01mg/m3 is achieved, other conditions being equal. Until recently, there were no standards covering the measurement of residual oil in compressed air. However, recent acceptance of ISO 8573.2 now gives the user a means of determining oil aerosol content. Requirements regarding oil content in compressed air are indicated in ISO 8573.1 : 2001 (E)
Table 4.8.1.1| Class | Oil/Content mg/m3 |
|---|
| 1 | 0.01 |
| 2 | 0.1 |
| 3 | 1 |
| 4 | 5 |
| 5 | - |
| 6 | - |
Technical oil free compressed air is defined by the values of a residual oil content < 0.01 mg/m3The m3 datum here refers to atmospheric air at a pressure of 1013 mbar and a temperature of 20°C. On closer examination, even the use of oil free (non lubricated) compressors cannot guarantee absolute freedom from oil in the compressed air, for the compressor draws in ambient air of varying quality and concentrates hydrocarbon and other airborne impurities.
