The Part 2 test measures aerosols and liquids. Testing can be done through partial flow (B2) or full flow (B1) methods (see below). The Part 5 test measures vapors only. Both parts are necessary to obtain ISO 8573 CLASS 0 certification. This means that all three sources of oil contamination – aerosol, vapor and liquid – have to be measured.
Both methods are acceptable for aerosol and liquid measurement according to ISO 8573-1 Part 2 The B2 method targets only the center of the air flow. Oil aerosols are registered but oil that sticks to the pipe wall (wall flow) is not detected. Most air compressor manufacturers still prefer this less stringent method. The B1 method examines the entire air flow to measure both aerosols and wall flow. This comprehensive test method was used on the Atlas Copco range of oil-free air compressors. Even so, no traces of oil were found in the output air stream.
This solution is often referred to as “technically oil-free air”. However, even under optimum conditions and with several stages of oil removal, the air quality with regard to oil is suspect. To achieve even barely acceptable air quality with oil-injected compressors, it is necessary to have air cooling devices and several stages of oil removal with multiple components. A failure of any of these components or inadequate maintenance can result in oil contamination of a process. With oil-injected compressors there will always be a risk of contamination and the possibility of severe consequences for the business.
One aspect influencing the efficiency and purity of air systems is temperature. When using oil-injected compressors with oil removal filters, oil carryover through filter media increases exponentially according to the temperature at the filtration interface. If the ambient temperature in the compressor room increases to 30°C, the compressor outlet temperature could be 40°C with the oil carryover 20 times the specified value. Such temperatures are not unusual even in colder countries, where the compressor room temperature is substantially higher than that outside. Temperatures also cause an increase in the vapor content of the air, some of which can carry through to the end product. Moreover, high temperatures shorten the lifetime of activated carbon filters. An increase in temperature from 20°C to 40°C can cut filter lifetime by up to 90%. Even worse, the activated carbon filter does not warn the user when it is saturated. It will simply allow oil to pass on to processes. For Atlas Copco’s oil-free compressors, air quality is independent of temperature.
Ambient air has very small traces of oil coming from vehicles and industrial sources. However, in contaminated areas, oil content does not normally exceed 0.003 mg/m3. This is borne out by tests conducted by the TÜV near a factory with heavy machining activity (including turning, milling, grinding and drilling). Heavy vehicular traffic and a garbage incinerator were in the vicinity. Aspirated by an oil-free compressor, this extremely low level of atmospheric oil is almost completely washed away by the condensate in the intercooler and aftercooler, resulting in pure oil-free air for your process.