The source of the oil in the compressed air.

     We know that there are three kinds of pollutants in the compressedair, that is, water, oil and dust.The source of the three pollutants are different:
- water, is one of nature inherent in the air; 
- oil: mostly comes from air compressor (in serious air pollution areas, therealso contain oil pollutant). 
- solid particles: some from the air, some from inside the compressed airsystem. 
     Compressed air drying equipment (suchas refrigerated compressed air dryer, adsorption dryer, etc.) can remove the moisture in the air, and the oil and solid particles can be removed by the compressed air filters. 
     The oil in the compressed air is inweak acid. so it not only can't play a role in lubrication for gas equipment, butto cause corrosion. It can cause gas equipment failure in a certain period oftime. 
     In some strict places, such as apneumatic control system, a drop of oil may change the spiracular, which makes the normal automatic production line to paralysis.Sometimes, the oil will alsomakes the sealing ring of pneumatic expand, causing delayed operation, it mayeven blocks.In the process completed by air, such as blowing shaped parts, oil pollution will cause the appearance defects or appearance pollution.
    Compressed air is produced by a compressor. most of the air compressor uses lube oil for lubrication and cooling its moving parts (such asscrew, piston, etc.). The lube oil directly contacts with the high temperature airin the compressed dryer.


    Oil exists in the compressed air in the conditon of  "oil drop", "oil mist(aerosol)" and "oil vapor".
    For example, the working process of the helical-lobe compressor. 
   Air is sucked into air compressor. First, it goes through the suction filter,then goes into the compression chamber to be compressed, and then goes into theoil and gas separator if reach the certain compressure(Now the temperature ofthe compressed air is about 100 ℃). The lubricating oil in the compressed air is recycled. Thecompressed air being seperated goes into the post-cooler to be wind cooled to40 ℃, and the condensation water drains through the automatic drainer. 
    While the air is compressed, the lubricating oil is sprayed into the compression chamberto lubricate and cool the screw. The lubricating oil goes into the oil and gas separator with compressed air. The lubricant separated goes into the oil cooler.Afte being cooled, it is pumped into the compression chamber again for recycling.
Although all the oil air compressorhave has oil and gas separator, thecompressed air temprerature in the "oil and gas separator" is higher,which means the oil vapor partial pressure is high. But the oil vapor cannot be separated in the "oil and gas separator". The compressed air being cooled by the post-cooler, the partial pressure of the oil vapor in the compressor is reduced. Some part of the oil vapor condensates into oil mist. Therefore,there should be oil in the compressed air which is drained through helical-lobe compressor. We can prove it according to the situation that theair compressor should be added lubricating oil in a certain period of time.
The oil dust in compressed air is not high, so generally we use mg/m3 torepresent (that is, the amount of oil in a cubic meter of compressed air), and wealso use PPMW (weight ratio) and PPMV (volume ratio). 
   Besides the oil in the compressed air from the air pressure, there is samll amount from the surrounding air. Due to the air pollution, there is about 0.05PPM to 0.25 PPM of oil in the air. Strictly speaking, there is oil in the compressed air which is drained by oilless air compressed.