The source of the solid grain in the air.

    There are two aspects of source of the solid particle in thecompressed air:
-  the ambient air
There are lots of suspended particulate matter in the air around us. Accordingto GB3095-1996 "ambient air quality standard", which regulates the average concentration of the suspended particulate matter in the air is less than 0.5mg/m3(standardstate). According to speaking in the industry, about 80% of the suspended particulatematter’s equivalent diameter is less than 2μm.In general, the air compressorinlet filter filter precision are also 2μm. Generally speaking, the filtration precision of the inlet air filter is also 2μm (2μm filtration precision isenough to protect the moving parts, and if the filtration precision is too high,it may lead to the pressure drop caused by negative pressure). so an estimated0.4 mg/m3 of suspended particulate matter goes into the compressed airsystem. 
- within the system
    On most occasions, solid particle caused by the inter compressed system isfatal. In China, most of the air compressor station use the common carbon steel pipe as compressed air transportation pipe.These pipes valves may produce:rust/rust mud, carbon deposition, welding slag, which are larger than the suspended particulate matter in the. In some occasions with higher requirements, such as medicine, electronic factory, the compressed air system ofair compressor station adopts the stainless steel or copper materials. at this kindof situation, the solid often comes from the atmosphere and air drying system(such as the dust of adsorbent dryer, etc.).