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Oil-Free Air Compressors

Kobelco KNW series oil-free air compressor

The challenge of keeping oil from getting into the product or process can made easier by oil free air compressors. Oil-free air compressors are used when there is a requirement for clean air. This is the case for manufacturers in the life sciences, food, and electronics industries as well as research labs and hospitals.

What it means to be “oil-free”

The story of “oil-free” can be complicated.  If by “oil-free” you mean; there is no oil in the compression chamber, that’s very easily done. If by “oil-free” you mean; the compressed air is about 400 times cleaner than normal atmospheric air, which meets ISO standards, that’s very easily done as well. That’s why it’s always important to know what you are really looking for when you discuss “oil-free.”

Misconceptions about oil-free air compressors

Now, about that “oil-free” compressor that has oil in it. The principle of an oil-free rotary screw compressor is similar to that of the lubricant-injected rotary screw compressor. The key difference is there is no oil being introduced into the compression chamber of an oil-free rotary screw compressor. Naturally, the bearings and gears that are not inside the compression chamber require lubrication. Lubrication may also be used for stator jacket cooling in air-cooled units. So, “oil-free” is limited to the compression chamber, which of course, is all that really matters.

Another common misconception is that oil-free designs save on filter and condensate costs. The reality is that with regard to solid particle content, an oil-cooled compressor with a refrigeration dryer and filter can achieve Class 1 ISO designation. On the other hand, a so-called oil-free compressor with a desiccant dryer only achieves a Class 3 designation. The lesson here is that each application needs to be understood carefully and the selection of equipment should be done carefully to build a system that meets the manufacturing requirements.

Kobelco KNW sereries oil-free air compressor
An oil-free compressor installation we completed for a customer in the bio-pharmaceutical industry.

Rotary screw oil-free air compressors

A two-stage rotary screw compressor provides completely oil-free air because there is no oil in the compression chambers. Kobelco KNW Series oil-free air compressors employ a patented asymmetric super rotor design that provides the lowest power consumption per cubic foot of compress air. They also meet the NFPA99 requirements for use as a medical air compressor. A touchscreen display and the low sound level are ideal for applications where ambient noise poses operational difficulties. The 2-stage design of Kobelco’s oil-free compressors operating at pressures of 40–150 PSIG and capacities from 170–2400 SCFM are ideal for pharmaceutical, food processing, and semiconductor applications. The design delivers energy and cost savings through high efficiency rotors and anti-friction bearings for long life and smooth operation. Incorporating an air pressure operated thrust balance piston on each stage reduces axial thrust. This arrangement minimizes thrust loading thus increasing bearing life.