Air Compressors > Oil-Free

Challenge: How to keep oil from your compressed air system from getting into your product, your process and your hair; by not having any oil in the compression chamber to begin with or by cleaning it to meet the ISO standards for industries such as medical, food and semiconductor.

Myth: The belief that oil-free compressors save on filter and condensate treatment costs.

Learn from us: 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. But, it’s always important to know what you are really looking for when you discuss “oil-free.”

Believe it or not, there are highly effective compressed air system designs that operate efficiently without any lubricant in a rotary screw compressor. A centrifugal compressor also operates without a lubricant. And even reciprocating compressors can be oil-free. That’s a good thing, because for some industries and processes, it’s vital not to have oil to contend with. The principle of an oil-free rotary screw compressor is similar to that of the lubricant-injected rotary screw compressor but, without any oil being introduced into the compression chamber.

Dry-Type v. Water-Injected
There are two types of oil-free systems. The first is dry-type. In the dry-type compressor, the intermeshing rotors are not allowed to touch and their relative positions are maintained by means of lubricated timing gears external to the compression chamber. Since there is no injected fluid to remove the heat of compression, most designs use two stages of compression with an intercooler between the stages and an aftercooler after the second stage.

In the water-injected type compressor, similar timing gear construction is used, but water is injected into the compression chamber to act as a seal in internal clearances and to remove the heat of compression. The injected water, together with condensed moisture from the atmosphere, is removed from the discharged compressed air by a conventional moisture separation device.

Now, about that “oil-free” compressor that has oil in it. 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.

Also, about that “myth” that oil-free designs save on filter and condensate costs. The reality is that with regard to solid particle content, while an oil-cooled compressor with a refrigeration dryer and filter can achieve Class 1 ISO designation, a so-called oil-free compressor with a desiccant dryer only achieves a Class 3 designation. The lesson 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.

Hope Air Systems responds: Hope Air Systems distributes a wide range of “oil-free” air compressors. These include centrifugal, rotary, and specialty piston reciprocating compressors, such as those used in dentists offices. Major brands of oil-free systems include Kaeser, Kobelco, FS-Elliott and others. From PET bottle blowing systems requiring 400 HP or more down to small systems for a dental office, there is an appropriate system available.

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Oil-free Rotary Screw
The Kobelco KNW Series of oil-free rotary screw compressors are available in two-stage, air or water-cooled designs with horsepower ranging from 40HP to 500HP. The Kobelco systems are noted for long operating life, minimum maintenance and low operating costs. These systems are designed and built in the United States and are delivered ready for start-up.

The two-stage rotary screw compressor provides completely oil-free air because no oil is allowed in the compression chambers. Kobelco employs a patented asymmetric super rotor design that provides the lowest power consumption per cubic foot of compress air.

Oil-free Piston Reciprocating
The Kaeser line of oil-less reciprocating air compressors are suited for dental offices and other applications requiring oil-free air. These systems provide high quality, reliable air, which contributes to overall product quality and prevents premature wear on costly air-powered instruments.

Clean, dry air is provided through the built-in air inlet filters and air aftercoolers which are standard on all Kaeser KT and Duplex models. Dryers are available to remove moisture, preventing oxidation and corrosion. Plus, these oil-less units can be configured with external clean air treatment for larger installations.

Oil-free Centrifugal
FS-Elliott produces a line of oil-free engineered air centrifugal compressors suited for food and beverage processing, automotive manufacturing, pharmaceutical, electronic, mining and many other critical fields requiring oil-free air. With only the gear and rotors as moving parts, there are no lubricated parts in the air passage – so you can count on getting oil-free engineered air.

Centrifugal compressors are popular because they operate reliably for long periods of time with minimal maintenance. Among the features of a centrifugal design are, inherently low vibration, no direct wearing of parts, optimum clearances between rotating and stationary parts, no oscillating load and an integrated engineering package design.

Hope Air Systems has extensive experience with all types of air compressor systems. Let us help you decide which type of system is best for your applications and rest assured that we can help you select the equipment that’s right for you.

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