5 common myths about oil free compressors

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Specifying the right compressor or identifying a suitable replacement can become a daunting job.

Before even considering different types of compressor, you’re often faced with the question, ‘does it need to be oil free?’

A recent report shows the oil-free segment now holds the largest share of the compressed air market. And it will grow at a faster rate than its lubricated counterpart. These trends are driven by the fact that some compressed air users believe that oil-free options offer improved air quality, as well as reduced costs for purification equipment and maintenance.

There are pros and cons for both oil lubricated and oil free compressors, misconceptions about oil free have spread far and wide. So, we’re going to tackle some popular myths about oil free air compressors – and oil free compressed air in general!

Myth 1: Oil free compressors provide contaminant free air

False! While oil free compressors reduce the amount of oil that needs to be removed from compressed air, there are many contaminants found in atmospheric air and throughout the entire system.

Generally, there are 10 contaminants found in a typical compressed air system:

  • Water vapor
  • Oil vapor (from atmosphere)
  • Oil vapor (from lubricated compressor)
  • Atmospheric dirt
  • Microorganisms
  • Oil aerosols
  • Condensed liquid water
  • Water aerosols
  • Rust
  • Pipescale

The use of an oil-free compressor alone will only remove one contaminant. Yet, oil vapour can still enter the system if its present in the atmospheric air such as from vehicle exhausts and industrial processes. This is something you can’t control.

So, oil free compressors don’t guarantee contaminant free air. Regardless of the type of compressor you select, further filtration and purification is required.

Myth 2: The air compressor is solely responsible for contamination in the compressed air system

False! Contamination in a compressed air system comes from four different sources:

  • Atmospheric air
  • Air compressor
  • Compressed air receiver
  • Compressed air distribution pipework

So, if the air drawn into the compressor is already contaminated by oil vapour in the ambient air, the oil free compressor will be unable to remove it.

This counter argues the common practice of removing downstream filtration when using an oil-free compressor. Installing filters is essential for removing existing contaminants and reaching the purification required for the application.

Myth 3: Oil free compressors do not use oil

False! The biggest myth is that oil free compressors do not use oil. Oil free compressors do not use oil in the compression chamber, so oil doesn’t contact the air being compressed. But oil can still be used to cool the compressor and lubricate the moving parts. Have no fear, sealing systems are used within the compressor to block any oil from entering the compressed air system.

Myth 4: Oil free compressors are more expensive

Up for debate! So, oil free compressors do have a higher initial capital cost than oil lubricated alternatives, by up to 40-50%.

Now let's consider the lifetime cost. For sensitive applications that need oil free standards of compressed air, the lifetime cost could be less than ‘technically oil free’ alternatives. The risk of contamination from ‘technically oil free’ options is always there. Can you risk failure if it results in downtime, loss of production and damage to product? What would be the cost of this?

Myth 5: Oil free compressors provide compressor air to Class 0

Up for debate! ISO8573-1 is the International Standard for Compressed Air Purity. This provides differing classifications for air quality. Class 0 is the strictest of the classifications. Many compressor manufacturers claim oil-free compressors are compliant with Class 0.

Class 0 does not mean zero contamination. Testing a compressor in sterile conditions, the contamination detected at the outlet would be minimal. Now take the same compressor and install in an industrial environment. The level of contamination will be dependent upon what is drawn into the compressor intake, making the Class 0 claim invalid.

And what about the journey throughout the system? Just because Class 0 was achieved at the outlet of a compressor, doesn't guarantee that the air will still be Class 0 at the point of use. Don't forget contamination already in the air receiver and distribution piping will contaminate the compressed air.

It is wrongly assumed that Class 0 refers only to oil, whereas ISO8573-1 has classifications for Particulate, Water & Oil. When claiming Class 0, specifications should state which contaminant the Class 0 refers to.

After reviewing the myths and giving some insight into them, it’s clear that oil free compressors and air quality should be considered simultaneously and, on a case-by-case basis. Some useful questions to ask are:

  • What quality of air do I need to achieve?
  • Where is my compressor located/going to be located? How will the atmospheric air affect it?
  • What impact would oil contamination have on my application?
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