There are 2 different types of pumps for air compressors – oil-less pumps and oil-injected pumps. However, there are very low oil models and ‘really’ no oil models.
In general, the traditional oil-injected compressors are fine for most jobs, and tend to be lower maintenance. They tend to last longer in use, and are not as loud as the oil-less pumps. The problem is that a measurable amount of oil mist does make its way into the compressed air output.
The choice really boils down to whether what you’re doing with the air can withstand a tiny amount of oil or not.
What are the different air purity classes?
Not all oil-free air compressor pumps are created equal. There are some applications where the oil contamination imparted by traditional oil-injected pumps would be unacceptable, but the highest oil-free standards aren’t necessary. There are other applications – like formulating pharmaceuticals or manufacturing semiconductors – where as close to zero oil as possible is required.
Technically Oil-Free Air (ISO Class 1)
This was once the highest classification for oil-free air compressor output, but things have changed. These days, class 1 is really the minimum level one would consider for oil-sensitive applications.
On a technical level, ISO class 1 air compressor output can contain no more than 0.01 mg of oil per cubic metre of air, at a pressure of 1 bar and a temperature of 20OC. As of the 2010 update to the regs, this measure includes all forms of oil contamination: vapour, aerosol and liquid droplets.
Many ‘Technically Oil Free’ air compressors are oil injected units with filtering put in place to catch the majority of their slight oil contamination before it leaves the machine. Others are oil-less units which do not meet the very high standards explained below.
Oil-Free Air (ISO Class 0)
Class zero ‘truly oil free air’ was added to the books when the demand for more purity and the technical capacity to deliver it resulted in better grade ‘oil-less’ air compressors hitting the market.
The standards for a Class 0 air compressor are absolute – 100% oil free air output. This is needed for the most oil-sensitive applications. However, as noted above these units are more expensive, tend to demand more maintenance and can offer a shorter working life – so don’t choose an ISO Class 0 air compressor unless you really need it!
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