Oil-free compressors are used to produce a range of sensitive products, from semiconductors to medication to paper. Even trace amounts of oil in these applications can damage products and potentially people. There is a lot of terminology used in the market that is not always straightforward, and this holds true when discussing oil-free compressors.
Terms like oil-free, oil-less, Class 0 and “technically oil-free” are frequently used to imply that a compressor meets certain standards. But even though these terms sound similar they have key differences that — if not taken under consideration — can lead to unintended consequences.
First, let’s take a moment to break down some of the above vocabulary. Oil-free and oil-less are both used to describe compressors that do not use any lubrication in the compression chamber. While the first two terms describe a type of compressor, Class 0 and “technically oil-free” express how clean the air is after compression. Though they are close in meaning, there are a few important differences between the two.
Class 0 and technically oil-free air
Class 0 and “technically oil-free” compressed air are different. Class 0 oil free compressors can guarantee 100 percent oil-free air. While they may have a higher initial price point, these compressors are much safer for sensitive applications. On the other hand, “technically oil-free” compressors have a high chance for contamination, because they are actually lubricated compressors that include oil-removing filters. Unlike their Class 0, oil-free counterparts, “technically oil-free” air compressors are ranked as Class 1.
ISO Class 0 and ISO Class 1
The International Organization for Standardization (ISO) sets forth worldwide standards for proprietary, industrial and commercial purposes. Compressed air has its own set of ISO standards. Depending on air ultimate air purity (determined by number of particles per cubic meter as a function of particle size), compressors can be ranked from ISO Class 0-5.
The original version of ISO compressed air purity standards (1991) was ‘made by and made for’ the filter manufacturers. The standard defined five classes of oil concentration, the best of which was Class 1. Class 1 specifies an oil concentration of ? 0.01 mg/m3 at 1 bar(a) 14.5psia and 20oC (68F), and conformance to these criteria is sometimes called “a technically oil-free solution.”
However, these standards were edited in 2001 and were further updated in 2010. The current standard sets limits on total oil content (aerosol, liquid and vapor), and a specific standard was introduced on measurement of oil vapor. A new class (Class 0) was added to cover more stringent quality requirements.
ISO Class 0 is the cleanest choice
There are myths floating around the industry that lubricated compressors and filters are “technically oil free” and that air quality from oil-injected compressors with filters is often better than from oil-free compressors. These ideas are simply untrue, and purchasing an oil-free compressor based on incorrect information can cause inadvertent damage to sensitive applications and products.
When selecting an oil-free compressor, make sure you’re choosing a Class 0 oil-free compressor and not a “technically oil-free” option. With Class 0, you can be sure that absolutely no contamination will reach your end-use.