Oil-free and Class 0 air poorly understood, says Mattei 07 June 2013

Plant managers are including using the terms 'oil-free' and 'Class 0' on tender documents for air compressers, but Mattei says it is concerned that some do not have a clear understanding about what they mean.

Andy Jones, general manager of the rotary vane compressor manufacturer, explains that ISO8573-1:2010 is the international standard for specifying compressed air quality, detailing contaminants quantities – with solid particulates, water and oil having their own classes.

"The Class 1 standard for oil, which states that in each cubic metre of compressed air there should be no more than 0.01mg of oil, is suitable for critical applications, such as breathing, medical and food," states Jones.

"However, there is also a more stringent Class 0... Despite its name, class 0 does not equal zero contamination... When used in isolation the term Class 0 is meaningless. Meanwhile, the phrase 'oil-free' relates to a type of compressor, rather than a specific class of air."

Historically, only very sensitive environments – such as pharmaceutical, and food and drink manufacturing – have required compressed air with a high standard of purity, he says.

But with the shift towards compressed air users requesting 'oil-free' and 'Class 0' air for more standard applications in recent years, Jones says it's time to flag up the issues arising.

"It's vital for specifiers to consider whether Class 1 or Class 0 air is truly required – and whether it is needed for the entire system or just part of it," warns Jones.

"Because the more stringent the purity, the more costly it is to achieve it, especially if the oil-free compressor route is taken," he explains.

"Oil-free compressors are more expensive than oil-lubricated equivalents, in terms of the capital outlay and maintenance, as well as the amount of energy they use. In fact we'd suggest oil-lubricated compressors are 10—15% more energy efficient than oil-free machines," he continues.

And as typically some 75% of the cost of an air compressor over a five-year period comes down to its electrical consumption, choosing an oil-lubricated compressor can offer significant savings in energy costs.

"Also, since oil-free compressors don't use any lubricating oil in the compression chamber, many end users assume they will provide oil-free, Class 0 air. However, this is not the case," states Jones.

"For an oil-free compressor to ensure Class 1 or Class 0 purity, downstream filtration will nonetheless still be required – because outside of laboratory conditions the air being drawn into a compressor can never be entirely clean and free of hydrocarbons or other contaminants."

Jones insists that users need to understand that, providing there is an adequate level of filtration, an oil-lubricated compressor can deliver high standards of air purity.

"Modern oil removing devices can reach exceptional levels of performance... In fact, they are capable of making compressed air 400 times cleaner than the air we breathe," he states.

There can be legitimate reasons for end users requesting Class 1 and Class 0 air. However, before investing in costly equipment, Mattei is urging plant and factory managers to thoroughly assess why such high standards of purity are needed, and whether they are required for the whole plant or just isolated areas," says Jones.

It is also worth investigating whether it would more appropriate, cost-effective and efficient to achieve Class 1 or Class 0 with an oil-lubricated compressor and filtration, rather than with an oil-free compressor – which will still require filtration.

Brian Tinham

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Mattei Compressors Ltd

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