In recent weeks we have looked at some specific applications for which oil-free air compressors may be preferable – for example, dental air compressors that must produce very clean and dry output for use inside patients’ mouths.

But how exactly do oilless air compressors work, and why don’t they simply seize up as an engine’s moving parts would without oil?

For most applications, lubricated air compressors are perfectly acceptable – the oil reduces friction between moving parts, and this can improve efficiency, reduce maintenance demands, and may have safety implications in explosive environments where friction could raise heat levels by an unacceptable extent.

However, lubricated air compressors inevitably introduce a certain degree of oil contamination into the air they output, including microscopic aerosol oil droplets, clouds of oil vapour or mist, and even liquid oil that may form on the inner walls of the compressor output pipe and gradually creep to the nozzle.

Oil-free air compressors eliminate these problems in the simplest way possible – by not using oil. In this sense, it is an elegant solution to any concerns about oil contamination in a compressed air supply.

But that still doesn’t explain how oilless air compressors work.

This too is very simple, however: rather than using oil to lubricate the system and reduce the friction that arises from contact between moving parts, an oil-free air compressor is manufactured to much finer tolerances.

Air compressor parts such as the rotors typically do not touch at all in oilless air compressors, instead passing very very close to one another without making contact.

The result is no major loss of efficiency, but a system with no oil contamination in its output, and no friction arising from direct contact to increase the internal temperature or cause damage to the rotor surfaces.

Finally, remember oil is not the only way to reduce friction on a surface; oil-free air compressor parts may be Teflon-coated where appropriate, and this provides a further way to reduce any friction forces that might be exerted upon them.