Types of compressors: oil-free and oil lubricated air compressors

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Types of compressors: oil-free and oil lubricated air compressors

In our previous article we explained the difference between piston compressors and rotary screw compressors. However, there is also an important difference between oil-free and oil lubricated compressors. We’ll discuss both in this article.

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Specific types of compressors

In the case of piston compressors as well as rotary screw compressors, there is a choice between the oil-lubricated and oil-free kind. Both types have their own specific advantages and disadvantages. First, let’s see why both compressors need lubrication in the first place.

Piston compressor vs. rotary screw compressor

Type of compressor: oil-lubricated or oil-free air compressor

A piston compressor - obviously - uses a piston to compress air and deliver it at high pressure. Essentially it works according to the same mechanism as a combustion engine. A central shaft drives the pistons. When the piston is drawn backwards, gas enters the compressor through a valve. The gas is then injected into the cylinders of the pistons and the movement of the pistons compresses the air. In piston compressors, some sort of lubrication is needed to ensure smooth operation and prevent overheating.

A rotary screw compressor, on the other hand, uses rotors to compress air. Male and female rotors turn in opposite directions, thus trapping the air between them. There is no valve system. Overheating is not an issue here, but the fact remains that rotary screw compressors can deliver a continuous airflow: they need lubrication to keep going at full throttle, 24/7.

What about the types of lubrication?

Oil-lubricated air compressors: pros and cons

In oil-lubricated air compressors, oil is used to keep everything running smoothly and prevent overheating. This, however, has a few disadvantages

  • The compressed air has traces of oil. This might be an issue in certain applications. However, an additional filter can be installed to ensure that all traces of contaminating oil are removed;
  • Oil-lubricated (piston) compressors are heavy and less easy to move around;
  • Oil-lubricated air compressors are often quite bulky and take up a lot of space.

air compressor

Because of these reasons, oil-lubricated air compressors are often used in industrial settings.They also offer a few advantages

  • Little maintenance is needed and solving technical problems is often quite simple;
  • Oil-lubricated air compressors have a long lifespan;
  • Because of the thorough lubrication, they produce little noise or heat;
  • They can be used in more extreme situations and for heavy-duty work.

Oil-free air compressors

Oil-free air compressors use other means of lubrication, for instance pre-lubricated cylinders and an intercooler. An oil-free air compressor does technically contain oil, but that won’t come into contact with the compressor. The oil-free air compressor has a few disadvantages

  • Oil-free air compressors generate more noise and heat than oil-lubricated compressors;
  • They have more maintenance requirements;
  • They have a shorter lifespan;
  • They are not quite suited for heavy-duty use.

air compressor

Oil-free air compressors are especially suitable in non-industrial settings like dentistry or smaller workshops where contamination is an issue. They are also particularly useful for home or DIY-applications. The advantages of an oil-free compressor: 

  • They are smaller and easier to move around;
  • They deliver clean air without traces of oil;
  • No manual lubrication is required;
  • They cost less than oil-lubricated compressors.

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Read more about air compressors in related articles

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