Oil-free screw compressors

Oil-free screw compressors, also known as drying compressors, are essential for some productions where there must be no risk of contamination.

Estimated Reading Time: 2 minutes

April 24, 2023

Oil-free screw compressors stop oil contamination

What happens when you lubricate an air compressor with oil? You keep your air compressor running smoothly. But you also mix oil into your compressed air. There are various techniques that remove the majority of this oil, but in the end, there are still trace amounts of oil present.

Is this a problem? Not for most industries. But various sectors simply cannot have any oil contamination in their compressed air. The electronics, medical and food and drink industries are the best examples; you probably prefer food that doesn’t taste like engine oil.

And that is why oil-free air compressors are the heroes in this blog post. They make sure there is zero risk of contamination.

How do oil-free compressors work?

One of the reasons we use oil in air compressors is its lubricating effect. We don’t want metal scraping against metal, and with a bit of oil, we help to stop this. But when oil is outlawed, like in the medical, food and drink industries, you’ll basically want an oil-free compressor.

An oil-free reciprocating compressor has permanently lubricated bearings. The pistons use grease-free rings that are usually made from carbon fibre or coated in Teflon. The bearings and piston rings need to be replaced more frequently than with an oil-injected compressor. But this is a relatively small price to pay for food that doesn’t taste of engine oil.

An oil-free screw compressor—also known as a dry screw compressor—takes a different approach. In this case, the need for lubrication is avoided with the use of timing-synchronising gears for the screws. They minimise the contact the screws have with each other, and as such, avoid the need for lubricating oils. 

How do oil-free compressors stay cool?

ALUP OF oil free compressor

ALUP's OF Oil-Free Compressor

Oil-free air compressors do not cool their compression chambers. At an operating pressure of about 300 kPa, the temperatures rise to about 200°C. All good… Except that most industrial processes work with air pressures of about 700 kPa. Raise the pressure this high in a single step and temperature will become an issue.

The solution? Raise the pressure in multiple steps. As such, most oil-free compressors compress air in multiple stages, allowing the compressed air to cool between these stages. 

What happens when you cool air?

When it’s heated, air holds more moisture. As it cools, this moisture collects to form condensation, or if you prefer, water. Needless to say, you have to remove this. And this is where we look at air dryers. While they dry air, they often cool it at the same time. 

There are three main types of dryers that do this:

• Refrigerated dryers

• Membrane dryers

• Desiccant dryers

Want to know more about air dryers? Or do you have questions? We discuss them in more detail here

Would you like to know more about oil-free compressors? Are you wondering whether you need to go oil-free? Get in touch with us at ALUP. We look forward to helping you out.

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