Screw Compressor element oil-free type

Easy to understand info on Rotary Screw Air Compressors

A reliable Compressed Air Source for your factory!

On this page I will tell you about the pros and cons of the rotary screw compressor, what to look for when buying one and common breakdowns that might occur during operation. The rotary screw compressor uses two rotors (helical screws) to compress the air. There’s a ‘female’ rotor and a ‘male’ rotor. The rotors are of different shape, but fit each other exactly.

When the rotors start turning, air will get sucked in on one side and gets ‘trapped’ between the rotors. Since the rotors are continuously turning, the air gets pushed to the other end of the rotors (the ‘pressure side’) and new fresh air gets sucked in. Because this is a continuous process, this kind of compressor doesn’t make a lot of noise; it runs quiet and smoothly.

Here you will find more information about screw compressor elements.

Compared to piston-type reciprocating compressors, the screw compressor is much more expensive. But it will run 24/7 and 365 days a year without any problems. The capacity (liters of air per second) of screw compressors are generally much bigger compared to piston-type compressors.

When you require a lot of air in your workshop or factory, this type of compressor is usually the best choice!

Oil-free or Lubricated

The rotary screw compressor is available in an oil-injected and oil-free versions. The basic principle is the same (the rotors ‘push’ the air to one side), but they are quite different machine.

The big difference is the design of the compressor elements, the part where the actual compression takes place. The oil-injected version needs oil to operate properly; the oil-free version doesn’t need oil.

Because of this, the rotors used in oil-free screw compressors are of superior quality with very little space in between them. They do not touch each other though; otherwise they would wear-down too quickly. For this reason, they are a lot more expensive. Oil-injected models are by far the most common of screw-type compressors.

Oil-free models are used for specific special applications. I’ve mostly seen them on big factories like oil/gas or chemical refineries, big food factories or other places where the compressed air must be 100% oil-free (otherwise it could contaminate the food, product or chemical process).

Oil-injected Rotary Screw Compressors

How do they work? As its name implies: there’s oil injected in the compressor element (where the actual compression takes place), during the compression of the air. This oil is later removed by the oil separator, so we end up with clean compressed air.

Of course there’s a lot more to it, learn how an oil-injected rotary screw compressor works.

Although 99,9% of the oil stays inside the compressor, there is always a little oil that passes through the separator and leaves the compressor with the compressed air. This is called “oil carryover”.

Oil-injected screw compressors therefore don’t produce oil-free air and they can’t be used in places where oil-free air is needed. But for most factories, workshops and machinery, the small oil-carryover of the compressor is not a problem. In fact, it helps to prevent again rust (inside the compressed air system) and helps the machines run smoothly.