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A Closer Look at Air Compressor’s Screw Element

If you are using a screw-type compressor, then you should know that the screw element is the most important part of your unit. It is where the compression takes place. It is like the heart or the center of your rotary screw air compressor, so to speak. The screw element of your compressor is also called air-end sometimes.

Why is this type of compressor popular? It is because they have this continuous process that supplies a steady and unchanging flow, with very minimal vibrations and also minimal need for maintenance work and a really long lifespan.


The screw elements can run 24 hours a day, seven days a week.  On average, your compressor’s screw element can work continuously for about 40,000 hours before requiring ay overhaul.

How Does It Work?

Basically, there are two screws or rotors inside the compressor element that turn in opposite directions. The air is ‘squeezed’ by an external force because the rotary screw compressor is also a positive displacement one. The rotors are specially designed for optimal efficiency as well as high performance. The rotors are often called ‘male’ and ‘female’.  The male rotor has lobes and is a lot thicker. The female rotor is thinner and has flutes or grooves. The male rotor usually has four lobes and the female has six grooves. Of course this may vary depending on the manufacturer as the industry is always looking for ways to improve screw design.

The way it works, air is sucked on one side, kept between the two rotors and then discharged on the opposite side. This kind of compression needs high power so it is usually supplied by huge electro motors.


Types of Screw Compressor Elements

There are two types of screw compressors, namely oil-injected and oil-free. The first one is the most common, perhaps because they are also the less expensive type. The latter is used in specific applications where it is absolutely necessary for the compressed air to be 100% oil-free. Examples of such application include chemical plants and food-processing plants, among others.

But what are the differences of the two types of screw compressor elements? And how come an oil-free element is more expensive than oil-injected?

The injected oil has various functions and among those is to seal gaps between the male and female rotors. These gaps or clearances allow compressed air to flow back to the wrong side lowering the efficiency of the unit. So it is important that they are sealed.

Since the oil-free type does not have any oil, the gaps between the rotors as well as the housing should be significantly smaller. That makes the price higher. In addition, they also require extra pockets for cooling water.


There you go folks! We hope this has given you some insight on how the screw element works for your compressed air system.



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