How Does A Rotary Screw Compressor Work?

Step by Step Guide to Increase the Pressure in an Air Compressor

A rotary compressor is a mechanical device that is used to generate and supply compressed air for various industrial applications. In general, its operation involves the gathering of normal air between its two meshed rotors and reducing the volume of this trapped air. The more detailed working of Rotary screw compressors is discussed in later sections of this text but before it’s important to understand some basics about rotary compressors. 

Rotary screw compressor is the latest type of air compressor available in the market. This air compressor brings a lot of benefits as compared to its formal type, piston air compressors. They are becoming very famous around the world due to the convenience they offer but at the same time they are a bit more expensive than older versions. There are two main types of rotary screw air compressors: Oil-injected compressors and Oil-free compressors. 

Oil-Injected Compressors

In oil-injected rotary air compressors, oil is used as a lubrication for the moving parts of the compressor. The lubrication helps the compressor to produce high-pressure gas in a single stage making the process fast and efficient. In technical terms, oil-based compressors offer high CFM and PSI repeatedly. 

The oil from the air is separated just before the air leaves the system and the separated oil is recycled to reuse for compressing the coming air. 

Oil-Free Compressors 

Oil-Free compressors are handy in industries where even a small content of oil can lead to quality degradation of the end product. They are more expensive than oil-based compressors as they require more mechanical work to produce the high-pressure air. Oil-Free compressors go through two levels of compression to deliver the required pressure compressed air. 

They are only used by the industries where it’s necessary to have oil-free compressed air, otherwise an oil-injected compressor is the first choice for everyone. For example, pharma companies, food manufacturers and medical oxygen plants prefer to use oil-free compressors. 

Rotary Screw Air Compressor
Rotary Screw Air Compressor

Working Principle Of Rotary Screw Compressor

In rotary screw compressors, there are two interlocking rotors contained in a sealed cavity. When the device is switched on, both the rotors rotate with high velocities. Now with the help of an opening valve the compressor sucks the air from the external environment. The rotating impellers trap the air from the valve and pass it to the cavities present between the rotors pair.

The air is then moved down to the chamber which has the functionality to decrease its size by moving away from the valve opening which results in a decrease in the volume of trapped air. As we know, a decrease in volume will lead to an increase in the pressure of the gas because the space for the air molecules has decreased. 

High-pressure gas will strike on the discharge valve of the compressor to allow its passage. As soon as the valve is opened the compressed air will be collected in some tank or container. Now, this compressed air is ready to be used for numerous purposes. 

Guide To Find The Right Screw Compressor For You 

Rotary screw compressors are available in a wide range of sizes. Knowing the required pressure, capacity and Horsepower of a compressor is necessary. These 3 factors are measured as:  


The pressure is measured in terms of pounds per square inch gauge(PSIG) OR kg/cm2g.


Capacity is calculated in cubic feet per meter(CFM) OR m3/min. It represents the volume of compressed air which the compressor can produce at a given pressure. 


Horsepower tells about the size of the motor used in a compressor.  


Rotary air compressors are in demand because they offer many advantages. They are designed to work continuously without any downtime. Also, they are easy to maintain, generate less noise as in canopy and are energy-efficient. So it’s worth giving them a chance. You must refer to our quick guide if you need assistance in choosing the right Rotary air compressor


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