A Complete Guide to Rotary Screw Air Compressors


When most people picture an air compressor, they think of a piston air compressor, also known as a reciprocating air compressor. These machines, which have been used for years, compress air by pushing it into a small space.

Rotary screw air compressors are an improved type of compressor that have many benefits over the more traditional models. Here is what you need to know about rotary screw air compressors, how they work, the different types, their pros and cons, and what you might want to consider when purchasing the right one for your needs. 

What Are Rotary Screw Air Compressors?

A rotary screw air compressor operates by using two meshed rotors to trap air, which reduces the air volume as it passes through the rotors. When the air is compressed into a lower volume, it can be used to inflate tires, power air tools, and for other useful applications. 

Different Types of Rotary Screw Air Compressors

A rotary screw air compressor can be oil-injected or oil-free. They can also be air-cooled or water-cooled. Oil-injected rotary screw air compressors use oil to seal and lubricate the rotors, whereas oil-free models are used in production, medical, and industrial applications where oil can’t contact the airflow. 

Air compressors create a lot of heat during operation, requiring cooling. About 80% of rotary screw air compressors are air-cooled, where a radiator/fan combination does the job. The other 20% are water-cooled, where a tuber-exchanger is used. 

Main Components of Rotary Screw Air Compressors

Here are the primary components you’ll find with rotary screw air compressors.


The “air-end” is the main component of this type of air compressor. It’s the compressed air system, with an inlet valve on one end and an outlet on the other. 

Air Filter

An air filter, mounted either remotely or directly to the compressor, is used to clean the compressor’s air

Primary Separator Tank

Oil-injected compressors need a primary separator tank to separate the air and oil at different stages of the process. 

Secondary Separation Filter

This filter will remove any remaining oil in the air that leaves the primary separation tank and put the oil back into the system. 

Oil Filter

An oil filter will gather any loose particles in the oil and prevent them from entering the air compressor. 

Oil Cooler

Because air compressors generate heat, an oil cooler can keep the compressor’s oil at the right temperature range for optimal performance. 


Hoses are required to move air and oil between various air compressor components. 


A rotary screw air compressor requires electrical or mechanical controls in the form of a switch, lever, or button for operation. 

How Rotary Screw Air Compressors Work

The various components just described work together to create compressed air that can be used for various purposes. Inside the compressors are a set of female and male rotors. The rotors are not alike, so the air becomes trapped between them when they are rotated in unison. 

The female rotor has concave cavities, and the male has convex lobes.

When the two come together without touching, it creates a compressive action. Also, the female rotor has slightly more lobes than the male, meaning it will rotate slower and is driven by the male rotor. 

When a rotary screw compressor operates, here is the step by step sequence.

  1. When the compressor is switched on, gas is pulled into the compressor chamber, and the two rotors begin to move.
  2. With the rotation of the impellers, the air is isolated and trapped in the cavity between the male and female rotors. 
  3. The air chamber gets smaller and moves away from the opening vale. The pressure inside the chamber increases as the volume decreases. 
  4. As the pressure goes up inside the machine, the air becomes condensed. 
  5. Once a certain pressure is reached, the compressor’s discharge valve will open, which allows the pressurized air to enter a receiver or holding tank. 

Note that if the air compressor is oil-injected, air mixed with oil will enter the process initially, and most of the oil is removed and recycled back into the pump at the end.  

Pros and Cons of Rotary Screw Air Compressors


Rotary screw air compressors have become the technology of choice across a wide range of applications. They offer businesses a long list of benefits.

  • Continuous operation — The machines do not need to be cycled on and off and are capable of continuous pressurization and airflow. 
  • Powerful performance — These compressors can perform at extreme temperatures and have high airflow rates, allowing them to operate in challenging conditions. This means they can operate heavy equipment and pneumatic tools efficiently and easily. 
  • Low noise — They are relatively quiet and small compared to other compressors, making them good options for point-of-use installations. 
  • Energy-efficient Compared to other models, these machines produce less heat and won’t lose capacity over time, making them cost and energy-efficient


Rotary screw air compressors may not be the ideal choice for everyone. There are a few disadvantages to this option.

  • Upfront cost — Rotary screw air compressors cost more upfront than reciprocating air compressors. But, these machines are more efficient and can last four times longer. 
  • Maintenance — These machines require regular servicing and skilled maintenance. But giving them the attention they deserve will extend their useful life.  

Rotary Screw Air Compressor Purchasing Considerations

If you plan to buy a rotary screw air compressor, here are some of the elements you’ll want to consider so that you get the right one for your needs.

  • Horsepower (HP) — You will need one HP of force to lift 550 lbs. one foot per second. 
  • Cubic Feet per Minute (CFM) — CFM refers to the volume of air that can pass through the pump in one minute. 
  • Pounds per Square Inch (PSI) — PSI measures the pressure that the air compressor can produce in a square inch of space. 
  • Electrical Phase — Air compressors can come in single-phase or three-phase devices. Three-phase electricity is most often found in industrial settings and single-phase in residential settings. 

C&B Equipment Sells and Services Rotary Screw Air Compressors

If you’d like to purchase a rotary screw air compressor or need service on your existing one, C&B Equipment can help. We are an industrial equipment and service company for pumps, air compressors, blowers, and related equipment. 

C&B Equipment can help you choose the best rotary screw air compressor to suit your needs and/or provide field service and repair support to keep your business running at peak productivity. Contact us today to learn more about our products and services.

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