What Is A Screw Compressor?

Rotary screw compressors are a type of air compressor that get their name from the way in which they compress air. The air enters at the intake end and is trapped in the space between two very closely meshing helical screws, also known as rotors. As the space gets smaller and smaller, the air is increasingly compressed as it moves through the threads of the turning screws. This process is called positive displacement.

Screw compressor working principle; Left - View from Front and Top; Right - View from Bottom and Rear

According to the book Fundamentals of Natural Gas Processing by Arthur J. Kidnay, William R. Parrish (2006), in a dry-running rotary-screw compressor, timing gears ensure that the male and female rotors maintain precise alignment without contact which would produce rapid wear. In an oil-flooded rotary-screw compressor, lubricating oil bridges the space between the rotors, both providing a hydraulic seal and transferring mechanical energy between the rotors, allowing one rotor to be entirely driven by the other. Gas enters at the suction side and moves through the threads as the screws rotate. The meshing rotors force the gas through the compressor, and the gas exits at the end of the screws. The working area is the inter-lobe volume between the male and female rotors. It is larger at the intake end, and decreases along the length of the rotors until the exhaust port. This change in volume is the compression. The intake charge is drawn in at the end of the rotors in the large clearance between the male and female lobes. At the intake end the male lobe is much smaller than its female counterpart, but the relative sizes reverse proportions along the lengths of both rotors (the male becomes larger and the female smaller) until (tangential to the discharge port) the clearance space between each pair of lobes is much smaller. This reduction in volume causes compression of the charge before being presented to the output manifold.

5 Benefits Of Rotary Screw Compressors

As the technology of choice across a wide range of applications, screw compressors have a lot to offer customers:

  1. Continuous Operation: Capable of continuous airflow and pressurisation, they don’t need to be shut on and off and have no duty cycle. This means that they can operate continuously with little to no downtime.
  2. Easy Maintenance: With very little moving and contacting parts, wear and tear are minimised. Long service intervals drive down maintenance costs and make any routine checks and repairs quick, easy, and hassle-free.
  3. Powerful Performance: Screw compressors can operate in challenging conditions as they have high airflow rates and can perform at extreme temperatures. This means they can run pneumatic tools and heavy equipment easily and efficiently.
  4. Energy Efficient: Having stood the test of time, these durable machines produce less heat and conserve more energy than other models. These design features mean that they offer zero loss of capacity over time, keeping the lifetime cost of the compressor low.
  5. Low Noise Levels: Quiet operation is down to the small size of the units and the lack of moving parts, making them suitable for point of use installations.

This video by Atlas Copco illustrates the working of a rotary screw compressor brilliantly: