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Technology Background – Compressed Air

Air compressors use electrical energy to bring air to a high pressure. Most installed air compressor units use an electrical motor, while portable units generally use a petrol or diesel-driven motor.

There are two basic air compressors types, positive-displacement and dynamic.1

Positive displacement compressors

Positive displacement compressors operate by trapping a given quantity of air or gas in a compression chamber and mechanically reducing the volume which it occupies, causing a corresponding rise in pressure prior to discharge. At constant speed, the airflow remains essentially constant with variations in discharge pressure. Types of positive displacement compressors include reciprocating and rotary screw compressors.2
  • Reciprocating – Use a reciprocating piston to compress air into a storage tank through a valve. They can be a single or two stage system. ‘Reciprocating compressors are generally the most energy efficient compressors, both at full and part loads.’
  • Rotary screw – Consist of two meshing helical screws located within a casing which rotate in opposite directions to compress the air. They may be oil-injected or oil-free.

Dynamic compressors

Dynamic compressors impart velocity energy to continuously flowing air or gas by means of impellers rotating at very high speeds. The velocity energy is changed into pressure energy both by the impellers and the discharge volutes or diffusers. In the centrifugal-type dynamic compressors, the shape of the impeller blades determines the relationship between air flow and the pressure (or head) generated. Types of dynamic compressors include centrifugal air compressors.

  • Centrifugal – High-speed rotating impellers accelerate air and raise air pressure. Several impeller stages are required to reach the required operating pressures, and are oil-free. 3

For more information

The resources below provide more information on each of these types of compressors, including the advantages and disadvantages of different technologies and most suitable applications.

Footnotes ~ Show 3 footnotes

  1. Lawrence Berkeley National Laboratory (2003) Improving Compressed Air System Performance: A Sourcebook for Industry U.S. Department of Energy (Opens in a new window) 1.1 MB ↩
  2. Energy Efficiency Equipment Committee (2010) Improving the Energy Efficiency of Industrial Equipment (Opens in a new window) 3.8 MB ↩
  3. Energy Efficiency Equipment Committee (2010) Improving the Energy Efficiency of Industrial Equipment (Opens in a new window) 3.8 MB ↩