Air compressors are driven by electric motors imparting kinetic energy to air and then kinetic energy is converted to pressure energy. Compressors are used to compress air by decreasing volume and imparting a corresponding increase in pressure. 


Different compressors are used onboard for different purpose:

  1. Refrigeration compressors - Air conditioning and refrigeration

  2. Supply of compressed air 

  3. Engine turbochargers - The engine needs compressed air for compression. 

  4. Control air compressor for supplying control air.

  5. Topping air compressors for topping up and taking into account of the leakage air.

  6. Deck air compressor.

  7. Oil-free compressor for filling breathing air compressor


On board the ships compressed air is used for a variety of uses as given below:


  1. For automation and control of main and auxiliary machinery and equipment.

  2. Starting of main engine, auxiliary engine and emergency generator.

  3. For pressurizing the hydrophore system for domestic fresh water and sanitary system.

  4. Using a sewage plant for conducting aerobic sewage breakdowns.

  5. Soot blowing operation of boiler

  6. Used in fog horns and ship whistles.

  7. For heaving the lifeboat up using an air motor.

  8. Used in pneumatic pumps and hand tools (grinders, drill, spanner, jacks, chisel)

  9. General service air for cleaning and painting.


Two pressures are generally used onboard:

High pressure - 30 bar

Low  pressure - 7 bar 

For high-pressure reciprocating compressors are used. Double stages are provided to increase efficiency and done using inter and after cooling. The compression ratio of 1:7 is common.