Centrifugal ship s service air compressors were introduced into the fleet to meet this demand. The basic operating principles of the centrifugal air compressor are similar to those of a multistage centrifugal water pump, in that pressure of the air is increased as the air passes from one stage impeller to the next.
Air enters the compressor through a filter-silencer, where it undergoes an initial pressure drop.
The air then flows through an inlet nozzle to the first-stage impeller. This intercooler lowers the temperature of the air, increasing its density before it passes from stage to stage. Increasing the density of air requires fewer compression stages to raise the pressure of the air to the desired pressure of 125 psi. The compressed air passes through the second and third compression stages in a similar manner. After the compressed air leaves the third-stage compressor, it passes through a shell and tube type of aftercooler that uses seawater as the cooling medium.