Inlet pressure is the absolute pressure of air at the inlet of a compressor. The inlet pressure is always less than the discharge pressure.

Discharge pressure is the absolute pressure of air at the outlet of a compressor.

Compression ratio or Pressure ratio is the ratio of discharge pressure to the inlet pressure. Since the discharge pressure is always more than the inlet pressure, therefore the compression ratio is more than unity.

Compression ratio or Pressure ratio is the ratio of discharge pressure to the inlet pressure. Since the discharge pressure is always more than the inlet pressure, therefore the compression ratio is more than unity.

An axial flow compressor, in its simplest form, consists of a number of rotating blade rows fixed to a rotating drum. The drum rotates inside and air tight casing to which are fixed stator blade rows. The blades are made of aerofoil section to reduce the loss caused by turbulence and boundary separation. As the drum rotates, the air flows through the alternately arranged stator and rotor. The flow of air is parallel to the axis of compressor.

In an axial flow compressor, the ratio of pressure in the rotor blades to the pressure rise in the compressor in one stage is known as degree of reaction. The type of rotary compressor used in gas turbines, is of axial flow type.