### 4.1.4 Compression ratio

The maximum pressure ratio between discharge pressure $p_{outlet}$ and intake pressure $p_{inlet}$ is referred to as the compression ratio

$K_0=\frac{p_{outlet}}{p_{inlet}}$

Formula 4-1: Compression ratio

In the case of blank-flanged inlet ports, the compression ratio (called $K_0$ due to zero delivery) is measured through gas intake on the outlet side provided that this is not expelled against constant atmospheric pressure.