### 4.1.2 Pumping speed and throughput

The pumping speed $S_0=\frac{dV}{dt}$

(Formula 1-17) is the mean volume flow through the cross section of
the inlet port of a vacuum pump. In diagrams the volumetric flow rate
or pumping speed is displayed on the Y axis versus the inlet pressure
on the X axis. The maximum pumping speed which a pump can achieve due
to its geometry is referred to as its rated pumping speed.
Determination of the pumping speed is described in basic standard ISO
21360-1: 2012. Pumping speed is indicated in m^{3}
· s^{-1}. The units of m³ · h^{-1},
l · s^{-1} and l · min^{-1} are also
customary.

The throughput $q_{pV}=S \cdot p=\frac{dV}{dt} \cdot p$

(Formula 1-16) denotes the gas throughput in a vacuum pump as a
function of inlet pressure. It is expressed in Pa · m^{3}
· s^{-1} or hPa · l · s^{-1} =
mbar · l · s^{-1}. In the case of pumping
stations that consist of gas-displacement pumps, all pumps connected
in series have an identical throughput.