Pumping speed ($S$)

The pumping speed at a specified inlet is the gas throughput divided by the inlet pressure: $S=Q/p$. Its units are volume per time, commonly litres per second. A pump's speed depends on gas species and operating conditions.

Connecting a pump of speed $S_p$ through a line of vacuum conductance $C$ gives $1/S_{\mathrm{eff}}=1/S_p+1/C$ in the linear flow regime. Thus a large pump cannot compensate for an arbitrarily restrictive connection.^[ref]