= Pumping speed
{title2=$S$}
The <pumping speed> at a specified inlet is the <gas> throughput divided by the inlet <pressure>: $S=Q/p$. Its units are <volume (thermodynamics)> 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 $1/S_{\rm eff}=1/S_p+1/C$ in the <linear flow> regime. Thus a large pump cannot compensate for an arbitrarily restrictive connection.<Vacuum Technology for Ion Sources by Paolo Chiggiato>[Gas flow in molecular regime, pumping speed and effective pumping speed]{ref}
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