The pumping speed at a specified inlet is the gas throughput divided by the inlet pressure: . 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 through a line of vacuum conductance gives in the linear flow regime. Thus a large pump cannot compensate for an arbitrarily restrictive connection.[ref]
Vacuum Technology for Ion Sources by Paolo Chiggiato. Gas flow in molecular regime, pumping speed and effective pumping speed
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