Vacuum conductance
= Vacuum conductance
<Vacuum conductance> relates <gas> throughput to a <pressure> difference across a connection: $Q=C(p_1-p_2)$. For throughput in $\mathrm{Pa\,m^3\,s^{-1}}$, conductance $C$ has units $\mathrm{m^3\,s^{-1}}$, the same units as pumping speed.
For a pump of speed $S$ connected through a line of conductance $C$, a simple steady balance gives $1/S_{\mathrm{eff}}=1/S+1/C$. Thus a $100\,\mathrm{L\,s^{-1}}$ pump behind a $10\,\mathrm{L\,s^{-1}}$ connection supplies only about $9.1\,\mathrm{L\,s^{-1}}$ at the chamber. Conductance depends on geometry, <gas> and flow regime; the pressure-independent molecular-flow value should not be used indiscriminately in viscous flow.<Vacuum Technology for Ion Sources by Paolo Chiggiato>[Sections 2–3, conductance and effective pumping speed]{ref}