The volumetric flow rate into a pump inlet, S, in L/s or m³/h, measured at the inlet flange with standard test-dome methods. It varies with pressure and gas type: a turbo rated for nitrogen pumps hydrogen more slowly, and a rotary vane pump's speed collapses as it nears its ultimate pressure. The amount of gas removed is speed times pressure, so a pump with constant speed removes less and less gas as the pressure falls.
Rotary vane is 16 cubic metres an hour on paper, but its pumping speed down near 1E-2 is a fraction of that.
Also heard as
- speed
- S
- volume flow rate
Related terms
Effective pumping speed
The pumping speed actually delivered at the chamber after losses in the connecting pipes and valves.
Throughput
How much gas flows past a point each second, counted as pressure times volume, in units such as mbar·L/s.
Conductance
How easily a pipe, orifice or valve lets gas through, expressed in litres per second.
Ultimate pressure
The lowest pressure a pump can reach on a sealed, clean test dome, as stated on its data sheet.