Professional article
1) What pumping speed represents
Pumping speed, S, is the volumetric flow rate removed at the inlet. In vacuum practice it is stated in liters per second and links pressure and throughput using Q = P·S. This calculator turns measurements into comparable speed values for troubleshooting and sizing new vacuum lines.
2) Throughput method for steady gas load
Near steady state, gas load is expressed as throughput Q from leaks, permeation, or outgassing estimates. Dividing Q by the measured pressure P yields S. Example: 150 mbar·L/s at 0.5 mbar gives 300 L/s, matching the table.
3) Pressure decay method during pumpdown
Pumpdown data provides another route. For chamber volume V, pressure may fall roughly exponentially over a chosen interval. Using S = (V/t)·ln(P0/P1) gives the average speed. Choose P0 and P1 in one regime, and use t in seconds. A 50 L chamber dropping from 10 to 1 mbar in 120 s gives ~0.96 L/s.
4) Conductance limits real performance
High pump ratings do not guarantee high chamber speed. Tubing, valves, and traps introduce conductance limits, so the chamber sees Seff = 1/(1/S + 1/C). The smaller of S and C dominates. With S = 250 L/s and C = 80 L/s, Seff is about 60.6 L/s.
5) Unit handling and practical reporting
Vacuum work mixes Pa, mbar, and Torr for pressure, plus liters or cubic meters for volume. The calculator converts common units internally and reports both L/s and m³/s, helping produce consistent lab notes, acceptance checks, and service records across teams.
6) Interpreting results across regimes
Speed can vary with pressure because flow changes from viscous to transitional and molecular. Conductance often decreases sharply in molecular flow for long, narrow lines, while pump curves may also drop at higher pressures. Compare results in similar pressure ranges when benchmarking.
7) Accounting for leaks and outgassing
Real chambers often have continuous gas sources that set a pressure floor. The optional extra throughput field lets you add a known leak or outgassing contribution when applying S = Q/P, improving realism when pressures stabilize after initial pumpdown.
8) Good measurement practice
Record gauge type and placement, because readings near the pump can differ from chamber pressure. Note valve positions, line geometry, and temperature. Repeat calculations at more than one pressure point to spot conductance limits or unexpected gas loads. Exporting results supports traceability and reduces transcription errors during technical review.