The calculator gives an engineering estimate only. Real systems add conductance losses, leakage and outgassing, so the result is optimistic; allow 1.3 to 1.5 times margin.
Pump-down time
Speed unit conversion
Formula and assumptions
The estimate uses a simplified isothermal model at constant pumping speed:
t = (V / S) x ln(P0 / P1)
- V: effective volume of chamber and piping, m3
- S: effective pumping speed in the target pressure band, converted to m3/s (nameplate m3/h divided by 3600)
- P0 / P1: start and target absolute pressure, mbar
Pumping speed falls noticeably as pressure approaches ultimate, so pulling from atmosphere to 10 mbar and from 10 mbar to 1 mbar cannot use the same S. Calculate in two stages for a closer result.
Typical ranges
| Pump type | Pumping speed | Typical working band |
|---|---|---|
| Single-stage oil-sealed rotary vane (V series) | from 20 m3/h, by model | atmosphere to 0.1 mbar |
| Roots booster (LC series) | 250 to 4200 m3/h | 30 to 0.01 mbar with backing pump |
The calculated speed is only a starting point. Flange size, pipe length and the number of bends cut the effective speed further. Send us the duty point and our engineers will check it against the actual piping.