Vacuum Pump Down Time Calculator
Estimate the time a vacuum pump takes to evacuate a chamber or vessel from its starting pressure to a target pressure, or the pumping speed needed to do it in a given time.
- t = V ÷ S × ln(P₀ ÷ P₁) = 2 ÷ 100 m³/h × ln(1,013 ÷ 10) = 5.542 min
Pump Down Equation
S = (V ÷ t) × ln(P₀ ÷ P₁)
V is the chamber volume, S the effective pumping speed at the chamber (assumed constant over the range), P₀ the start pressure and P₁ the target pressure, both absolute. The equation applies in the rough vacuum range where gas load from outgassing and leaks is small.
Worked example
A 2 m³ vessel pumped from 1013 mbar to 10 mbar with an effective 100 m³/h: t = 2 ÷ 100 × ln(101.3) × 60 = 5.5 min.
Frequently Asked Questions
What is effective pumping speed?
The speed actually available at the chamber, lower than the pump nameplate because pipes and valves restrict flow.
Why does the time rise at low pressure?
Pumping speed of many pumps falls near their ultimate pressure, and outgassing from surfaces adds gas load.
Does temperature matter?
Only slightly in the rough vacuum range; the equation assumes isothermal pumping.
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