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Engineering ToolBox > Vacuum - Required Evacuation Time

Calculating flow rate and evacuation time of vacuum pumps

The evacuation time for a vacuum pump can be calculated as

t = V/q ln(p₀/p₁) (1)

where

t = evacuation time (s)

V = enclosed evacuated volume (m³, cu ft)

q = volume flow rate capacity of the vacuum pump (m³/s, cu ft/s)

p₀ = initialization pressure - normal atmospheric pressure (mbar, mmHg)

p₁ = end vacuum pressure (mbar, mmHg)

Note! Leakage through sealings etc. should be compensated by adjusting the volume flow rate of the vacuum pump.

(1) can be simplified to

t = V/q N (2)

where

N = natural log constant for the actual vacuum

N = 1 for vacuum up to 15 in Hg gauge

N = 2 for vacuum up to 22.5 in Hg gauge

N = 3 for vacuum up to 26 in Hg gauge

N = 4 for vacuum up to 28 in Hg gauge

• Vacuum in torr, mm Mercury, psi and kPa

Example - Vacuum Evacuation Time

Evacuation time of 1 m³ volume, evacuated to 500 mbar abs - vacuum pump volume flow capacity 0.1 m³/s - can be calculated as:

t = 1 (m³)/0.1 (m³/s) ln(1000 (mbar)/500 (mbar))

= 6.9 s

Evacuation to 100 mbar abs:

t = 1 (m³)/0.1 (m³/s) ln(1000 (mbar)/100 (mbar))

= 23 s

Evacuation to 10 mbar abs:

t = 1 (m³)/0.1 (m³/s) ln(1000 (mbar)/10 (mbar))

= 46 s

Vacuum Evacuation Time Calculator

The calculator below can be used to calculate the vacuum evacuation time.

V - enclosed volume (m³, cu ft)

q - volume flow rate capacity (m³/s, cu ft/s)

p0 - initial pressure (mbar, mmHg)

p1 - final pressure (mbar, mmHg)