# Vacuum - Evacuation Time

## Vacuum pumps - calculating flow rate and required evacuation time

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 sealing's 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

### 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)

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