Vacuum - 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

• 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.

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Estimated Evacuation Time to Reach 500 Micron Vacuum - 6 feet pipe

Temperature ^oC
K
^oF

Length m
km
in
ft
yards
miles
naut miles

Area m²
km²
in²
ft²
miles²
acres

Volume m³
liters
in³
ft³
us gal

Weight kg_f
N
lbf

Velocity m/s
km/h
ft/min
ft/s
mph
knots

Pressure Pa
bar
mm H₂O
kg/cm²
psi
inches H₂O

Flow m³/s
m³/h
US gpm
cfm