Evacuation time

the time t required to evacuate a system
from an initial pressure P0 to a final presssure P1
is estimated with the following equation:

t = (V/S).Ln(P0/P1)

t: evacuation time [h]

V: system volume [m³]

S: average pump suction capacity [m³/h]

P0: initial pressure at t0

P1: final pressure at t1

N.B.: The equation is applicable for reasonably tight systems (neglecting a possible leakage and /or degassing), and when the pump suction capacity S is nearly constant over the entire operating range.


A 1000 m³ system must be evacuated from atmospheric pressure to 200 mbarA in 10mn.

S = (V/t).Ln(P0/P1)

S = (1000/10).Ln(1000/200)

S = 160 m³/mn

system volume, V = 1000 m³

evacuation time, t = 10 mn

initial pressure P0 = 1013 mbarA

final pressure P1 = 200 mbarA

required pump suction capacity, S = 160 m³/mn

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