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.


Example
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
