More specifically, the head space is typically about 1/10th the volume of the whole keg. If you put 30psi into the head space and quickly disconnect, in about a day the equilized pressure in both the headspace and beer with be about 3 PSI. If you look at the charts, you'll quickly see why you can't practically do a single application of gas to reach say 2.5 volumes. A chart pressure of 13 psi would require a single burst of 130psi which is where your keg's pressure limit sits.
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