The primary purpose of vacuuming out a column, is to remove the oxygen, so that when we inject the LPG, it doesn't produce an explosive mixture.
What you have is a column with valves on each end, which begs the question as to how are you going to introduce the LPG into the column after vacuuming it out, without introducing atmosphere?
Which brings us to the next issue, which is, after you've flooded the column, how are you going to remove the LPG/essential oil mixture from your column without producing an explosive atmosphere?
And moving on to the last issue with a simple valved column. Sweet Mary's charms are concentrated in her trichomes, which are on the outside of the flowers and leaves. There is nothing inside the plant material that we covet, nor do we covet the non polar protective plant waxes coating the plant material.
The fastest way to dissolve the trichomes without dissolving the plant waxes, and subsequently the longer chained non polar molecules like C40 b-Carotene, and C55 Pheophytin, is fully wet the material and use flow to keep the LPG, trichomes boundary layers from stagnating.
Because both LPG and those waxes/longer chained molecules are non polar, that is best done below -30/50C, to slow down their absorption rate while the trichome heads are dissolved.
We've found that it takes around three (3) column volumes of LPG to reach the point of diminishing returns dissolving the trichomes using flow. Your design should include how you are going to put three volumes through your column without creating an explosive mixture.
Here is a link to a simple passive extraction and reclaim system:
https://web.archive.org/web/20160303074119/https://skunkpharmresearch.com/passive-butane-extractor-and-reclaimer/
The lower tank gives you room for the extra LPG, and if you invert it, it will re flood the column using the LPG mixture in the lower tank.
Note that it uses a LPG supply tank connected using a hose, and the entire system, including the hoses are vacuumed out, before using the tank valve to flood the column.