It's a vacuum chamber. Old freezer compressor hooked up to suck. It'll suck about 26", but we just use it till about 18".
It'll hold a gallon jar, or a mixture of smaller ones. We use it to buy stuff in quantity and save it for future needs.
I've put normally canned goods in there, and the lids pop at about 7" +/- 2", so I think when we "preserve" a batch of beans or rice, or flour…… we can make it last.
You can even quickly marinate a piece of meat with it. No tricks.