Blast gates - video

[Frank S]

Something like this is what I am talking about since it already has tight seals there will be no vacuum loss they can be bought in sizes ranging from 1 1/2" thought 3" openings. I haven't seen anything larger than that until you get into industrial quality valves.
Yes his craftsmanship is above reproach.

Inexpensive models have the simple pull handle, but you can buy these valves with 12V and air powered opening and closing attachments.