Explain CCVM to me?

[Toxxyc]

Hi guys,

So I'm new, obviously. Well, new-ish. I'm on my second still and someone mentioned CCVM in my build thread. I've seen the name before and know it works with a coil thing at the top of the riser/column, but never paid attention to it because I'm building mostly a pot still (whisky and rum).

However, the option is there (albeit not for right now), so here I am, asking how the hell it works (might want something like that for making higher proof and cleaner neutrals soon). Out of pure boredom I Googled it last night, and as little as I knew how it worked, it confused me even more.

As I have it, and hear me out:

It's essentially a column with a T-piece at the top. The one part goes to the lyne arm and the last part straight up. The part going straight up gets a coil condenser that is lowered into the riser, and depending on how deep you let it drop into the riser, you can control the amount of reflux in the column. If you let the coil down deep enough so it covers the lyne arm part of the T-piece, you're essentially in full reflux. If you lift it so it covers part of the lyne arm part, you're in partial reflux and it you lift it up so the lyne arm piece is open, you're letting all vapour through and distilling "faster".

That I seem to understand OK. What gets me though is how does it contain the vapours? I know we NEVER close up a boiler, EVER, and there should always be an escape route for gas. Fine, my coil is always open on the far end of the still, but it seems with the CCVM you have the top of the column open as well? This is what confuses me. What stops your precious alcohol vapours from simply passing by the cooling coil and escaping out of the top of the riser? All the plans I've seen (and also the way Jesse on Still It does his), is simply "open" at the top. Again, my confusion - what stops the vapours from simply skipping the whole shebang and going straight up and out?