Basically, the vapors travel up the column and through the offset to the coil where they are cooled to a liquid and run back down the elbow. Then they either are drained out of the valve that is there, or the valve is left closed and it runs back (and with the help of a tongue soldered in)and is dripped back down the centre of the column.
The top is left open so no pressure can build and the cooling coil cools the vapors enough that none can escape. (most also put packing in the coil to ensure no vapor gets by)
So, there is no "bung" just a coil/packing to knock down the temp so the liquid runs back down either refluxing or being collected. With this setup you can go wide open on the cooling coil and keep the system in equalibrium until only the very highest %abv comes out. (theoretically 95.6% ABV)
That\'s my aim, to make/build a still that will get as close to the theoretical max as possible.
Some of the parts look like being a complete PITA though. It\'s not the easiest thing to find "needle valves". If I knew what kind of kit they\'re normally used in, I could probably track some down.
It\'s like, it\'s taken me a while to find somewhere that sells the larger bore copper pipe ( standard UK sizes being 15mm and 22mm ) but I think I\'ve found somewhere that does.
I though I might have a go at making different columns - I reckon that I can make a "vapour management" column quite easily, though it\'d depend on what size "gate valve" I can track down as to what size condenser I\'d build.
Then I\'d have to start looking around to see about the needle valves etc.
Of course, finding something to use as an appropriate vessel for a boiler is also proving to be a PITA - stainless beer kegs aren\'t easy to get hold of, the same applies to the stainless milk churns that have been mentioned.
I\'m certainly not gonna pay the kind of money that Brouwland want for a "wort heater"....