VM still output rate ALC verses Water

[Yummyrum]

Well if you’re like me , you’ve probably read more than a few times that a VM still will slow down towards the end and that this is due to Alc vapour being heavier than water and therefore that at the branch , or Tee , the water will not want to fall down hill into the condenser.

Now that part has always intrigued me . Surely , a Vapour Management still simply splits vapour regardless of its constituents , ….. it is proportioned dependant on the physical size of the port verses the column diameter .


Well its test time .

This is part one .
I am going to compare a typical 30%ABV charge to plain water in my VM and see what happens .

So first off , i want to see in Pot still mode how much vapour the boiler is creating from a 30% ABV charge .

I have removed the RC and capped the top . The VM valve is held wide open with a cable tie so no accidents .

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Once up to temp and drawn off about 300mls

take off rate (averaged over three readings ) is pretty damn close to 7l/hr ( thats a 2400w element )

OK ,now I slip the RC in the top , ball valve is still wide open …. Theoretically a 1:1 reflux ratio as I have a ball valve that equals the reducer Tee .
Poured all the collection from previous run back to boiler so same charge again.

Measured output is 3.56 l/h ( again , average of three samples) ….. surprisingly pretty close to the 1:1 theoretical . …. That totally surprised me


Now the water run .

Pot still mode .

Collection rate was so close to 3l/h …. I’m calling it that .

Clearly , it takes more effort to boil water than Alcohol . So , the amount if vapour produced is less . …. Less than half that of Alcohol . And this also verifies why we see a gradual decline in takeoff rate as a run progresses .

Now the reflux mode .
Again , same setup as the first alcohol test with the valve fully open .

So based on what I got from the Alcohol run I would have predicted close to 1.5l/h .

Interestingly , the take off was 695ml/h …. I’ll call it 700ml/h .


This turned out to be less than half of what I expected .

There does indeed seem to be less output from a VM when only water is in the boiler . It does not stop . … but it’s less .

The big question in my mind is , is it due to the gravity thing or something else :confusion-shrug:

If the split vapour out the tee went UP into a PC instead if down into a PC …. Will that change things ?
That is what I want to investigate next .

In summary from todays experiment:

Alcohol …7000ml/h in pot mode …… 3560ml/h valve wide open .
Water …..3000ml/h in pot mode ….… 700ml/h valve wide open .