Almost ready to start appreciate assistance

[Fourway]

why does the vapor prefer the skinny side detour over the big wide straight highway to freedom guarded by a perfectly innocent looking coil full of cold water? I mean clearly it works and my natural sense of physics is failing me here... to me it looks like it would just run at 100% reflux all the time... vapor would go up past the side corridor and reflux would fall down past it.

[Dnderhead]

The vapor tends to take the path of least resistance.

[theholymackerel]

I'm not liscensed on those types of stills, but my Wild-Ass-Guess would be that the distillate arm works like a syphon and the condenser on the end of it makes for a low pressure zone.

[Fourway]

The vapor tends to take the path of least resistance.

fat pipes offer less resistance than skinny pipes don't they?

I'm not liscensed on those types of stills, but my Wild-Ass-Guess would be that the distillate arm works like a syphon and the condenser on the end of it makes for a low pressure zone.

By that logic (and it seems like good logic) shouldn't the coil condenser above be creating low pressure too? perhaps more?

[Dnderhead]

Yes, but you whould have to balance with reflux, if you have time/money you could do some experiments.
(if to big you whould reduce reflux/ too small and to slow take off)

[Fourway]

Yes, but you whould have to balance with reflux, if you have time/money you could do some experiments.
(if to big you whould reduce reflux/ too small and to slow take off)

no help...
Its the physics of this I'm not getting.
how can you control reflux?

[Hawke]

In this type of still, you need to look at the vapor as a gas. It will fill all available space in the container. The slight pressure differance created between the takeoff port and reflux condencer is enough to push vapor into the port once the takeoff valve is opened. VM has a fairly high reflux ratio, but is controled by takeoff rate.

[Fourway]

In this type of still, you need to look at the vapor as a gas. It will fill all available space in the container. The slight pressure differance created between the takeoff port and reflux condencer is enough to push vapor into the port once the takeoff valve is opened. VM has a fairly high reflux ratio, but is controled by takeoff rate.

I don't understand why there would be any pressure difference at all... if anything shouldn't the pressure going down a long skinny tube be greater than the pressure going up a short wide tube?

[Mud]

Hey Fourway and Holy Mack,
There's been a bunch of recent threads about how VM works. Minime has one with plenty of info including a lot of experimentation and discussion on stream splitting here.

Might be worth a little reading if you're interested.

-Mud

[HookLine]

why does the vapor prefer the skinny side detour over the big wide straight highway to freedom guarded by a perfectly innocent looking coil full of cold water? I mean clearly it works and my natural sense of physics is failing me here... to me it looks like it would just run at 100% reflux all the time... vapor would go up past the side corridor and reflux would fall down past it.

It prefers the downward pointing take-off arm because high strength ethanol vapour (above about 47%, I think) is heavier than air, so it wants to sink. This is why the output from a VM column will stop when the vapour at the head falls to below that concentration. It is also why you cannot fully test the operation of a VM with plain water, because water steam is lighter than air and always wants to rise.

In this type of still, you need to look at the vapor as a gas. It will fill all available space in the container. The slight pressure differance created between the takeoff port and reflux condencer is enough to push vapor into the port once the takeoff valve is opened. VM has a fairly high reflux ratio, but is controled by takeoff rate.

VM does not have an inherently high (minimum) reflux ratio, that is determined by the ratio of column cross-sectional-area (at the take-off port) to take-off port CSA. If they are equal, then the minimum ratio is 1:1.

You can increase the output rate by creating more pressure differential, but that is not the main principle of a VM still. That pressure differential can be increased by increasing resistance to vapour flow into the reflux condenser section, or (to a lesser extent) by increasing the height of the vertical drop above the product condenser (ie increasing the chimney/siphon effect).

If the column to take-off port CSA ratio is low (less than maybe 2.5:1) then your maximum take-off rate will be above your take-off rate for premium product anyway, so in practice you do not need to be able to get the minimum reflux ratio below that for a VM head.

It is all about choosing the right column to take-off port ratio.

[trthskr4]

Is any space between the takeoff point and upward to the reflux condenser wasted space then? I mean there needs to be a little room or at least the reflux condensers lowest point and the highest point of the takeoff port need to have a minimal space correct? Just trying to get my head wrapped around this too.

[HookLine]

Is any space between the takeoff point and upward to the reflux condenser wasted space then? I mean there needs to be a little room or at least the reflux condensers lowest point and the highest point of the takeoff port need to have a minimal space correct? Just trying to get my head wrapped around this too.

Not sure. IIRC some have argued that there does need to be an inch or two between the bottom of the reflux condenser and the top of the take-off port, so that the collapsing vapour at the condenser doesn't interfere with the vapour stream splitting at the take-off port.

[Fourway]

wait a minute... the top of the column isn't sealed is it?

[trthskr4]

Nope, not on a VM. Gotta have a vent hole above the condensor.

[HookLine]

Nope, not on a VM. Gotta have a vent hole above the condensor.

Or a reliable pressure relief doo-hicky.

Could be as simple as a cork in a hole.

[Fourway]

Nope, not on a VM. Gotta have a vent hole above the condensor.

ok... thats a relief.

I'm still flummoxed... but I'll accept that I can't understand everything and leave it.

I am perplexed by the fact that we are calling it a VM though...
doesn't it have it's own name?
Why does it co-opt the overarching name of an entire subclass of head designs as its own name?
Isn't a Nixon-Stone or a Boka-Slant plate head a type of VM?

Isn't that a bit confusing?

[Fourway]

Or a reliable pressure relief doo-hicky.

Could be as simple as a cork in a hole.

You're joking right?

[GingerBreadMan]

Heh, I have a still without a hole at the top that can operate in VM mode -



More info on the build here -

http://homedistiller.org/forum/viewtopi ... =17&t=6900

The hole at the top is a safety feature, but doesn't matter in theory. My still is completely open (there is no valve at the output).

By controlling the power and cooling I can put this still into reflux mode. Despite the short column at any time I can get 92% ABV output at any time - if I want. I speculate if my column was 2" instead of 1 1/2" and maybe twice as high I could get 94% ABV out of it. Taller, wider, I could get even more.

To answer your questions as how this works - it's pure magic! Well not so. Think about this. If the condenser at the top is capable of knocking down all vapors then it's going to liquify all the vapors and it will drip down the packing. At some point equilibrium will happen. That is to say there will be no output of distillate.

However, imagine a ballon filled with air, put a pin hole in the balloon and air will release, no?

So despite thinking that no vapor will ever exit the hole on the side, that is not true, some vapor will no matter what you do, it's just going to happen, just like the balloon.

Good news is, that since it's at the top of the column which is in equilibrium, it is that most concentrated ABV that it can be.

Hope this makes sense.

[HookLine]

Isn't a Nixon-Stone or a Boka-Slant plate head a type of VM?

No, they are liquid management. The difference between LM and VM is in which phase state the reflux return/product take-off ratio is decided, liquid or vapour. In LM it is determined by splitting the liquid condensate into reflux return and product take-off streams. In VM that split occurs during the vapour phase, before it hits the reflux or product condensers and is condensed to liquid.

[Mud]

We don't spoonfeed around here sir. You need to read, read, read. Tater has some good sites in his signature.
http://homedistiller.org/forum/viewtopi ... =17&t=6151

[GingerBreadMan]

Heh, that's just so low.

There's some fascinating stuff I've learned over that last 6 months that just blows away all theory posted here.

[rad14701]

Heh, that's just so low.

There's some fascinating stuff I've learned over that last 6 months that just blows away all theory posted here.

Several members have been working hard to move the understanding of VM forward... Snuffy and Minime have tinkered like mad scientists... A good summary of everyones efforts would be beneficial in helping explain the how and why...

[alkoholics]

wow i didn't think this thread would get that far buy the time i started reading tonight, well guess its time to start the reading.

[alkoholics]

oh ya and i messaged the person who first posted this and maybe they will jump in for those haveing issues.

[HookLine]

Or a reliable pressure relief doo-hicky.

Could be as simple as a cork in a hole.

You're joking right?

Nope. Seen a cork used quite a few times by folks here to plug a hole, often in the thermo port with a small hole in the cork to stick the thermometer through. No different in principle from just sitting a cap on top of a pot column and sealing it with a touch of flour paste.

It is the 'weakest link' principle. Make sure it can blow long before the rest of the still can.

The pressure inside a still (at least the ones we use) is minimal to start with, so the blow out pressure only needs to be maybe 2-3 psi, which is way less than the max safe pressure a beer keg can take (about 70 psi).

[Mud]

We don't spoonfeed around here sir. You need to read, read, read. Tater has some good sites in his signature. ...

That was meant as a joke, Fourway. Sorry if you took offense.

-Mud

[Fourway]

We don't spoonfeed around here sir. You need to read, read, read. Tater has some good sites in his signature. ...

That was meant as a joke, Fourway. Sorry if you took offense.

-Mud

I nearly fell outta my chair laughing.
I deserved it too hijacking a novice thread to trot out my ignorance and inability to learn anything new.

[maoule]

[Tatt2d]

Heh, I have a still without a hole at the top that can operate in VM mode -

The hole at the top is a safety feature, but doesn't matter in theory. My still is completely open (there is no valve at the output).

By controlling the power and cooling I can put this still into reflux mode. Despite the short column at any time I can get 92% ABV output at any time - if I want. I speculate if my column was 2" instead of 1 1/2" and maybe twice as high I could get 94% ABV out of it. Taller, wider, I could get even more.

If I'm not mistaken isn't this a CM (cooling management) rig. That s what i have also and I have to balance both the heat input as well as the cooling flow/temp to regulate reflux and output rate. Keeps you busy and on your toes..

As for the "how it works" question, the scientific answer is PFM.

Check this stickie out also - helped me understannd alot VM vs.LM vs.CM

[alkoholics]

thanx for all the great tips everyone, well im going to start a new thread on the build since this one is getting a bit interesting to have build pics in, im almost there.