Reduced take off section on VM stills

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PLAYMP
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Reduced take off section on VM stills

Post by PLAYMP »

I'm conceptualizing a design for a future VM build (not CCVM, but I don't think that matters here). Most designs I've seen include a 3'' or 2'' packed column, but reduced take-off and condenser sections (2'' column with a 1'' valve and 1' liebig condenser, for example). What is the rationale for this? Is it cost/availability of materials? cost to run? or is there another functional benefit to the reduction? I could see the reduction creating more pressure to guide the vapor through the condenser, but am unsure if that's a thing.

I ask because I have access to a large 2'' gate valve that I could re-use for larger builds down the road and was wondering if I could just keep everything at 2'', including 2'' shotgun condenser. I'm attaching an image of my design, any thoughts or feedback are welcome.
2'' design.PNG
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Re: Reduced take off section on VM stills

Post by still_stirrin »

OK, so a smaller diameter VM takeoff compared to the column diameter will affect the minimum reflux ratio you can achieve with the split. However, because the reflux ratio (R) is the ratio of vapor condensed back down the column (L) to the vapor that is advanced to the product condenser (D), or shown R=L/D, as the vapor valve is closed, the reflux ratio increases to the extreme when the valve is closed that the reflux ratio is infinite. Similarly, in a potstill where all of the vapor produced advances to the product condenser, then the reflux ratio zero.

This gives an indication to one advantage of a large diameter vapor valve, namely a “minimum reflux ratio” capability. Also, with a large valve and vapor piping system, the vapor flow velocity will be slower and more “laminar”, maintaining a uniform flow rate.

However, the cost of piping and valves definitely affects design options because a 2” gate or ball valve are significantly more expensive than a 1” valve. So, economics is definitely a factor.

My reflux column is a conventional VM valve (with a combination liquid regulated output too). The valve is 1” full opening. But my reflux condenser is a concentric with a concentric liquid cup (for the LM operation) which is fed through a 1” ID throat from the 2” column. Calculating the minimum ratio would be 1:1 if the LM valve was fully opened, as the vapor produced would be equally split between the VM valve and the throat to the reflux condenser. However, I NEVER run my reflux column this way. I use it for high purity (high reflux ratio) distillation only. As a result, rarely do I have the valve opening more than 1/4 open.

Summarizing, you don’t NEED a full 2” valve in a 2” column to run in reflux operations. It is expensive and if you’re goal is high purity, you’ll likely only have the valve cracked open.

But, if you want a low, or minimum reflux ratio, ie - R=0 or R=1, then, just make your still modular so you can remove the reflux column and head and replace it with a short riser and a potstill head. That’s the way I do it...”the right tool for the job”.
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Re: Reduced take off section on VM stills

Post by bluefish_dist »

The reason for reduced sections is simply cost. Large valves are expensive. Also there is no reason to have large valves as the velocity at the takeoff point is not critical. My first build was a 2 cups design with a 2” necked down to 1” for takeoff, then back up to 2” for the condenser. It allowed a 1” valve for a 1:1 reflux and a little cheaper cost.

Now my still heads are a different design for lower height and less fabrication. But they still neck down either from 4” to 2” or 6” to 4”. Saves on cost of components.
A61C59EE-6247-462C-90BB-B07988846218.jpeg
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Re: Reduced take off section on VM stills

Post by PLAYMP »

Thank you for the detailed and informative responses. It sounds like my large take-off and valve isn't going to hurt anything, but is probably overkill.

Truthfully, the large valve gives me some motivation to one day build something that actually needs it :lol: . But then again, I can settle for a 1 inch valve and reinvest the savings in more copper parts, or a gin basket or something. Lots to think about...
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Re: Reduced take off section on VM stills

Post by kimbodious »

Have you considered the no valve CCVM design?
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Re: Reduced take off section on VM stills

Post by PLAYMP »

I have looked up on the CCVM, I just have access to ss valves via a family friend so I figured I might as well incorporate them.
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Re: Reduced take off section on VM stills

Post by Tummydoc »

Unless access means FREE, lose the valve and go CCVM.
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Re: Reduced take off section on VM stills

Post by Yummyrum »

So you want to use this still for stripping ?
If yes ... then do consider a CCVM

Do you want to use this still for Neutral ?
If yes then consider that to make a Neutral , you will be running with a very high reflux ratio .
That means that your big arse expensive ( or maybe not ) valve will in reality be barely cracked open .
It will be very touchy to set and adjust .

Using a smaller valve will give a wider usable operating range and therefore be easier to adjust .
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Re: Reduced take off section on VM stills

Post by bluefish_dist »

Yummyrum wrote: Mon Nov 30, 2020 3:54 am So you want to use this still for stripping ?
If yes ... then do consider a CCVM

Do you want to use this still for Neutral ?
If yes then consider that to make a Neutral , you will be running with a very high reflux ratio .
That means that your big arse expensive ( or maybe not ) valve will in reality be barely cracked open .
It will be very touchy to set and adjust .

Using a smaller valve will give a wider usable operating range and therefore be easier to adjust .
Very true. On my 6” vodka column I ran a 2” valve and it was never more than half open.
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Re: Reduced take off section on VM stills

Post by Oatmeal »

bluefish_dist wrote: Sun Nov 29, 2020 10:42 am there is no reason to have large valves as the velocity at the takeoff point is not critical.
A61C59EE-6247-462C-90BB-B07988846218.jpeg
What are the practical limitations of reducing a large diameter column in a vm system for the valve? Is 1" too small for a 4 " column for example? What effects does this reduction have?

I guess the larger take of a ccvm is to allow some control with the coil, while with a vm the vapor path can be controlled by the valve, so take of size is less important?

Is their a speed difference between a vm and a ccvm? I feel that greater reflux ration are slower but "higher quality"?
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Re: Reduced take off section on VM stills

Post by Yummyrum »

I have 1.25@ on my 4” . Its still not near open when doing a Neutral .However, when using the same head above 4 plates for Rum , it’s pretty much wide open .

So For Neutral , I’d say for sure you could use 1” takeoff on a 4” column .
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Re: Reduced take off section on VM stills

Post by bluefish_dist »

I often ran a1” valve on a 4” column when making neutrals. No need for a large valve. Even when I ran flavored, I usually only ran a 3” on a 6” column. Even then it was less than half open for most of the run. Being able to do 1:1 reflux imho is not needed for most stills.
Last edited by bluefish_dist on Fri Nov 26, 2021 6:42 am, edited 1 time in total.
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Re: Reduced take off section on VM stills

Post by Oatmeal »

You generally shoot for a 4 to 1 ratio, no?

I guess even ccvm's are generally not run at 1:1, but are designed to be able to. For what good? Designing for a narrower reflux range seems more liberating from a build perspective, like keeping the vapor path 2" to the pc (instead of using a reducer in a 3" ccvm context).

My question was more related to the theoretical minimum functional vapor path for a vm. Could the whole column (let's say 3") be constricted down to 1 " with a t for the take off, and the be resized back to 3 for condensing? A faster vapor speed might make the valve more responsive? Possible "choking" or entrainment at this, sigh, "vapor choke-point"...
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Re: Reduced take off section on VM stills

Post by Yummyrum »

Oatmeal wrote: Thu Nov 25, 2021 6:20 pm . Could the whole column (let's say 3") be constricted down to 1 " with a t for the take off, and the be resized back to 3 for condensing?
Do you mean like this ?
OK , not 3” reduced to 1 “ , but you get the idea .
6AE31CDE-3D87-4158-B77C-1D0F53E55EF0.jpeg
1C617B43-D407-43FE-A8D4-2CA0F7FFC688.jpeg
1C617B43-D407-43FE-A8D4-2CA0F7FFC688.jpeg (31.6 KiB) Viewed 694 times
Iff’n so then you raise a good question . The reducer T section thingy works well for me . But I guess you could be correct that with too much reduction , the vapour split might not happen so well .
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Re: Reduced take off section on VM stills

Post by Oatmeal »

Hmmmmmm. According to Hookline's still drawings I'm contemplating (and you run) an all in one Nixon-McCaw vm head. Probably time to bite the bullet and get the compleat distiller and Riku's book....

Looks like an external condensate return on your head?

Thanks for the pics!
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Re: Reduced take off section on VM stills

Post by Yummyrum »

Oatmeal wrote: Fri Nov 26, 2021 7:04 am Looks like an external condensate return on your head?
Correct , at the time I thought I migjt like to play with reverse liquid management (RLM) but have never bothered , butbthat was the main reason it was made external
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