How Does LM Compress Heads Better?

[Salt Must Flow]

I feel like I have to be missing something or maybe I'm misunderstanding. I keep searching and reading everything I can find. I keep finding statements like, "LM has very good heads compression (probably the best of the three main design types)". People keep saying, "LM is great for heads compression", " LM is exceptional at compressing heads", but I haven't found a single explanation as to how/why.

I understand that LM collects what condensates directly from the reflux condenser. I understand that the take-off rate is variable. I understand that any excess reflux overflows the collector and falls onto the packing. So exactly what about this makes it better at compressing heads?

Just for clarity, I know what compression is. For instance with my still, tails is held back very very well. Suddenly I'll see the vapor temp rise and tails comes right away. So if we are to define our terms, that's an example what I believe "compression" is. I just can't fathom how LM "compresses heads". It just doesn't make any sense to me at all.

The only explanation I can think of is that people are taking off 100% of the reflux which is specifically something other still designs cannot do. Other still designs can do a similar thing by allowing 100% of the rising vapor to leave the still (after stabilizing), condense it and collect it. So in this case there's really no difference. What am I missing? Is this just a myth, old outdated info?

[bunny]

i don't think LM is better at compressing heads.
Your reflux column does the actual stacking of your distillate.
I do believe it's easier to operate do to the extra fine control of take off speed in LM.
You can takeoff slow enough to avoid taking off as much hearts or even tails as you might using faster take off of other methods.
Yes, LM is slower, but that's the tradeoff.

[elbono]

I'm no expert but I agree, reflux in the column is doing the "compression". LM vs VM vs CM is just the control mechanism for how much reflux or takeoff is happening.

The one exception is a VM, it "compresses" tails better. Actually it has difficulty producing tails at all. The first hint I found about this was in the cleaning instructions where I found:
"Special consideration for VM: you might struggle to get steam out the takeoff" I did and followed the instructions but it made me think, why?. The second hint is in Ian Smiley's book about making pure corn whiskey. In his procedure he states "an LM can pull this trick but a VM can't" when you're collecting toward the end of the run again made me think why?

Contrary to my initial assumption water vapor is less dense than air and alcohol vapor is more dense than air. With a LM or CM there is only one vapor path so the vapor follows it, in a VM the vapor comes to a point where it can go two directions, up or sideways. If the vapor has less water content it is more dense (heads and hearts) it wants to go down but will take sideways as the best alternative, if it has more water content it is less dense (tails) it wants to go up, gets refluxed and little goes out sideways. At the end of a run my CCVM slows down a lot which makes me think this description is correct.

I've said if before I'm a newb, please don't hesitate to point out my misconceptions. I'm here to learn. More experienced opinions are wanted.

[elbono]

Yes, LM is slower, but that's the tradeoff.

I've seen that over and over and don't understand it. If all the condensate from the RC gets collected and either overflows back down the column or goes out the collection port isn't max collection rate a matter of the size of the output plumbing?

[Salt Must Flow]

I'm no expert but I agree, reflux in the column is doing the "compression". LM vs VM vs CM is just the control mechanism for how much reflux or takeoff is happening.

The one exception is a VM, it "compresses" tails better. Actually it has difficulty producing tails at all. The first hint I found about this was in the cleaning instructions where I found:
"Special consideration for VM: you might struggle to get steam out the takeoff" I did and followed the instructions but it made me think, why?. The second hint is in Ian Smiley's book about making pure corn whiskey. In his procedure he states "an LM can pull this trick but a VM can't" when you're collecting toward the end of the run again made me think why?

Contrary to my initial assumption water vapor is less dense than air and alcohol vapor is more dense than air. With a LM or CM there is only one vapor path so the vapor follows it, in a VM the vapor comes to a point where it can go two directions, up or sideways. If the vapor has less water content it is more dense (heads and hearts) it wants to go down but will take sideways as the best alternative, if it has more water content it is less dense (tails) it wants to go up, gets refluxed and little goes out sideways. At the end of a run my CCVM slows down a lot which makes me think this description is correct.

I've said if before I'm a newb, please don't hesitate to point out my misconceptions. I'm here to learn. More experienced opinions are wanted.

I understand it just as bunny explained, "your reflux column does the actual stacking of your distillate". That just means the most volatile vapors accumulate at the top and less volatile vapors accumulate lower. In other words, the job of the column is to create this volatility/density gradient . LM takes off from the falling reflux while VM takes off from the very top vapors.

In the cleaning instructions it says, "I personally like the idea of blasting the still and condenser with acidic steam". Yeah that won't happen with a VM unless you force it, because the reflux condenser will knock down an incredible amount of vapor and there just isn't enough positive pressure to force the majority to exit the vapor take-off. There are different ways of forcing a VM to blast steam out of the vapor take-off. You can just plug the vent hole above the reflux condenser and turn the water to the reflux condenser off. You could also remove the reflux condenser entirely and just cap the top of the tee (I prefer this method). Now steam is forced to blast through the vapor take-off and through the product condenser.

[elbono]

There are different ways of forcing a VM to blast steam out of the vapor take-off.

Yeah, but my question is why do you need to force it?

[Salt Must Flow]

There are different ways of forcing a VM to blast steam out of the vapor take-off.

Yeah, but my question is why do you need to force it?

This is a quote from the link you listed.

2 - Vinegar Cleaning Run
Next, chuck the vinegar solution into your boiler, attach the still head, and fire it up. I personally like the idea of blasting the still and condenser with acidic steam - the problem if you don't run steam through it is that some areas (like the top of a liebig condenser) may be untouched in normal, condenser-on operation. Of course, as we're only boiling a vinegar and water charge, there is no fire danger - but there is still vapour being generated, so this is a good time to double check that your still is always open at some point to the atmosphere. Of course, normal caution is needed with hot steam, don't scald yourself. If your column has packing, it isn't necessary to have it in at this stage.

Blasting vinegar steam/vapor through (including through the product condenser and vapor take-off) is part of the standard cleaning run procedure. People with VM stills have to "force" steam to blast through because it would otherwise condense as reflux.

[Salt Must Flow]

Now that I really think about it ... I don't see how you wouldn't have to do the exact same thing with a LM too.

[elbono]

Now that I really think about it ... I don't see how you wouldn't have to do the exact same thing with a LM too.

[elbono]

On a LM or CM there's only one path, the vapor has a "choice" on a VM.

[Salt Must Flow]

On a LM or CM there's only one path, the vapor has a "choice" on a VM.

LM and VM both have vented reflux condensers. That's what requires being plugged or capped in order to "force" steam/vapor through the take-off and through the product condenser or product cooler in the case of LM.

CM only has one path for vapor to exit so blasting steam/vapor through it is easy just like a pot still.

[elbono]

There's a vent but unless the RC is overwhelmed there's no vapor path out the top. Why is there a difference between LM and VM? On a CM the vent is through the PC a bit different but still a way for vapor to get out

I've seen lots of opinions that VMs compress tails better. My current understanding explains that but I want to know if I got it right.

[Salt Must Flow]

There's a vent but unless the RC is overwhelmed there's no vapor path out the top. Why is there a difference between LM and VM? On a CM the vent is through the PC a bit different but still a way for vapor to get out

I've seen lots of opinions that VMs compress tails better. My current understanding explains that but I want to know if I got it right.

I suspect you may still be confused about this. This all goes back to the link you listed and the quote I listed from that link. I highlighted the portion which is what we've been talking about.

Think about a basic pot still. Hot vapor only has ONE physical opening the exit. 100% of all hot vapor can be "blasted" out and through the product condenser.

With a VM and technically a LM (like a Boka with a vented reflux condenser for instance), a reflux condenser and a take-off port ... you tell me ... how on earth can you get 100% of the vapor to "blast" through the takeoff if the reflux condenser is refluxing and you don't plug the vent hole?

I get what you're saying about not overwhelming the reflux condenser. What those cleaning instructions are talking about is "blasting" vapor through the take-off and product condenser.

[elbono]

No confusion at all. I know what my still does, I watched it. The difficulty getting vapor out the takeoff is what got me thinking about it.

If you run high power with water on a equal takeoff size tee VM with the takeoff open why doesn't 1/2 the vapor "blast" out?, with alcohol it does. Only a very small amount exits the takeoff with water.

I have no doubt what happens, my question is why does it happen?

[elbono]

I agree with your original post in this thread, I'm questioning why it is that way.

[shadylane]

I keep finding statements like, "LM has very good heads compression (probably the best of the three main design types)". People keep saying, "LM is great for heads compression", " LM is exceptional at compressing heads", but I haven't found a single explanation as to how/why.

LM, VM or CM are all the same for compressing heads.

[elbono]

LM, VM or CM are all the same for compressing heads.

Do you think there's any difference on tails?

[Salt Must Flow]

Like bunny said, the column is what does the stacking/fractionation. The design of the still head only determines the manor in which vapor at the top of the column is taken out of the still. Either as liquid or vapor. As soon as tails shows its ugly head, I just shut down.

[shadylane]

ALL three designs work equally well at separating heads.

A VM has the narrowest range.

A LM can be designed to be run in potstill mode, but the cup would need to be big to catch all the liquid. That would make it tend to smear with the same sized up being used to neutral.

Of all the still head variations a CM has the widest range of operation.

[shadylane]

LM, VM or CM are all the same for compressing heads.

Do you think there's any difference on tails?

If you wish a CM can pass more tails or should I say a less refined shine.
Works good for making whiskey, rum or other flavored spirts.

[still_stirrin]

I’ll add a few pennies worth of opinion as to why or how a liquid modulated reflux head compresses the heads better, at least as far as my experience has taught me.

Because a LM uses the condensate takeoff vs return to regulate the reflux ratio, the top end of your boil will be filled with the most volatile constituents. And that is condensed with some of the liquid taken off while the rest is spilled back down the column into the packing, where it interacts with more hot rising vapors. The thermal exchange in the packing will cause a reflash of the condensate and more volatiles will rise again as vapors while the less volatiles will continue to fall until it is reheated enough to again boil. Since these falling constituents are less volatile, the temperature at which they reboil will be higher. So the top end of the column will be “stacked” with higher volatility towards the top and lower volatility constituents lower in the column.

The LM regulation allows a slower separation between the reflux portion (liquid that spills over the plate or out of the collection cup) and the portion that progresses towards the product condenser (and your collection jars). This liquid split has a higher reflux ratio (ratio of the liquid volume returned down the column to the volume taken off the still). As a result of this higher RR, more of the boiler charges higher volatile constituents are “compressed” towards the top of the column and condensed in the LM cup or plates for takeoff.

How does this compare to the vapor managed reflux column? I’ll speak to the conventional VM stillhead exclusively here. Since the reflux ratio is managed by the vapor split between the reflux condenser and the takeoff (a conventional valve), it is not affected by fluctuations in vapor production rates or the reflux condenser’s coolant flow rates. The RR is completely controlled by the vapor split (the physical ratio of vapor that goes up to the reflux condenser and consequently sent back down the column for reflux to the vapor that progresses to the product condenser through the VM valve).

Now, with a VM head, you can manually adjust the valve so the takeoff is very slow which would produce a higher RR and consequently collect higher volatile constituents towards the beginning of the collection. In this regard, it would “compress” the front end of the run similar to the way the LM does. However, since the return:takeoff is in a liquid state (in a LM head), it is more effective at capturing the higher volatile constituents because they’ll boil (and condense) at a lower temperature. In the VM head, the return:takeoff is in a vapor state and the higher volatiles haven’t been separated to the same degree. I could relate this to the energy potential of the vapor and liquid states of the produced vapor, but that gets deep into the physics of how distillation works.

One advantage of the VM design is that it is a “set & forget” control, because as I noted already, the reflux ratio is determined by the valve alone and is independent of the vapor production rate (remember, this is dependent on the heat input to the boiler) as well as the coolant flowrate. This makes the VM very stable operating throughout the run.

Operators of VM stillheads will note that the product’s purity stays high through the run even as the production rate at the spout (takeoff from the product condenser) will slow almost to a stop at the end, ie - drip, drip, drip, or slower. Yet, the measured %ABV will still be as high as it was throughout the run.

I don’t believe that the VM actually “compresses” the tails, rather it allows collection of the late hearts and leaves the less volatile “sludge” in the boiler. With the LM, as you approach the backend, you’ll notice the %ABV sink like a rock. And remember that with the LM head your takeoff rate is determined by the needle valve setting so the liquid takeoff will be constant even though the %ABV plummets.

The bottomline here is how the reflux ratio is managed or controlled during the run. The LM head uses the liquid takeoff to control RR while the VM head uses the vapor split to control the RR. And it is the RR that separates higher volatile products from lower volatile products.
ss

[shadylane]

I've said "LM, VM or CM are all the same for compressing heads."

But CM has a theoretical advantage over the other still heads.
The top of the column is filled with the most volatile constituents.
A dephleg then controls what sneaks past based on how volatile it is.

[Saltbush Bill]

theoretical advantage

Theoretical advantage is what it is in my opinion, Id be very, very surprised if the average distiller could tell you which product was drawn off from VM , LM or CM still in a blind taste/ smell test.

[zed255]

Any reflux still can produce any result, just depends on the operators understanding of the differences and how the still is run.

An LM might be easier to get well compressed fores / heads than a CM or VM for the average distiller, but a skilled operator could get similar results without regard to the still type.

I like the VM (actually a CCVM in my case) for its 'automatic' kind of operation once into hearts and am willing to play with it to get better compression at the start, i.e. running slower then speeding up via coil adjustments. When I ran an LM configuration getting well compressed fores / heads was easy, but required nannying through the run to keep hearts quality high and consistent and being ever vigilant of tails. I have not run a CM, though I could envision it working well at compressing the front end of a run well, just requiring operator attention.

I'd really like to try an combination head, LM / VM seems sensible, to try and gain the best qualities of each.

[shadylane]

A LM still head has one very real advantage.
It doesn't need a product condenser.

[Bushman]

I agree with the previous comments but I will add to the comment, “depending on the expertise of the operator’ to include the build of the still. If you read any of the prior posts of 2010 and earlier a lot of them have negative comments about the CM still. The reason was the design of the still that gave very little reflux and was more like a pot still with a few through pipes for cooling. This design did not give the operator an opportunity to reach 100% reflux or control reflux at all.

[zed255]

A LM still head has one very real advantage.
It doesn't need a product condenser.

True, to a point. I still ran a small liebig as a product cooler, otherwise the output was very hot. You don't want to over-cool your reflux condensate to avoid upsetting the column. With this in mind, the product only gets enough cooling to condense and not much more in an optimized set-up.

[Saltbush Bill]

. If you read any of the prior posts of 2010 and earlier a lot of them have negative comments about the CM still. The reason was the design of the still that gave very little reflux and was more like a pot still with a few through pipes for cooling. This design did not give the operator an opportunity to reach 100% reflux or control reflux at all.

Very true Bushy, and people are still buying and selling those and worse.

[Dancing4dan]

I feel like I have to be missing something or maybe I'm misunderstanding. I keep searching and reading everything I can find. I keep finding statements like, "LM has very good heads compression (probably the best of the three main design types)". People keep saying, "LM is great for heads compression", " LM is exceptional at compressing heads", but I haven't found a single explanation as to how/why.

I understand that LM collects what condensates directly from the reflux condenser. I understand that the take-off rate is variable. I understand that any excess reflux overflows the collector and falls onto the packing. So exactly what about this makes it better at compressing heads?

Just for clarity, I know what compression is. For instance with my still, tails is held back very very well. Suddenly I'll see the vapor temp rise and tails comes right away. So if we are to define our terms, that's an example what I believe "compression" is. I just can't fathom how LM "compresses heads". It just doesn't make any sense to me at all.

The only explanation I can think of is that people are taking off 100% of the reflux which is specifically something other still designs cannot do. Other still designs can do a similar thing by allowing 100% of the rising vapor to leave the still (after stabilizing), condense it and collect it. So in this case there's really no difference. What am I missing? Is this just a myth, old outdated info?

Don’t know how or why. It is my experience though. With my LM/VM combo reflux still heads are more concentrated and make up a smaller volume than if I use VM mode to collect the heads. I think it has to do with this specific design and LM collection set up and a slow take off rate through heads.

The VM compresses tails and you can see it happen if there is a sight glass above the reflux material. I use copper. As soon as there is a visible fog on the glass, stop product take off and reflux for a few minutes. This seems to wash the packing of and precipitated tails. Then I restart product take off slowly until the glass fog starts again. Starts again pretty quickly. Then it’s all over.

[drmiller100]

I've never ran a vm still.

Still_stirrin and others used their descriptions and I agree a Lm can be very concentrated heads.

I believe the way to concentrate the heads is to run it in full reflux a while. Then pull everything off the top on one dump. Should be a table spoon or two.
repeat.
Repeat a third time. If it is still nasty you can go again.

Or. You can pull heads one drop at a time so the nasties get diluted with good etoh.

If you take a virgin wash in a good column at full reflux the nasties will be at the very top of the column. Flush them all at once. Then restabilize the column.

If you want a consistent LM column regulate the reflux and take the overflow as product. This is effectively what my understanding a vm does but with a lot less work to build.

Caveat I can't make it taste or smell good.