...Good question! Topic split from Buyer's Guide to the Vibiemme Domobar Super by moderator...




Thanks for the excellent and detailed write up, Dave.

Reading about the gicleur in the VBM made me wonder if it would be worthwhile to install a similar restrictor in other types of E-61 machines to reduce the group idle temp, and diminish the need for cooling flushes. For example, my Anita idles at about 210 degrees after an hour or so, and requires a fairly long flush of six ounces or so to get it down to proper brew temp. If I were to install a restrictor in the thermosyphon, it seems like I could reduce the amount of flushing needed.

Would the VBM restrictor fit into another E-61 machine? Is it a bad idea to try it? Seems like it would be a fairly cheap and easy way to improve the machine's practical performance.

Eric and I e-mailed about this the other day.

I think it is a great idea, or take it one step further and use an adjustable valve, similar to the commercial Faema restricor.

As seen in Abe's Expobar Brewtus Review:


Faema E61 Legend thermosyphon flow restrictor (photo courtesy of Ninth Street Espresso)

I've seen pictures of that adjustable flow restrictor before, but it seems like it might be a much bigger project to find one and add it to the machine. Getting a small plastic gicleur and plugging it into the thermosyphon would seem to be a much quicker and cheaper solution, though obviously you lose the adjustability feature. Still, if you know of a relatively cheap and easy to obtain part that would do the job and wouldn't be too hard to add to the machine, that might be the best way to go.

My experience with the VBM has me thinking of putting a thermosiphon restrictor in my Elektra A3. Remember that the heat exchanger still contains super heated water and needs to be flushed prior to the shot, but the flow restrictor keeps the group at a nice manageable temperature and makes the flushing much easier.

Beezer wrote:Getting a small plastic gicleur and plugging it into the thermosyphon would seem to be a much quicker and cheaper solution, though obviously you lose the adjustability feature.

Jon shows the steps in Installing thermosyphon restrictor on expobar office pulser, but he had the advantage of a properly sized restrictor. Then again, if you had Eric's handy thermocouple adapter, a nylon disk, a bunch of drill bits, and a lot of patience, it sounds doable.


Mysterious white disk is secret to taming the "Expobar Dragon"

Interesting placement, he put that on the upper line in the group, the VBM"s restrictor is located in the upper thermosiphon line but at the boiler connection. I do not know if that makes any difference but I would think that the boiler side mounting would make removal easier. With it set back inside that group it looks to be a pain to get out if you needed to remove it.

The manufacturers and distributors of our machines are really in a quandary. What sort of service will the machine see? Will it be asked to pull three shots in three hours or three shots in three minutes? Is the machine going to (and staying in) Denver, Colorado or New Orleans, Louisiana? What is the relative "power" of the thermosyphon system in the machine as designed?

I believe it is worthwhile to install a thermosyphon restrictor of some sorts in a few E-61 hx machines (Izzo, ECM Giotto, & Expobar come quickly to mind) but not necessarily in Anita (or Andreja or Vetrano). I mention the Izzo because I have measured one and found it to run ~ 5 degrees above the Quick Mill machines for equivalent pstat settings. I mention Giotto because it and the Vibiemme Domobar are essentially identical internally. The adjustable thermosyphon restrictor installed in the Faema Legend certainly APPEARS to be a good solution-- a reasonable compromise between the added cost and complexity of automatic control and the simplicity of mandatory user intervention to fit various operating modes. The orifice size that Jon used in his Expobar is 2.5 mm, Expobar P/N 50020020; I believe the orifice sizes available for the Vibiemme are 2.0 & 3.0 mm, with the 2.0 being typically installed; the orifice sizes available for "standard" E61 groupheads are also 2.0 and 3.0 mm but they appear to be installed at the group end vice the Vibiemme installation at the hx outlet end. I can think of no reason (from a performance standpoint) as to why it would make any difference as to where they are installed. For a pictorial of these, go here:

http://www.nuovaricambi.it/index.html

Click on English, Coffee Machines, Faema, then Scheme 11.

For someone wanting to experiment with various sizes, the style of the Expobar thermosyphon restriction orifice is, by far, the easiest to replicate. The OD of the teflon disk is 0.718" and the thickness is 0.078". A way to do this would be to buy 3/4" teflon rod, turn it down to the dimension in a lathe and drill it (in the lathe) to whatever dimension you wanted and then slice the disks like bread. Total cost would be about $15, would take about 30 minutes, BUT of course, that requires a lathe. Applying a variable restriction (a la Faema Legend) to Anita would be tough because of space constraints - not impossible but . . .

Keep in mind that restricting the thermosyphon flow will inherently increase the recovery time for the machine but this may be JUST PERFECT for some users. Personally, I have (and I know it sounds crazy) become accustomed to the cooling flush and I would not judge this to be a worthwhile adventure for the Quick Mill machines. At the same time, that is not to say this adventure has been scratched off my list. There is plenty to learn about these machines and I am having a good time.

erics wrote: Keep in mind that restricting the thermosyphon flow will inherently increase the recovery time for the machine but this may be JUST PERFECT for some users. Personally, I have (and I know it sounds crazy) become accustomed to the cooling flush and I would not judge this to be a worthwhile adventure for the Quick Mill machines. At the same time, that is not to say this adventure has been scratched off my list. There is plenty to learn about these machines and I am having a good time.

I'm really curious about this. On my T1, the group idles at 211 degrees when completely stabilized (running the boiler at .8 - 1.0 b and measuring at the "port"). If I reduced the thermosyphon flow to the point that it idled at, say 204, I would reduce the cooling flush noticeably because the brew water would not leach as much energy from the group mass, correct? How would this lower group temp effectively increase recovery time?

Shouldn't the Hx water heat back up to boiler temp at the same rate as before the mod? At the end of the shot, wouldn't the group head be relatively close to brew temp, or likely somewhere between high idle and brew temp? From what temp profiling I've done, it appears that the group mass itself actually changes relatively little during brew activity, whether it be cooling flush or pulling a shot. Granted this was measured on the outside surface of the group head, not in a well, for instance. But I don't understand why you would need the "recovery" to (in my case) 211, if that's what's implied by your statement.

I just don't see how there would be any detriment to keeping the group internal temp closer to the target brew range, as long as you didn't reduce the group idle temp to the point that it's below the target brew temp, and any temp above that would really be wasted thermal energy.

Or, does some excess temp recover the pf temp more quickly? Help me understand this!

Cheers,

Brad

Greetings Brad -

By recovery time, I mean the amount of time that would elapse until the machine can successfully DUPLICATE the previous shot. Does this mean that you have to get back to 211? Well, ideally, yes. In reality, the climb back to 211 is asymptotic and if you initiated a flush at, say, 209, you would be flushing less for the second shot. I have never operated a T1 but I would think it could substantially (and understandably) outperform the Quick Mill machines.

The easiest answer to the thrust of your comments would be - there is no such thing as a free lunch. The size of the hx in the Quick Mill machines is, I BELIEVE, 110 ml. After pulling a shot, the AVERAGE temperature of the water in the hx is substantially below group temperature and I notice a reverse thermosyphon action taking place for a short while until the water then in the hx climbs above group temperature.

If one could adjust the thermosyphon flow such that the group idled at a specific temperature, say 198 F (as measured via a thermocouple adaptor or digital thermometer) and the AVERAGE temperature of the water in the hx somewhat higher, say 210 F, it would simply be a matter of pulling the shot with NO COOLING FLUSH whatsoever. If there were no downside to this, machine dealers would be working OT and then some to fill the orders.

The same scenerio applies to simply reducing the pstat to relatively low levels - say 0.70 Bar (max reading) and thus producing a grouphead temp of around 198 F (with the Quick Mill machines at sea level). You can then pull a shot with NO COOLING FLUSH whatsoever but steaming would be marginal and the machine would be limited to around one double shot every 15 minutes (as best I can recall).

The only time the brew water TAKES energy FROM the group mass is when that group mass is at a higher median temperature than that of the incoming brew water. This would be the case when using the flush-n-go technique of shot-pulling.

This may not respond fully to your comments - still thinking about that.

I do follow what you're saying, but no, I don't think it specifically addressed my question. However, I'm on the road today, and would like to pause this and reply early next week. I may graph it, if I can get the time, and that may answer my question. I have a metering valve that has been sitting around awaiting the ambition to do a thermosyphon mod, and maybe I will just try it and graph before and after. I had to order the fittings and tubing as I would like to just remove the stock line for later replacement.

I do want to convey the question properly at least, and not sure I have done that - maybe this will make sense, or maybe I am missing something elementary:

In a nutshell - the temperature of the grouphead in excess of brew temperature is wasted, and leads to longer than necessary flushing (as temp is added to the brew water from this excess heat in the mass). This energy comes from the boiler via the heat exchanger and the thermosyphon. In re: the free lunch - your're paying to cool this excess heat with a longer flush. So, if the group head idles at, or much nearer, the target brew temp, there should be no downside. You're saving water *and* energy. Further, shouldn't the recovery (to the new lower stable grouphead temp) be relatively shorter when compared to idling at the original *overheated* state?

Not sure if that is more clear, but hopefully. Thanks for your reply -

Cheers,

Brad