...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

And here is a more detailed reply:

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?

Certainly you would reduce the cooling flush requirements-- I agree with that. As regards recovery time, a better statement on my part would have been that you increase the recovery time relative to the particular machine in question. As the OP has a Quick Mill Anita (as do I), my response was inherently slanted towards that line of machines (Anita, Andreja, Vetrano). Whether or not it is a correct answer for an Elektra T1 is, perhaps, up for grabs, with a tilt towards me being incorrect-- and here's my take on why. Saying this with a slight smile "I don't believe a machine that has a 6 liter boiler and 2000 watt heating element has any problems whatsoever with "recovery" that would be better applied to the human side of the PF as said human is trying to keep up with the Elektra's capabilities before keeling over in a pool of sweat.

The same cannot be said for the Quick Mill machines at their normal(?) pstat settings of 1.10 to 1.25 bar (maximum gage readings) and, if they were set to duplicate your setting of 0.80 to 1.00 bar (min to max), ya better grab a pillow.

When I said "there is no such thing as a free lunch", I meant that you would need to sacrifice some in the ability of the machine to pull rapid consecutive shots. If you have a machine that can do this rather easily with no modifications (Elektra), you sacrifice nothing(?). On the other hand, if the machine is either hard pressed to accomplish this or simply cannot, I believe a thermosyphon flow reduction will penalize that particular aspect of the machine's performance (recovery).

Shouldn't the Hx water heat back up to boiler temp at the same rate as before the mod?

I don't think so because you are inherently inputting less energy into the boiler as would be evidenced by a reduced total "on-time" for the heating element. The amount of energy you need to put into the boiler (steady-state idle) is governed by the heat loss to the environment by the grouphead, the thermosyphon lines, and the boiler itself. The major change the mod makes is in the temperature of the grouphead -- as it was supposed to do. While it surely varies from machine to machine, idle condition hx outlet temperature is about 15-20 degrees less than AVERAGE boiler temperature.

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?

At the end of a shot, Anita's grouphead temperature goes below desired brew temp because, at least momentarily, a reverse thermosyphon action takes place. A lot of this will also depend on the technique used to pull the shot. The size of the hx in Anita is small -- 110 ml.

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 kinda believe the Elektra is designed for a more rigorous duty cycle than Anita or her siblings. It would be interesting, of course, to compare Elektra's flushing temperature "curve" to Anita after agreeing to a specific baseline and flushing volume. But that would just be for fun -- I don't think anything could be gleened from the comparison. I also believe Elektra's grouphead has a little more mass than the standard E61 which would buoy your statement as regards temperature changing very little.

I don't believe you "need" the recovery to 211 but if you really wanted to compare apples to apples, you should judge the recovery time back to the original starting point, whether it be 211 or 204. If the Elektra (or any machine for that matter) can demonstrate EQUIVALENT performance under a strenuous duty cycle but at a lower grouphead temperature, then I would reach the conclusion that the Elektra's engineers should have kept the lights on a little longer. Or perhaps there is something that I am missing . . .

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.

Well, I would have to say you are correct for a particular class of machine, e.g. the Vibiemme Domobar has a 2.0 mm restrictor (dealer applied) to the hx outlet and I have seen zero complaints from owners re pulling multiple shots. If you do a search on A.C. for posts by Greg Scace (keyword = thermosyphon), you will also see where he increased the length of his hx outlet line (by a factor of 3) and succeeded in reducing the group temperature of his Astra from the low 200s to 198.

I had a little time this evening to play with the thermosyphon mod. It was interesting. I'm convinced that a restriction in the upper line is detrimental - at least on my machine. With this variable restrictor (Cv factor .5 w/.187" orifice) installed and set at about 80% full open...:



...I saw these changes with the Gh now idling at 205F:

The Flush takes 10oz compared to about 6oz prior (edit; Not true - Corrected in a later post)
The group head temp peaks about 8-10 degrees cooler than prior during a flush
The group head idle temp doesn't seem to stabilize as well as prior

So, It seems that the restriction might behave better in the lower port, if at all (again, at least on this machine). I haven't had a chance to log anything yet, but will likely build a line with restrictor to replace the bottom line and then do all three configurations at once (well, maybe in one weekend).

Has anyone seen this reaction from adding a restriction in the upper line before? After thinking about it, it seems like that since you're now drawing more water off the bottom of the Hx than the top, that this would be expected. As a complete novice though, I have to believe that someone has played with these configurations before.

Cheers,

Brad

I have to believe that someone has played with these configurations before.

Do the search on A.C. as I suggested and you will gleen a lot of info. What parameter(s) are you using to judge the completion of your cooling flush?

erics wrote:Do the search on A.C. as I suggested and you will gleen a lot of info.

Wilco!

What parameter(s) are you using to judge the completion of your cooling flush?

Strictly temperature. Heck I couldn't imagine hitting two parameters at once! Here is a chart from a few days back - it's all I have handy, but it will show a typical flush.


Cheers,

Brad

Well, I haven't had time to do everything that I wanted to do yet, but will make an update on "learning out loud"

With the upper thermosyphon restriction, the flush didn't take more time or volume as I reported initially, what I was seeing was that the temperature indicated in the GH took 10 oz to reach the point where I flushed to before (192 degrees for a delayed shot [which I also learned is too low anyway which is why I was always on the ragged edge of sour shots]). I had to cobble together a thermofilter to verify this:


This works ok, with the exception that it has too much dead volume and no filter to keep grounds out of the needle valve. A buddy is working on a teflon insert and sintered filter for it, along with moving the probe above the insert, which should help significantly.

So, the thermofilter indicated that I was extracting a bit cool, likely in the 190 - 193 range , while my GH TC was indicating 201-203. But the interesting part was that the machine seemed "unstable" for lack of a better description. You could stop the flush immediately at the end of the flash boil, and the brew temp immediately after in a sim shot would be anywhere from 188 - 205, using the correct metered flow. When pulling an actual shot, the taste pretty much mimicked the wild temp variations. Why the GH temp seemed to indicate so wildly, I have no idea.

This variable restrictor that I used is offset which may effectively decrease the cV even more in low flow conditions, I don't know. A fixed restrictor may perform better. I would post a chart of this behavior, but honestly, they look like a madman was at the wheel. ...and maybe there was, I'm no longer sure!

Now, consider Elektra's design: The Hx upper and lower fittings are identical, as are the GH upper and lower fittings. However, the lower (return) line is 10mm tubing, while the upper (supply) line is 12mm tubing with the nipples machined down enough so that the nipple will fit a 10mm tube fitting (and a 10mm nut which has the port slightly enlarged to, again, fit over the 12mm nipple. (These may be OTS items, but definitely obscure to me) Why would they do this when it would be easier to just use two 10mm tubes?:

A. Because the 12mm supply tube would flow more water during the brew cycle allowing proportionately more hot water to exit the top of the Hx than cool water exiting the lower tube? (The smallest cross section in the loop is indeed the 10mm tube/nipple inner diameter (ie 8mm ID), as it is smaller than the bore of the fittings)

B. Because the 12mm supply tube would allow more cooling when static (in thermosyphon mode) between the Hx and GH by allowing the water to dwell slightly longer before entering the GH?

C. A combination of the above.

D. None of the above.

I think "C". In any case, folly or no, I put the machine back to stock configuration with this thought in mind - maybe the proper way to maintain a lower group head temperature is as Greg Scace posted in AC and EricS so patiently pointed me to - increase the radiant heat loss (temperature drop) in the thermosyphon between the Hx outlet and GH. Could this be what Elektra accomplishes to some degree with the 'imbalanced' supply and return lines? Dunno, but there it is. Frankly, what's a couple of ounces of water each flush, really The only other logical alternative that I see is to restrict both ports maintaining the same 10:8 ratio, and that's if you believe that "A" above alone is the design goal.


On the bright side, while I was poking around inside the T1, I finally had the ambition to fix a problem with a nervous pump pressure gauge. The supply line to the gauge would always be filling with water and becoming erratic. You could remove it, blow the water out and reinstall it, and it would work ok for a couple of sessions, then slowly start getting worse until it was recklessly shimmying +/- 1b during a shot. Not the end of the world, but definitely annoying. So, I mustered up the courage to do this:



Just simply a 4mm tubing coil placed in-line in the original 6mm tube. I would have replaced the entire tube to reinstall if she's ever sold, but don't have access to those fittings. It works well - not overly damped, and steady as a rock.

As far as thermosyphon temp limiting, I think I'm happy back at stock. Maybe If I had an old used commercial machine to play with in the basement...

Cheers,

Brad