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