If this is true, I shouldn't change the position of the restrictor. Because when pulling a shot, in the upper tube it will slow down the hottest water from the HX, whereas in the lower tube it would slow down the cooler water from the HX. Am I right?
Never thought there would be so much to this! But I gained a lot of insight from you guys. Thanks!

I believe that the "search function" on various coffee sites is a good friend. For EXAMPLE:
http://groups.google.com/group/alt.coffee/search?group=alt.coffee&q=thermosyphon&qt_g=1&searchnow=Search+this+group

The thermosyphon system, which is a major part of many espresso machines is, very simply, complex. There is an abundance of variables to take into consideration, not the least of which would be the duty cycle one plans to impose on the machine, the condtion of the machine that duty cycle is to be imposed upon, and the specific machine itself. If it were as SEEMINGLY simple as say, a solar hot water heater (essentially same principles), maybe we could all be happy.

Out of curiosity, what size restrictor did your distributor send you and is there a smaller size available? Maybe knock your pstat setting down 0.10 to 0.15 bar, assuming you won't have any steaming complaints before and/or after.

another_jim wrote:This is the big difference between domestic E61 boxes and the real ones: the real ones are tuned to produce a group at the desired temperature. The fixed restrictors on the Domobar may help, but they don't do this. It makes more sense (to me) for the variable restrictor to be on the return side, so I may be misremembering.

Jim, some iterations of the genuine FAEMA E61 have the variable restrictor. This is not to say that that is the only way to get the desired temperature at the group without too much overshoot.

I know that many commercial machines use a fixed diameter restrictor. In dealing with the manufacturer of the machines being manufactured to the specs of my former work place, the manufacturer had a whole set of different fixed restrictors correlated to a number of brew temperatures. The NS Aurelia is probably a commercial machine that people will be familiar with that uses fixed restrictors. Conversely, a friend of mine recently bought a 1964 FAEMA E61 that did not have the variable restrictor and he fixed it by putting in fixed diameter restrictors (that machine now makes beautiful espresso effortlessly).

Whether or not fixed restrictors have been applied with the requisite care in domestic E61 boxes is another question. I know that something like four years ago, David Makin had the manufacturers of his E61 box put in an appropriate set of restrictors. I know this, because I have been enjoying a domestic E61 HX box that pretty much does not require a cooling flush (as measured with a thermofilter and, more importantly, with my tastebuds) since 2006. As far as I know, Expobar was the first brand to provide restrictors for their machines in Australia, though they still ran a touch hot for my liking. Most E61 box manufacturers in Australia seem to have jumped on the bandwagon ... or so they claim.

I guess that the question for people with unrestricted E61 boxes in the North American and Canadian market is how they can go about getting their machine to perform as they want it to. Frankly, if the domestic E61s around are as horrible as everyone says, I think that you should all be pinning it on the importers and vendors. They can determine and procure the appropriate restrictor set much more easily than we can. It might even be a simple matter of putting a phone call in to the manufacturer and then waiting a few months for a $2 part. I have to say that I find it pretty mindboggling that anyone would be selling burn boxes in this day and age.

There's one final aspect that deserves to be addressed, an that's the idea of adjusting brew temperature. Frankly, I don't know that restricted E61 boxes are really very well suited to this. I played around with mine with a thermofilter very briefly and I think that increasing the pstat setting 0.1 bar makes a difference of around 2C at the head, which could be useful ... in fact, I have a hole drilled in the top of the machine to allow access to the pstat for just this purpose. Flushing on my machine, from recollection, doesn't actually make all that much difference. Swapping out restrictors is impractical. In this respect, a variable thermosyphon restrictor looks like it could be good fun. However, the simple truth is that 99.9% of purchasers of even these very high end domestic machines won't actually benefit much from the ability to change brew temperature. Frankly, I think that most professional baristi don't actually benefit from it. Despite changing brew temperature frequently when working on a Synesso Cyncra for a few years and then a FB80 for a few more, I seldom feel the need to play around with the brew temperature on my E61 box; changing the grind and dose offer the most dramatic changes in flavour.

Cheers,

Luca

It is almost philosophy: the more we know, the more we know that we know nothing. But it is starting to make sense to me nevertheless .
There is one thing that bothers me: I can see that because of the slower flow, the temperature of the water in the syphon has gone up (it stays longer in the boiler), but because there is less flow, the temperature of the grouphead as a whole has gone down (less heat energy is transferred) . Indeed the intitial watertemp is higher, and the big screw that attaches to the mushroom is hot now (water sizzles when it touches on the outside now). So some parts of the grouphead seem to be hotter and some must be cooler than before. As Ed already said, one thing counterbalances the effect of the other. But how to know the net effect? Is it like a coin on its side: we just don't know which side it will fall to?

Oh, by the way, Eric, I didn't measure the hole in the restrictor, but I could swear it was less than 2mm.

another_jim wrote:Has anyone ever tried my pet idea, a solenoid valve in the return driven by a thermostat or PID controller using one of Eric's grouphead sensor?

Well, almost.
I started with just a variable restrictor in the siphon return, using this to throttle down the group to the target temperature, based on EricS's T/C adapter.

But a breeze, or maybe even a sneeze, and sometimes a shot, would stall the siphon. So I added a solenoid valve as a restrictor bypass, using the alarm (too cold) function on a PID. So I'm not really controlling the temp with the solenoid. But I suspect you could set the restrictor to run slightly hot (and so slightly faster, and so less likely to stall), put the solenoid valve in series, and use a conventional PID in cooling mode, starting and stopping the siphon for temp control... as long as it started up reliably every time.
-Ed

Spironski wrote:It is almost philosophy: the more we know, the more we know that we know nothing. But it is starting to make sense to me nevertheless .
There is one thing that bothers me: I can see that because of the slower flow, the temperature of the water in the syphon has gone up (it stays longer in the boiler), but because there is less flow, the temperature of the grouphead as a whole has gone down (less heat energy is transferred) . Indeed the intitial watertemp is higher, and the big screw that attaches to the mushroom is hot now (water sizzles when it touches on the outside now). So some parts of the grouphead seem to be hotter and some must be cooler than before. As Ed already said, one thing counterbalances the effect of the other. But how to know the net effect? Is it like a coin on its side: we just don't know which side it will fall to?

Oh, by the way, Eric, I didn't measure the hole in the restrictor, but I could swear it was less than 2mm.

I am not sure anymore, was all this bullocks? I would think that the grouphead will go to a state of equilibrium. So how can it be that one part of the group actually got hotter while the group as a whole became cooler? Come to think of it, this seems nonsense.
My cooling flush could have become shorter because the pstat seems to be influenced by my modding the machine. Now it cycles around 0,8-1,0!

It looks like the flowrestrictor had no effect whatsoever! Anyone an idea how I could shorten my cooling flush? Now I wonder what would happen if I drilled the hole in the restrictor to, say, 2,5 mm...

What's really unfortunate is that Home-Barista.Com doesn't fund field trips to investigate problems

The pstat simply responds to pressure changes in the boiler (I'm guessing you kinda know that one) and the addition of a thermosyphon restrictor would NOT change the absolute values that the pstat is on/off. It should, however change the frequency of that on/off and that would be to reduce the cycling. The water flow in the thermosyphon system causes some of the steam in the boiler to condense, reducing the pressure and providing an "on" signal to the pstat. The pstat would still cycle (at a greatly reduced rate) with zilch flow in the thermosyphon due to boiler heat loss to ambient.

A restrictor will reduce idle grouphead temperatures and thus reduce cooling flush requirements - did you not report these results a few posts back? It will also inherently increase the recovery time between shots - all other factors being equal.

Before you modify your existing restrictor, I would order one or more from the distributor and inquire as to their size.

Thanks Eric,

This would be an expensive field trip!
It could be that I knocked the pstat during my fumbling with the machine, and that this caused the pstat to change. It is only 0,1 lower now, but that would still influence the temp.

I would have thought that adding a flowrestrictor lowered the temperature of the grouphead, that is the common believe, right? But now I have come to the believe that it was only the lower pstat that was the source of the lower volume of the cooling flush, and that the temperature of the grouphead hasn't gone down at all. For now some parts of it seem actually hotter than before! I have never witnessed sizzling water on my grouphead before. And being bronze I cannot imagine some parts became hotter, and at the same time other parts became cooler. The extra heat would simply dissipate (is this the right word?) into the cooler parts, would it?

So now I am thinking what to do. The restrictor already cost me €15, so I don't want to order a bunch of them. And as far as I know, there is no telling what a bigger hole in the restrictor would have for an effect, right? Would it change anything if I put it in the lower pipe? According to Bluecold water also comes through the lower pipe when pulling a shot, so that would worsen the effect because higher up the HX the water will be hotter....

I will contact the importer about this. Thanks for thinking with me...

On recommendation from Eric, I installed the manufacturer specified thermal siphon flow restrictor in the lower port of the GH on my Lyra in an attempt to reduce the volume of the cooling flush. The Lyra parts diagram shows the flow restrictor should be placed in the lower port. I don't know why it was missing although I got my Lyra used. I use Erics thermocouple adapter to monitor "GH temp' and noted a reduction of the idle GH temp of several degrees and reduced volume for the cooling flush after installing the restrictor. The diameter of the orifice in the stock flow restrictor is 3mm. The flow restrictor orifice of 3mm is significantly greater than the 0.5mm orifice of the gicluer so I had rationalized that the flow restrictor has little to no effect during the extraction. Comments anyone?
When I have some time on my hands with nothing to do, I'm thinking of machining another restrictor with a smaller orifice of 2.12mm diameter to possibly better tune the idle GH temperature and of course reduce the cooling flush more...