UPDATE: Results from the technique in this thread of changing the limiter rod configuration were dubious at best. Actual measurable results were attained by modifying the width of the limiter rod, discussed here: Modifying thermosiphon flow rate on vintage Faema Levers

With my 2 group Faema President the left group has always run a bit hotter than the right group, which I didn't mind because it allowed me the choice of which group to use depending on the roast level of whatever beans I was using. But of course my need to tinker got the best of me, especially because my cooler group could still get just a little to hot for my liking on the darker roasts, so I decided to futz with the thermosiphon limiters on my Zodiaco groups to see what sort of configuration range I have.

Not much seems to be written about these things (other than some comments I've seen about doubts of whether or not they actually do anything, I assure you they do) so I figured I would document my personal experience for the benefit of other Zodiaco group owners.

The first thing I did was completely remove the limiter rods from both groups, while the machine was off of course.
My first mistake was not to document their configuration before removing them, so I suggest you do that somehow so at the very least you can return your group to its original configuration.

At any rate, here is an example of one of the rods:


The semicircle part of it allows water in the thermosiphon to pass through the group, heating it to the appropriate temperature to make coffee. By turning the rod you can restrict the flow of water through the thermosiphon, restricting the amount of heat that can be passed to the group. The less water that passes through the group, the cooler it stays. Theoretically, a quarter turn would be all that is needed from fully open to fully closed.

To test this out, I marked the "missing half" of each limiter rod (metering rod?) with a Sharpie and screwed them back in to completely close off the left group (the one that used to run hotter) and completely open the right group (the one that used to be cooler).


The results were as expected. The right group heated up nice and hot while the left group stayed pretty much room temperature, even after a few hours. It never got hot enough to even be able to make coffee.

Experiment success, I proved I can manipulate the group temperatures just by fiddling with those rods.

Now came the problems. I had forgotten to log my original configuration, leaving me sort of flying blind as to whether my adjustments are helping or not. I have found that it takes at least half an hour for any adjustments you make to show an effect, and having a quarter turn as the entire range means that even small adjustments can have big effects.

After an entire weekend of further futzing with the rods, I eventually got to a real happy place here

with the right group hot and the left group cool, but hot enough to make non-sour coffee for darker roasts.

You will notice that I flipped the configuration of the right group 180 between the two pictures. This is still a mystery to me, but it certainly seemed like the group gets hotter with the limiting rod open to the right than it does open to the left. I don't know how this could be unless the therrmosiphon entrance is horizontally off-center somehow.

Thanks,

Anyone else have any good experience to share on this group?

Great job, Dominick!

I'd like to reduce the group idle temperature a few degrees, so I am going to play with it over the weekend.

Now, did you see that you can also adjust the amount of water that hits the puck during preinfusion? That's the screw underneath the group (part #104261).

Thanks Dominick. I am thinking about the same question.

vberch wrote: Now, did you see that you can also adjust the amount of water that hits the puck during preinfusion? That's the screw underneath the group (part #104261).

The part #104261 is just a cap. The screw is #104260.

vberch wrote: I'd like to reduce the group idle temperature a few degrees, so I am going to play with it over the weekend.

Cool! Just make sure you mark its original configuration somehow before you start as a reference, had I done that at first it would have saved me a ton of headache this weekend!

vberch wrote: Now, did you see that you can also adjust the amount of water that hits the puck during preinfusion? That's the screw underneath the group (part #104261).

I did open that up on one of the groups to increase the preinfusion flow, and I ruined a screwdriver getting it to turn initially, but I haven't tried to do any fine tuning yet. My left one is open all the way and I think it might be thrashing the top of the puck a bit, so I'll have to adjust it at some point. I just don't really know how to "mark my settings" on that thing in any reliable way.

pizzaman383 wrote: Have you found that limiter setting also impacts the shot temperature, too? Is the restrictor located before our after the two paths of the thermosiphon converge?

Yes, my cooler group makes a cooler shot, all other things being equal.

I think the limiter just covers the entry path, at least it looks like that in vberch's diagram, but I would have to actually take a group off to verify.

Dominick, there is no point for me to remove the limiter rod completely. I am just going to turn it 1/8 of turn, see how it affects temperature, turn it 1/8 of a turn, see if anything changes, etc. I am going to measure idle group temperature before and after and give it 1hr to stabilize. We'll see.

dominico wrote:I did open that up on one of the groups to increase the preinfusion flow, and I ruined a screwdriver getting it to turn initially, but I haven't tried to do any fine tuning yet. My left one is open all the way and I think it might be thrashing the top of the puck a bit, so I'll have to adjust it at some point. I just don't really know how to "mark my settings" on that thing in any reliable way.

Just a note for anyone playing with the thermosiphon limiter, if you wind up closing it off completely at any point you may create an air bubble, effectively making the thermosiphon not siphon anymore.

You will know this has happened to you if you know that you have readjusted your limiter rod to a configuration that allows flow and yet your group still isn't getting any hotter after an hour.

If this happnes you need to purge the air bubble to "kick start" the thermosiphon again. A simple way to do so is simply to pull down the lever and run about 6oz of water through the group.

Very interesting Thread!