DanoM wrote:That is much easier to implement. Just a washer one size too small and filing/drilling out the hole to fit the dipper tube exactly, perhaps a non-conductive plastic washer on the group side to limit heat transfer with a small hole in it for ease of lever movement. Almost as temp stable as the saturated group too.

I'm not quite visualizing the non-conductive plastic washer on the group side. When I had a 2nd gen machine I cut a heat break gasket out of PTFE that fit between the group and boiler and added longer screws to make sure they still had a good grip.

Regarding water saturation, I believe that happens when you raise the piston past the upper gasket so water enters above the lower gasket, doesn't it? In that case whatever method you use to close off the steam port would be equal to another. A truly water saturated group would be something you would find in a commercial lever with a thermosyphon, or am I missing something?

If you draw out what DanoM has constructed and described you will find that the area above the piston is being filled by liquid forced into that above piston are through the dip tube and vented on the top region by leakage past this group neck plug. As the group is below saturation temperature then any steam is condensing to liquid and lowering the pressure in the group above piston area. This will soon reach a thermal equilibrium. Any liquid in the above piston area will ultimately be forced past the group neck plug on the lever up stroke. This is why what Robert described is a superior fix to accomplish this stability as there should be an unrestricted above piston return path to below the lowest normal water level in the boiler. Once thermal equilibrium is established any heating will require lever pumping to pull heated boiler water into the group.

If you get this thing really perfected please let me know! I am getting really tired of overheating/cooling.

Let's see if I can show the progression of my heat control testing. I've gone through 2 major setups, both had some modification along the way.

First round of modification: Blocking off direct steam heating from the boiler. In this version I put a plastic water bottle cap over the dipper tube and fit to the back of the pre-millenium group. This effectively stopped open steam migration between the boiler and the group, slowing the rate of heat transfer and stabilizing the group at a lower temperature than an open to boiler steam connection.

Here it is fitted to the dipper tube. The copper wire is used as a backstop to the plastic.

It worked well, but once heated up a few times the plastic cap did flex and open up more than I would like. At that point I picked up a stainless washer close to the size of the dipper tube, using a round file slowly filed it to be an exact match to the dipper tube. I used this as a backing to the plastic cap for a more rigid steam block.

Again, assembled on the dipper tube.


On the pre-millenium groups the dipper tube screws in deep inside the group.
If I were to make one modification of this it would be to make a small airhole in the plastic, and possibly lined up with one on the steel washer. It could be as simple as a filed down spot on one edge of both. This would allow for pressure relief when raising the lever and keep the plastic washer from popping out from the back of the group. Regardless, it worked well at stabilizing my group temperatures enough that I didn't need to cool the group once in 8 back to back shots. A couple of pumps and the thermometry would show I was up to temp and ready for a pull.

Next up: The millenium group adapter mod.

For this modification I picked up the threaded, back of group, dipper tube adapter used in the millenium models. It's an inexpensive part, so experimentation with this is cheap.
I turned it down with a drill and file to make a smooth surface fitting to the back of the pre-millenium group. Attached the dipper tube, but it didn't hold in place after 1 session and fell out.



I then cut 2 grooves in that adapter for tight fitting o-rings. Fit it to the back of the group and screwed in the dipper tube just as you would for a millenium group. To take pictures for this thread I notice that it pulls out of the group quite easily once the o-rings have compressed and formed to the grooves so I may have to put in larger o-rings in the future if this pops out too.




The initial warmup does take several pumps of the lever to move hot water into the group. With this modification I can heat the group up to around 100c and watch it drop to 90c over time. A few pumps will bring it back up, so when I'm filling the basket I give it a couple of pumps, fill, tamp, lock and pull. I'm running boiler pressure at 1.0-1.1bar range for these temps on the front narrow part of the group.

So far I can say I prefer the second mod with a water saturated group, and as long as it holds up I think I'll stick with that one. If it doesn't work out well in the end I will definitely go back to the plastic blocker backed by stainless washer and still be happy. The washer mod is quite easy, and I think anyone could do that.

As an aside, I think that a laboratory grade plastic plug with hole for the dipper tube shoved into the back of the group would likely work just as well for a saturated group mod. If anyone has those handy of the right size it might be worth a test if you are interested.

Looking at your latest mod you have effectively connected the above piston and below piston volumes together and terminated both below the nominal boiler min low level point. This has effectively stopped or markedly reduced the steam-condensate flow in the above piston volume when the lever is full down and at rest. What rpavils and I were thinking of was to keep these 2 regions hydraulically separate but terminate the above piston area below the nominal boiler min low level point. Right at the moment I think either would work fine. I suspect there may be some minor differences in long term performance and/or stability but what and how significant will require building one and actually monitoring performance. As the o-rings in your latest design bake in 250F water they will harden and shrink. The fitting may then be dislodged and that may happen rapidly or take a long time, don't know.

I have considered a few ideas in the past but have always been too scared it would pop out or break, land on the element and crack it while under pressure. Sounds dangerous

The element is made with copper casing in my case and stainless for some others. It's quite resilient, and I don't think you are going to crack anything.

If it pops out you'll know, as all you'll get out of the group is volumes of steam or steam condensate. Been there, done that.

OldNuc wrote:Looking at your latest mod you have effectively connected the above piston and below piston volumes together and terminated both below the nominal boiler min low level point. This has effectively stopped or markedly reduced the steam-condensate flow in the above piston volume when the lever is full down and at rest. What rpavils and I were thinking of was to keep these 2 regions hydraulically separate but terminate the above piston area below the nominal boiler min low level point. Right at the moment I think either would work fine. I suspect there may be some minor differences in long term performance and/or stability but what and how significant will require building one and actually monitoring performance. As the o-rings in your latest design bake in 250F water they will harden and shrink. The fitting may then be dislodged and that may happen rapidly or take a long time, don't know.

Yeah, I'll see what happens with the o-rings. It's a point of concern, but seems to be holding over the last few days so that's a start.
Lever movement may be a little smoother right now than with a steam heated group, but I can't really be sure about that.

I was thinking about keeping the group neck water heated separately, but after seeing the millenium group adapter decided it was worth a try to just use that. You could still modify that part further to use a steam or water heated group area without too much more trouble than what I already did. A hole slightly enlarged through the center of that adapter would allow the tube to screw into the normal point on the group, then you could either use that adapter as a steam limiter or a hot water group plug.

The group essentially works much like the millenium group, sans piston sleeve. Mixing cold and hot water in the group neck area.

Well not quite the same, that is probably the issue. I suspect the tying the 2 areas together is not going to catch it for most users. To be honest I am not having an insurmountable issue with the machine as built but I realize for what you are doing it is completely inadequate. As I have not spent much time thinking through the thermal hydraulics of this mod I have not started making parts to test out the idea as there are several approaches and they will have short term and long term results that will be different. I do not pull 8 shots in rapid succession and usually only pull 2 double shots back to back with a delay before the next round, then the machine should idle for at least 3 hours and not end up overheated. That is initiating the process with sight glass cold level at the very top of the glass.