Turn the boiler upside down with the heating element removed. Close the holes that are now on the bottom. Drop in a heating element and temperature probe for pid control. Attach the construction to a solid frame and put on the group. Put a water funnel or cap on top. That's it, I think:
a low cost, temperature stable, gravity fed manual lever with available parts.

As the topic says, just an idea. I'm probably missing something and water would be gushing out of the group!

This is the basic concept of other open boilers like Caravel and Peppina as I am sure you probably know. It would definitely be interesting. The only thing I see as a concern is temperature stability may go to the opposite extreme since the grouphead is much more massive than Caravel and Peppina. It would likely idle low and it may be difficult to hit the target temperature through heating flushes. This is just speculation so if you have the time, patience, and money, give it a try! I'd love to hear how it works!

Much easier to PID a Pavoni without all that rebuild, isn't it?

I contemplated something along these lines. I think the best route might involve chopping up two La Pavoni boilers and then TIG welding them back together in such a way so that you basically lengthen the boiler and also relocate the head down below the water level.

You'd end up basically with a taller boiler. I think you might also have to think about some sort of wall mount, so that you could avoid having the Empire State building on your counter top and also to aid with getting the cup under the group head.

If the double boiler idea makes it too long, then you could also just cut a normal boiler and TIG weld the top part to the open end of the boiler, then weld the threads to the other side.

I'm currently adding a milling machine to my garage (which is going to require restoring), so that's going to consume a lot of free time over the next month or two. But after that, I'm going to look into getting a TIG welder and a plasma cutter. I'll be looking for projects to weld, so if you have a La Pavoni you want to donate, I would be happy to take a stab at it for ya. Since doing the PID upgrade on mine, I'm pretty familiar with how they go together, etc.

Not sure about running it as an open boiler, but who knows.

Ray

Makes great sense welding two boilers together!

Myself, I'm slowly putting two old Europiccola's back together and will try the upside down boiler while doing that to test the group behaviour. I think I could donate some boilers later on if you want to weld them.

But you seem to have more plans... maybe you should start a line of exclusive, next-lever home levers. You have the insight in technique and a feeling for estethics. You're a great communicator and you know coffee. A bit like the direction Orphan Espresso took with their grinders.

You could use heat pipes to keep the group up to temp or at least keep the temperature difference from group to tank suitably low. I think your best bet is to salvage those from PC coolers. A separate group heater would be a suitable option too, but then you'd need multiple temperature controllers.

Most gravity-fed levers home some device to keep the grinds from coming back into the boiler. The Caravel is a marvel of design in that regard, yet it still allows a little backflush in. The good news with it is that the boiler is just a stainless-steel kettle that can easily be removed and rinsed. Ingenious design.

The miniGaggia is the simplest - the boiler sits directly over the portafilter, so the boiler temp is exactly the brew temp. But it sucks a lot of coffee back into the boiler, and is more difficult to clean.

Of course it would be fun to try an upside-down Pavoni - you'd have to figure out how to get the group hot enough though, contrary to the normal problem of keeping it cool. It would most certainly suck coffee back into the boiler as the group filled, so it would be best to have an open top to make it easy to clean.

PC

KurtAugust wrote:Makes great sense welding two boilers together!

Myself, I'm slowly putting two old Europiccola's back together and will try the upside down boiler while doing that to test the group behaviour. I think I could donate some boilers later on if you want to weld them.

But you seem to have more plans... maybe you should start a line of exclusive, next-lever home levers. You have the insight in technique and a feeling for estethics. You're a great communicator and you know coffee. A bit like the direction Orphan Espresso took with their grinders.

Well, thanks very much for the nice comments

I'm currently in the middle of restoring a milling machine, but I have giving some thought to making either a hand grinder of some sort and/or maybe some kind of very small foot print espresso machine or something.

Right now, I'm still tooling up the garage

Ray

Add an extended tank with lid that threads into the existing top opening - no need to modify anything on the stock machine other than temp control?

I call it FRANKENVONI!

A quick experiment to end the day. Just improvised with stuff lying around. Just to see how wrong I was with my original idea and forget about it.

Well, those shots ended up not being bad. Not bad at all... (certainly not for what was a half hour joke)

Some observations:
-To my surprise, the boiler leaks surprisingly little. Even with everything installed as it should. The pressure relief valve leaked a bit, but certainly doable (I was working above a sink to be sure). But what do you expect from an iron ball pushed again a hole with a flimsy spring.
-Preinfusion fails. The water trickles down so slowly, I had to do 5-10 Fellini's to wet the puck.
-Crema wasn't as much as with normal preinfusion at 0.7-1 bar.
-Worked ok without dipper tube.
-With boiling water put in the boiler and flushing, the temperature strip on the group head indicated a constant 85C/185F while pulling the shot. Too low, but not dramatic. The group idled at about 70C/158F. I was not using an extra heater to keep the water hot, I think hitting the mark would have been very possible otherwise.
-Being able -for once- to keep flushing is so much fun!
-Getting more shot volume once the puck was soaked was quite easy. Just an extra pull. No early blonding.
-My base happened to be a couple of wood blocks, which turned out to be good, because the lever handle obviously goes down lower than usual.

The blend was 50% Brasil Isidro Pereira Peaberry and 50% Ethiopian Yirgacheffe at 15g. Much to my own surprise, those shots were damn tasty. Yes, the roast was very fresh and I was probably just flabbergasted, but I just reached for the grinder to make another one.

Note: yes I admit using a bicycle tire.