Dreaming up a fantasy lever espresso machine - my take

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John Michael Hauck

#1: Post by John Michael Hauck »

So I've been dreaming again. I have spent a fair amount of time studying (and I hope to some extent understanding) the La Pavoni lever machine. From looking at the various alternatives out there (from Cremina to Flair to Kavei) I think there is room for some more innovation. I like frothed milk so a boiler is part of my dream.

Lever machines (with boilers) have a piston that opens over the coffee grounds (Kavei exception noted). This means there is a lot of trapped air to deal with when filling with water (see posts by Pat Moore and Dr. Pavlis on Flash Steam). As a result, there is a tradeoff between temperature and trapped air. That is the cooler the brew water, the more air remains trapped. This then nudges some lever machine users to brew at a temperature a bit hotter than ideal for extraction. My dream then includes a lever that pumps the brewing water - but is not located over the group head. It also includes a valve that can direct the water from the pump. So here is what I have come up with so far:

The first two illustrations below show the boiler, the pump, the brew valve, and the group head. The top illustration shows the brew valve pushed in and the bottom illustration shows the brew valve pulled out.

In both cases, when the piston in the pump is raised, hot water from the boiler passes into the area under the piston. When the piston is lowered, water from the pump is forced towards the brew valve. The two check valves ensure the water always flows in one direction: into the pump from the boiler and out of the pump to the brew valve.

​When the brew valve is pushed in, water from the pump is directed to the bottom port of the group head. The water exits the group head and empties back into the boiler. It is easier to see the path the water takes in the group head cut-away picture (third picture below). Also when the brew valve is pushed in, water in the portafilter area of the group head is opened to the drain.

When brew valve is pulled out, water from the pump is directed to the portafilter area of the group head. The other two paths in the brew valve are plugged.

Brew valve pushed in:

Brew valve pulled out:

The heating path in the group head:

A close up of the brew valve:

I then smashed it all into a box:

And gave it a face:

What are your thoughts?


#2: Post by pham »

Nice design.

Another simpler way to approach this is the way that Felice Aroso designed his machines. The Faemina fills the piston chamber with a one-way valve with water above the piston, so there is no air pocket when the piston descends. It has a pressurized boiler that steams, as well. IME, shot volume in that machine is independent from temperature, I get the same volume whether my group is at 80C or 95C.

The Peppina also has a one-way valve which is gravity fed by an open boiler with an upside down piston. If I wanted steam and more temperature control, I'd probably just add a small steam boiler to a Peppina like design instead of modifying the hydraulic path so heavily

John Michael Hauck (original poster)

#3: Post by John Michael Hauck (original poster) » replying to pham »

Thanks! I'm somewhat familiar with how the Peppina works (just from reading, not using). I passed over looking at the Faema since it is spring lever. Is there a resource that explains in a bit more depth how the Faema works?

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#4: Post by truemagellen » replying to John Michael Hauck »

The Peppina produces an excellent shot. You do pump it at the start then let the spring take over.


#5: Post by ojt »

Yeah! How about a "flash brew boiler" I think it's called that would heat the brew water above the piston, then a one-way valve from that to under the piston. I'm not mechanically versed so the details escape me but then you'd have to think how does the water end up into the group head, perhaps without a pump even, be in low enough temperature, and still be able to steam. With one boiler perhaps a utopy.

John Michael Hauck (original poster)

#6: Post by John Michael Hauck (original poster) » replying to ojt »

I believe that is what the FE-AR La Peppina does (Taking Down A Peppina).


#7: Post by ojt »

Yes, and Strietman CT-2 and others. But they don't steam :) I'm thinking along the lines of a saturated group but with a lever, and steaming capability. Perhaps there's a reason such a thing does not exist :)


#8: Post by mwynne »

More from the end user side than the internals... Lever placement (especially depending on intended pressure) might be a bit iffy - the handle looks real close to the controls/portafilter/cup. I'd be a bit nervous if anyone needed two hands to pull the lever (or is just clumsy like me). Probably less of a concern if it's a spring group, though.
LMWDP #673

John Michael Hauck (original poster)

#9: Post by John Michael Hauck (original poster) » replying to mwynne »

Thanks! This is not a spring lever, so your concerns remain. I'll add a concern about hitting my knuckles on the drip tray when finishing the pull.


#10: Post by mwynne »

It's a delicate balance between keeping it compact and keeping hands away from hot spots and edges!

Longer lever would help to some extent, but then size is affected. Lever mounted above the machine also would help, but you'd lose the compactness. Maybe offsetting the grouphead more to the left?

Would you have any concerns about stability with the lever set off center? If not on a normal shot, what about when someone chokes the machine and needs extra effort to pull the shot before removing the portafilter?
LMWDP #673