Lever machine design thought...

[mattwells]

Okay, I will preface this with a disclaimer: first, I haven't read all of the design threads we have had earlier (I tried to read one or two, but they were over my head) and second, this may have (and probably was) already done by someone, but not to my knowledge.

Another disclaimer - I don't own a lever machine, currently, but have been outbid for 2 different Cremina's now, and am trying my luck at each one that comes along (at least until another deal pops up - maybe a PV export).

So one of the main problems with lever machines is keeping the group cool. It acts as a heat sink so this makes sense. Lever design is (or at least my [limited] understanding of the Cremina is): pull up on lever, pulls up on piston, draws hot water into grouphead from boiler, push down on lever, forcing hot water out into the cup.

My thought: why not have a reservoir (like an HX machine) so that when you push down on the lever it draws cool water from the reservoir. That would cool the group and I doubt that the water would cool down the reservoir that much (especially if there was a switch that kicked the element on when the cool water started into the boiler).

A thought that came to me in the shower. I am sure that in the history of lever machines it has been done, but was it large scale? In production now? Did it work?

Pontifications from a lever-wannabe

/mw

[mbach]

So then when the shot is finished and the piston is at its low point, there is water above the piston cooling the group. Then, when the piston is raised again this water returns to its own (cool) reservoir and upon lowering returns? I like it. What prevents the cool water from heating up?
mbach

[timo888]

Cooling a group is far less exact than heating it because the temperature of the incoming cool water is an unknown. Is it 40°F? 60°F? 75°F?
Regards
Timo

[mattwells]

Cooling a group is far less exact than heating it because the temperature of the incoming cool water is an unknown. Is it 40°F? 60°F? 75°F?
Regards
Timo

True, but this would (theoretically) extend the number of shots a home machine could pull. Assume the cool water is at room temperature (or thereabout, probably a little higher since the reservoir would have to be somewhere near the machine). It wouldn't be precise, but shots from a lever machine are (at least somewhat) imprecise by nature temp-wise (or with my understanding of them it seems they would be).

mbach - Exactly the idea, but the cool water would be pushed into the boiler instead of back into the reservoir - that way the boiler wouldn't have to be refilled (you could draw the same amount from the reservoir as you are pushing through for the shot). The reservoir would be prevented from heating up the same way it is on any other machine - some form of isolation (have it sit next to the machine or insulated away from the boiler). If it was totally separate from the machine, that would allow you to keep the reservoir in the fridge, then pull it out when you wanted to pull shots (to increase the amount of heat it could leech from the group).

This would also allow the boiler to be refilled a la Gaggia Achille.

[timo888]

True, but this would (theoretically) extend the number of shots a home machine could pull. Assume the cool water is at room temperature (or thereabout, probably a little higher since the reservoir would have to be somewhere near the machine). It wouldn't be precise, but shots from a lever machine are (at least somewhat) imprecise by nature temp-wise (or with my understanding of them it seems they would be).

mbach - Exactly the idea, but the cool water would be pushed into the boiler instead of back into the reservoir - that way the boiler wouldn't have to be refilled (you could draw the same amount from the reservoir as you are pushing through for the shot). The reservoir would be prevented from heating up the same way it is on any other machine - some form of isolation (have it sit next to the machine or insulated away from the boiler). If it was totally separate from the machine, that would allow you to keep the reservoir in the fridge, then pull it out when you wanted to pull shots (to increase the amount of heat it could leech from the group).

This would also allow the boiler to be refilled a la Gaggia Achille.

The Gaggia Achille boiler is not being refilled by any lever action, BTW. The water from the cold water reservoir is gravity fed into the piston chamber. On the piston upstroke, the water actually flows through a channel in the piston assembly down into the lower chamber below the (now retracted) piston head. On the piston downstroke, the water is pushed out of the piston chamber and into an HX tube that runs through the boiler, and from there out to the puck. The boiler has to be refilled manually.

The problem with cooling the group is that the group gets cooled before it needs to be, resulting in cooler-than-desired espresso on the early shots. Perhaps not as bad as scorched espresso. But less than optimal. If you're going to have a pressurized boiler which produces both brew water and steam, probably the way to go is to heat an indirectly attached group with a thermosyphon, and to lower the p-stat so the pressure is adequate for steaming milk for several cappas but not so hot that the group cannot sink off the excess heat after several shots. (This is how the Ponte Vecchio Lusso works.) A fancy version would let you adjust the thermosyphon flow, to compensate for adjustments to the p-stat.

Regards
Timo

[mattwells]

The Gaggia Achille boiler is not being refilled by any lever action, BTW. The water from the cold water reservoir is gravity fed into the piston chamber. On the piston upstroke, the water actually flows through a channel in the piston assembly down into the lower chamber below the (now retracted) piston head. On the piston downstroke, the water is pushed out of the piston chamber and into an HX tube that runs through the boiler, and from there out to the puck. The boiler has to be refilled manually.

Meant to say the reservoir - it could easily be refilled like the Achille's.

The problem with cooling the group is that the group gets cooled before it needs to be, resulting in cooler-than-desired espresso on the early shots. Perhaps not as bad as scorched espresso. But less than optimal.

It seems that you could use a few pumps through the machine to equalize the heating/cooling. That would give more predictability. But then, you might as well go with the Achille's traditional HX set-up.

[happytamper]

Hey Mattwells,

Sounds like great idea. It would be hard to be exact with the temperature but it would definitely help to pull more shots consecutively on the smaller machines such as europiccola. Yet I think most owners of these machines rarely pull more than three shots consecutively on a regular basis. But what a cool thing to have. Sounds fairly simple too, lowering the piston some cool water would be sucked into the chamber above the piston head and when raising the piston this water now heated (therebye cooling the head) would be expelled into the cool water reservoir. Pretty chill, As my son would say and may be appropriate here.

So when will the mod be available?

I think a simpler idea would be to have a different dedicated tank for steaming and the grouphead could be gravity fed by a separate tank of water kept at the right brewing temp. Is this the design that the beast uses? Perhaps a whole different unit for steaming. Yet I find letting the superheated water preinfuse the puck at a small pressure before pulling the shot creates a different mouthfeel and taste. Also seems to make for a more solid puck after the shot is pulled. Hence the different espresso made by the La peppina from the La pavoni.

[timo888]

I think a simpler idea would be to have a different dedicated tank for steaming and the grouphead could be gravity fed by a separate tank of water kept at the right brewing temp. Is this the design that the beast uses? Perhaps a whole different unit for steaming. Yet I find letting the superheated water preinfuse the puck at a small pressure before pulling the shot creates a different mouthfeel and taste. Also seems to make for a more solid puck after the shot is pulled. Hence the different espresso made by the La peppina from the La pavoni.

Yes, the Beast would have a dedicated unpressurized brew kettle with a conduction-heated group directly below it, and a dedicated steam heater (either pressurized boiler or thermoblock). Keeping brew and steam production separate does simplify the thermal situation (while complicating the electric situation).

Since Peppina's spring is no behemoth, the right preinfusion makes a big difference in the extraction. The Peppina's spring and 52mm piston chamber (45mm basket) produces ~6bar, based on the calculator at efunda. Judging from the high frequency of emoticons in your postings to Alchemist's pressure gauge mod thread, I suspect you're pulling shots on the Pavoni at fairly high pressures, Mitch. 9 bar minimum. That might account for some of the difference in the mouthfeel, although a hot blast of Pavoni boiler water must make a contribution too.

Regards
Timo

P.S. You haven't said a peep about the Arrarex for some time. What has become of the Little? The Caravel is often my machine of choice when I want to experiment with different temperatures on a new roast. Ever since I replaced the o-rings, it is capable of generating good brew pressure without the spluttering.

[happytamper]

Hey Timo,

Yes, the Caravel little. Embarrased to say that is sitting pretty on a shelf in my kitchen awaiting an adapter plug that will fitting into my 220 volt transformer. I keep forgetting to look for the adapter so it has alas not been used yet

And I simply enjoy all the emoticons. . I will post a followup on the pressure mod today