Lever espresso machines that do not overheat like La Pavoni

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zubinpatrick

#1: Post by zubinpatrick »

Could someone please explain how an Olympia Cremina group head does not overheat like a pavoni? Also as I really love levers, which other semi available lever machines out there have a group head that does not over heat a la Pavoni. All info much appreciated, Thanks Patrick.

mturkel99

#2: Post by mturkel99 »

Hey Patrick, the Olympia, while possibly more temp stable than the La Pavoni, will overheat. After a warming flush to heat up the group, and one shot, most of us let the group cool off - which means turning off the machine or soaking hte group in ice water - before pulling another shot. The Olympia Cremina, like the La Pavoni Professional, raises boiler water to steaming temperature (250F) and the group head leaches 50 degrees or so out of the water. Very soon, the group head cannot act as efficient a heat sink and the shot will taste bitter. Even the La Pavoni Europiccola will eventually overheat. There are a couple of temp stable lever machines (that are heat exchanging). For instance the Gaggia Achille.

roadman

#3: Post by roadman »

zubinpatrick wrote:...overheat like a pavoni? Also as I really love levers, which other semi available lever machines out there have a group head that does not over heat a la Pavoni. All info much appreciated, Thanks Patrick.
The group on a Cremina is bigger than a Europiccola and so helps stabilize the temperature. In this case, more brass = better stability. A properly adjusted Cremina will overheat eventually, but no where near as fast as a Pavoni.

Other levers use other means to stabilize brew temps. My experience with the other levers is limited to what I've read about them on HB so I'll leave others who are more knowledgeable to chime in with more info.

Jon

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timo888

#4: Post by timo888 »

zubinpatrick wrote:... as I really love levers, which other ... lever machines .... have a group head that does not over heat...
The Ponte Vecchio Lusso (available with one or two groups), a spring-lever, has a group that is not bolted to the boiler (i.e. no metal-to-metal contact) and so no heat is conducted to it; its only source of heat is convection, from pulling the shots and from a thermosyphon which keeps the group warm and stable.

Another alternative is the manual-lever Gaggia Achille, a heat-exchanger whose group temperature can be managed by the flushing of water.

Regards
Timo

Jarno

#5: Post by Jarno »

Oddly enough, I find that most of the heat that warms the grouphead, unless standing on for 30 minutes, is not from conducted heat from the boiler. It comes from the brew water with each shot. Of course, this is a problem with these single boiler machines (Pavoni, Cremina).

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timo888

#6: Post by timo888 » replying to Jarno »

I don't doubt what you say, but I think it is the combination of conducted and convected heat that is the real clincher. With a machine whose group receives both conducted heat and convected heat, you cannot simply wait for the group to cool down after pulling a couple of shots, because more heat is continually being conducted out from the boiler; the group gets heat-saturated and cannot sink enough of it away to put the shot in sweet territory (unless the barista becomes proactive and cools the group with a wet towel). On the other hand, with the Lusso, you can simply wait for the group to cool down, because its only source of heat is convection; if the group gets hot from pulling three or four shots in a fairly short time, the thermosyphon flow slows down automatically, because the rate of flow is governed by the laws of convection.

Regards
Timo

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peacecup

#7: Post by peacecup »

My experience with the La Pavoni Pro (pre millenium) was group heating from conducted heat was MUCH greater than it is on my Ponte Vecchio Export (also directly bolted to the boiler). By the time the boiler on the LP was up to temp the group would be hot to the touch. When the PV gets up to temp the group is still cool. I'm not sure if this is due to differences in the connection, or in the relative heat sink capabilities of the group. I do think the PV group is a better heat sink, more brass, and a greater surface area to volume ratio. Also, setting the pstat lower can increase the time it takes to overheat the group.

PC
LMWDP #049
Hand-ground, hand-pulled: "hands down.."

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mbach

#8: Post by mbach »

I'd like to see what clever methods people have for cooling the group those machines (like pavonis) that heat up. I've always thought an extra portafilter with cool water running through it between shots would work well.
mbach
LMWDP #037

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shadowfax

#9: Post by shadowfax »

I'll volunteer mine. I am actually anal retentive about cleaning my pavoni in between shots, so it heats up a lot faster than most, because I actually put a little piece of styrofoam in the filter basket to make it into a blind filter, and then I wriggle it around with the lever up to kick out the loose grinds... a method adapted from backflushing wriggles on E61 machines.

Anyway, when I want a second or third shot with the machine on, I usually just hold two ice cubes against the grouphead till they melt. I do this prior to distribution and tamping, so it gets a chance to recover a little. This seems to work very well, as I almost never see any kind of burn-ring from overheating, and the coffee is also rarely sour from being too cold. It certainly works for me, and it doesn't feel like it's too much work.

Sometimes I think, "wow, I'd really like an Elektra!" 2 minutes later, I think, "If I were going to spend that kind of money on a machine, I go all the way and get a Quickmill Vetrano." IMO, my vintage but near-mint $200 La Pavoni can contend with just about any machine on looks, and beat the crap out of ANY machine in terms of looks per dollar spent. It's more trouble to make shots, but it's also about 1/10th the trouble to clean and descale, not to mention to take apart and service. I really like the fact with these machines that a simple mind such as myself could explain every part of this machine to you. No black boxes under the base!
Nicholas Lundgaard

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GB

#10: Post by GB »

I have owned a PV Export for a couple of months and like peacecup's the group head is not immediately hot to touch after it gets to correct working temp. Also like peacecup, I think is in part due the group head's connection and resulting poor thermal conduction paths to the boiler:

1. Thru the brass screws and nuts which have a high thermal conductivity but the total area of conduction is only about 1 cm square
2. Thru about 1.5 mm thick teflon gasket which has a large surface area but has a very very low thermal conductivity.
3. Via the walls of the group head brass syphon tube which has a high thermal conductivity but a very small cross section
4. From direct contact with the hot water in the boiler, but the area is small probably < 0.5 square cm because the teflon gasket's inner diameter is only slightly larger than the syphon tube. (note. only true when the boiler is more than 1/2 full and the boiler water is in direct contact with the group head )

Thermal conductivities W/cm-K
Brass = 109
Stainless steel = 17
Teflon = .002
Water = 0.58
Steam = 0.016 (at 125 degrees Celsius)

Now, a crazy idea! If I changed the group head studs and nuts to stainless steel, made the teflon gasket a tight fit on the syphon tube, and changed the syphon tube material to stainless steel would it be worth the effort?

Cheers
Geoffrey
Simply coffee