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Sprung levers - How on earth do they maintain their temperature?


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Seeking the lever pros out there. I have been looking at some kind of lever machine as an upgrade to my E61 HX machine. I wanted a dual boiler, as you didn't have to cool the group with a flush, and it was more temp stable.

I have heard it repeated again and again - "Lever machines do NOT need to be flushed", "Just lock the pf and go"...

But how? 

As far as I can see, sprung lever machines are single boiler, running at 120C/1.1bar or so. How does that then translate to being able to preinfuse at that temperature, then make espresso without wildly hot temps? My non-expert reading suggests it's basically the same as an E61 HX machine but with a lever, but I would love to know more.

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3 hours ago, Hestu said:

Seeking the lever pros out there. I have been looking at some kind of lever machine as an upgrade to my E61 HX machine. I wanted a dual boiler, as you didn't have to cool the group with a flush, and it was more temp stable.

I have heard it repeated again and again - "Lever machines do NOT need to be flushed", "Just lock the pf and go"...

But how? 

As far as I can see, sprung lever machines are single boiler, running at 120C/1.1bar or so. How does that then translate to being able to preinfuse at that temperature, then make espresso without wildly hot temps? My non-expert reading suggests it's basically the same as an E61 HX machine but with a lever, but I would love to know more.

My understanding is that, in big levers, namely Londinium L1, LR, Bosco, a Profitec 800, etc the group mass is responsible to work as a temp stabiliser and heat sink. 
 

@dfk41 or @coffeechap may be able to tell you the proper explanation. 

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Yep, the boiler heats the water, which is then pulled into the warm, but not hot group which moderates the temperature as the shot is pulled. This process is the reason you don't leave a simple lever machine running for a long time, as the group will eventually come up to boiler temperature and be way too hot. It's why many La Pavoni's have heatsinks fitted to their groups to stop things getting too hot, and you see group thermometers so you can see when the group gets too hot (or cold in the beginning) for a good shot.

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@Hestuthere are many factors at play but essentially what @MediumRoastSteamhas said is right, the group in commercial lever groups has a large thermal mass and serves to dissipate the high temps of the water I. The boiler or hx (which runs through the boiler.

the pathways from boiler to group are tuned by the manufacturers to ensure the water is in the right temp range for espresso when it hits the puck.

however not all lever machines are the same, the Bosco (in my experience) requires a short pull of it has been idling for a long time, to bring the group temp up to the correct range ( it has been isolated further from the boiler by a reservoir) The londinium l1 ( precious model) is a boiler fed group but has a thermosyphon loop to regulate temperature which means you do just lock and pull. There are many HX pump machines like the Nota for example that employ a similar system which means you don’t have to flush that group either. All machines are not the same!

The LR24 is different as it is a cold feed HX into a thermosyphon so temp from the water in the HX is dropping before it hits the group where it is stabilised. Interestingly this means that with preinfusion pressure comes temp fluctuation that is repeatable so the higher the preinfusion pressure the higher the temp at the puck, this means you can adjust the temp to suit different roast profiles.

there are other lever machines in development for example a dual boiler Vostok one group (not sure when it will comes to market) which has separate boilers for brewing big and steaming and thus the temp at the group should be able to be tuned.

Even the small lever machines operated differently for example what seem like very similar machines (la pavoni and Cremina) behave very differently. Again the group on the Cremina is better isolated from the boiler so doeasnt over heat like the pavoni which gets very hot over time. 
 

hope this helps

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@coffeechap

Thanks for all the great info, sounds like some serious physics and engineering goes into these levers. I will be on the look out for one in the future for sure. 

I imagine if you restrict the flow of the thermosyphon in just the right way, and set the PID/Stat at just the right pressure, the group head just stays at a particular Temp?

It also seems like I have to take a very close look at what system of cooling/heating the lever group I actually want, as I am currently just leaving my HX on all day, and pulling a cooling flush before use. 

 

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I think it also depends on what coffee you use as well, noted by coffeechap. With my Bosco set to 1.2 bar I do not need to flush for a robusta blend I have, I just walk up and pull. However for a pure arabica roast I tried out a few weeks ago I did need to do a small flush to bring up the temp a bit that suited the roast appropriately.

My experience with an older thermosyphon lever, the Zodiac Group seen on machines like the Faema President, is also pretty hands free with the coffees I prefer as there is water constantly cycling through the groups to maintain a certain temperature besides the thermals from the group materials themselves. You can mod the thermospyhon loops with a valve to alter the water flow and with that the group temperature but I keep it stock. 

I am very excited to experiment with an earlier group from Faema that is also thermosyphon but different from the Zodiac so when I get my hands on the machine I can say more.

Edited by IamOiman
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