Lever espresso machine designs - Page 2

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Zlobny_leshiy (original poster)

#11: Post by Zlobny_leshiy (original poster) »

Big thanks to everyone who answered my question. You helped me to build more confidence in using this design with a valve in the piston. I will add here CAD models when they are finished. Maybe you will have some suggestions about this concept.

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truemagellen

#12: Post by truemagellen »

The caravel is a great little machine but is very small basket, 45mm? and small shot volume. Which is why its not super popular. The strietman is 49mm and can deliver a very large shot. There is no risk of air in the shot due to the valve being in the piston as others mentions.

Part of my reason for owning the Strietman over the La Pavoni and the La San Marco (Izzo Leva) over other larger spring machines are these mechanisms which you are trying to achieve so I am very interested in what you come up with.

Good questions!!

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yakster
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#13: Post by yakster »

The Caravel remains pretty popular considering it's been out of production for over four decades.
-Chris

LMWDP # 272

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truemagellen

#14: Post by truemagellen »

I guess it's relative popularity. I think it's great, built like a tank.

If someone built a new one with 49mm I think it would sell really well too.

ira
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#15: Post by ira »

I was reading this post and it crossed my mind that one could make a manual lever with an isolated and electrically heated group and a small hose running from the boiler to the piston and use a pump to fill the group, stopping it when the lever reaches the fill level you're after. the main issue I see is keeping the water in the tiny hose warm, might need a second return line to warm it up for a second before starting.

Just a random thought.

Ira

pizzaman383
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#16: Post by pizzaman383 »

I have thought about some lever group design possibilities. I think the classic group head mounted via a flange and sitting in the open doesn't make sense, any longer, now that PIDs and cartridge heaters are so inexpensive and reliable.

My idea is a sleeve like the modern commercial lever groups use that fits inside a squared-off enclosed water jacket group head totally surrounding the sleeve/piston/spring assembly wirh cartridge heaters in each corner. The PID-controlled heaters would heat the water and the cylinder/piston so the group doesn't lose or gain heat during the shot. The water would be fed into the group water jacket through a thermoblock preheater that brings the incoming water close to brew group temperature.

Basically, this would be a saturated group lever.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

Zlobny_leshiy (original poster)

#17: Post by Zlobny_leshiy (original poster) »

Thanks everyone once again. I'm stuck with another question here. As we know most of pumps for coffee machines deliver us pressure of about 15 bars maximum. But considering flow rate delivered by the pump the pressure can not raise up to these values as coffee in the filter releases actually the espresso with some flow rate. Dealing with spring lever mechanisms we don't have any limitations in flow. It gives us all the pressure the spring supply with the unlimited speed. And once again - here's a thing. Along the piston travel the load of the sping drops most to the half of the initial value. With all of my attemts to calculate the needed spring I have now 14 bars at the beginning of pour and about 6 at the end. Does this problem significantly affect the quality of the espresso?

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yakster
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#18: Post by yakster »

The 15 bars max is mostly a marketing number based on the pump's capacity and doesn't reflect reality, AFAIK. Most machines are set up around 9 bars nominal max pressure via OPV and other mechanisms and some home spring levers such as the La Peppina typically only peak at about 6 bars max and taper off from there.

I know that some people have used double springs in some home levers to increase the pressure but not everyone really liked the added pressure in the cup. Higher pressure will give you more body at the expense of clarity so it's a trade-off.

Maybe browsing the Decent profiles (I don't know how to do this) will give you a good idea of some pressure profiles with discussions about their affect on taste.
-Chris

LMWDP # 272

Zlobny_leshiy (original poster)

#19: Post by Zlobny_leshiy (original poster) »

Thank you for your reply. It's now much clearer to me. I am actually tending to use double spring design so I will be able to remove the inner one to see the difference.

drH
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#20: Post by drH »

pizzaman383 wrote:I have thought about some lever group design possibilities. I think the classic group head mounted via a flange and sitting in the open doesn't make sense, any longer, now that PIDs and cartridge heaters are so inexpensive and reliable.

My idea is a sleeve like the modern commercial lever groups use that fits inside a squared-off enclosed water jacket group head totally surrounding the sleeve/piston/spring assembly wirh cartridge heaters in each corner. The PID-controlled heaters would heat the water and the cylinder/piston so the group doesn't lose or gain heat during the shot. The water would be fed into the group water jacket through a thermoblock preheater that brings the incoming water close to brew group temperature.

Basically, this would be a saturated group lever.

This is a cool idea. It doesn't seem too far off from what ACS is building with their dual boiler Vesuvius lever. That will have 3 PIDs; 1 for the brew boiler; 1 for steam boiler, and 1 for the cartridge heaters in the cylinder/group. On top of that the pump will deliver adjustable preinfusion pressure up to 5bar. You can see Dave Corby pulling shots on the prototype test bed if you search YouTube.