Puck suction / fracturing in levers

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grinser

#1: Post by grinser »

i own a europiccola and used it every day (until recently where i started experimenting with a microcimbali )

on the europiccola, i used the technique of lifting the lever partially before inserting the portafilter, to not suck up the puck or fracture it. then I did a small fellini to get around 30g out of 12.5g in the basket. in know, the fellini move is controversial, but i started to ask myself why, and even questioned why i was lifting the lever partially before inserting the portafilter.
the piston seals on the europiccola are "V"-seals, so they should let water through one way (from the point where the upper seal passes the inlet port).

Also, when looking at how commercial levers are built, the arrangement of the two lower seals (for example on the bosco/CMA group) is similar to the seal arrangement on the europiccola. but i have never seen someone pulling the lever partially on a commercial lever or even recommending this.


(both pictures taken from this forum)

what is it that i am missing? why is the partially lifted lever a sometimes recommended practise for the europicoola but not for commercial levers?
(the microcimbali is out of this question at the moment since the newer models have o-rings as piston seals, wich i also find somewhat questionable)

mborkow
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#2: Post by mborkow »

Partially lifting the lever before locking in the portafilter is just so some people feel more involved in the process; I don't think it makes any difference at all.

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baldheadracing
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#3: Post by baldheadracing »

Lifting the lever in a Europiccola has, it seems, two different forms:

- the "original" method is to lock in the portafilter just as water is entering the group. Timing is key. If done right, then this will reduce the size of the air pocket between the bottom of the piston and the top of the water resting on the puck. If done perfectly, then the air pocket itself will almost disappear. (See also airbuster/valve mods for Pavoni's, and the bleeder valve in the Argos.) Reducing the size of the air pocket results in greater shot volume. The method may also change/flatten the brew temperature profile in machines that have brass pistons. You don't see this being done with commercial groups as there is a powerful spring to worry about when doing this manoeuvre, and commercial groups typically have enough shot volume without needing to do this.

- the other, more "common" method is to lock in the portafilter before water enters the group. When the Europiccola's piston is raised, then air is drawn upwards through the puck in the portafilter basket. If one aggressively raises the lever with the portafilter fully locked in, then the air drawn upwards could possibly suck the puck upwards, possibly leading to side channeling. The exact same thing can happen in commercial levers, but overcoming the force of the spring naturally slows down how quickly people lower the lever (raise the piston) at the beginning of the stroke.

I don't do either anymore. I just move slower as I get older :D.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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peacecup

#4: Post by peacecup »

Fwiw, the puck in this photo was subjected to two "Fellini" preinfusions before the shot was poured. I always supposed this to be a method to actively preinfuse instead of using boiler or line pressure. For me, such active preinfusion gives the best results and almost never results in messy bottomless pours, which would suggest puck fracturing.
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Hand-ground, hand-pulled: "hands down.."

Marcelnl

#5: Post by Marcelnl »

Just out of curiosity, did anyone ever investgate the air resistance of a dry puck?
I somehow expect it's low, especially given the fairly large diameter of a puck and low height

interesting footage, guess someone already thought this through ;-) ;
LMWDP #483

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mrgnomer

#6: Post by mrgnomer »

I think if the piston seals make a tight seal in the cylinder then pulling up with a loaded portafilter locked into springless creates enough of a vacuum to pull up and disturb the puck. Locking in just at the vacuum apex before water flows helps keep the puck intact.

On a springed lever I find the opposite happens. Starting from the top compresses the puck on the way down. I get fines sometimes in the cup before the extraction that must have slipped through the portafilter when the piston was coming down. Compressing the puck probably disturbs it some but not as much as pulling it up off the basket and dropping it back down.

After dosing down a bit and using a basket filter screen with my Europiccola the extractions improved. More even and the pucks are dry.
Kirk
LMWDP #116
professionals do it for the pay, amateurs do it for the love

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pizzaman383
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#7: Post by pizzaman383 »

With my spring lever I started locking in the portafilter right before the water started flowing into the cylinder. This resulted in less channeling and more consistent espresso.
Curtis
LMWDP #551
“Taste every shot before adding milk!”