La Pavoni Europiccola stainless piston sleeve. - Page 2

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Eyal
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#11: Post by Eyal »

A couple of weeks ago i bought the stainless steel sleeve from coffee sensor for my beloved post mill europiccola.
Like posted above, this is one of the major upgrades one can make. The pull is as smooth as hell(or as heaven :D ) and i like that the grouphead heats up in a slower pace so i have more control and it reduces the chance that the grouphead will get overheated before i pull my shot. And maybe it sounds silly but the machine feels more solid to me, no more plastic. For me its important :)
Anyway i didnt want to open a new thread but i felt i must share my exprience for other pavoni members out there

LObin
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#12: Post by LObin »

I can't recommend this modification enough. It's a major upgrade to any post-millenium La Pavoni imo.

I've just finished a 2001 LPP rebuild and have opted for Coffee-sensor's stainless sleeve. Not only is the craftsmanship outstanding but the results in the cup have improved by a margin compared to my pre-millenium LP. Most noticeably when pulling straight espresso, light to medium roasts.

I'm attributing this to the superior heat stability of the gen3 group, and even more so with the upgraded SS sleeve. Much more temp stable during the pull vs the big declining profile of the gen2 49mm group (which is more forgiving though).

This picture speaks by itself...
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pizzigri
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#13: Post by pizzigri »

In my very personal opinion, respecting everyone's points of view and opinions, it is always wrong to mix in wet/hot environments brass and steel (stainless or otherwise). I believe this argument has been discussed before in much more problematic placements. i.e. stainless steel bolts on brass boiler rings for heating elements, but the issue still stands. There's different expansion coefficients (11.2 for brass, as low as 5.5 for SS depending on alloy), but also galvanic corrosion and stress corrosion cracking. I'm sure nothing is going to happen to the sleeve, in that location i believe it is safe - maybe some problems could arise in the event of disassembly of the sleeve many years down, or simply everything's ok. But why court a wrong concept? there are many machines that had problems due to incorrect SS/brass use (ECM comes to mind) so IMHO, if I were to replace a polymer sleeve, I'd use a brass one. My 0.2 cents
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LObin
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#14: Post by LObin replying to pizzigri »

There's an aftermarket brass sleeve that is also available.
I don't have extensive knowledge when it comes to metal chemistry but as you mentioned, the SS sleeve is very likely not an issue.
I personally have opted for SS since it's a safer material. It's never 100% clear if the modern brass parts in the food industry are lead free or not. At least not for the state of California ;)

From a study done a few years ago by Ruel "Bong" Juachon, the SS sleeve had by far the most stable temperature curve throughout the extraction, although I don't remember how different the behavior of the gen3 group with brass sleeve was.

I could also argue that my piston is made out of SS but then there's no contact with the sleeve walls...
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pizzigri
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#15: Post by pizzigri »

LObin wrote:There's an aftermarket brass sleeve that is also available.

From a study done a few years ago by Ruel "Bong" Juachon, the SS sleeve had by far the most stable temperature curve throughout the extraction, although I don't remember how different the behavior of the gen3 group with brass sleeve was.

I could also argue that my piston is made out of SS but then there's no contact with the sleeve walls...
Well, SS has a much poorer heat conductivity, so makes sense.
In regards to no contact, in reality, you do have SS to brass contact and in the most "problematic" place (in the sense of maintenance): the threads.

LObin
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#16: Post by LObin replying to pizzigri »

No contact between the stainless piston itself and stainless sleeve. Not between the sleeve and the group.
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drgary
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#17: Post by drgary »

pizzigri wrote: In regards to no contact, in reality, you do have SS to brass contact and in the most "problematic" place (in the sense of maintenance): the threads.
Franco, would this be mitigated by using food-safe anti-seize compound in the threads?
Gary
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What I WOULD do for a good cup of coffee!

bwren
Posts: 57
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#18: Post by bwren »

pizzigri wrote:In my very personal opinion, respecting everyone's points of view and opinions, it is always wrong to mix in wet/hot environments brass and steel (stainless or otherwise). I believe this argument has been discussed before i... ? there are many machines that had problems due to incorrect SS/brass use (ECM comes to mind) so IMHO, if I were to replace a polymer sleeve, I'd use a brass one. My 0.2 cents
What about SS piston rods with brass pistons - pretty much every Cremina 67 and LP, though I have seen some recent SS pistons.

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pizzigri
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#19: Post by pizzigri »

LObin wrote:No contact between the stainless piston itself and stainless sleeve. Not between the sleeve and the group.
Lobin, you're threading the sleeve in the group.
There is a very definite contact between the brass thread of the group and the stainless steel thread of the sleeve.
That is the contact i am referring to and where some, very minor, possible problem could arise.
The point I'm making is NOT that you WILL have problems. Far from it...
But, in good design and practice, all known points that could cause even remotely possible problems that can be avoided, should be - because, you're already going to be dealing with all those previously UNknown problems in the design that WILL come back to bite you in the... ehm.

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pizzigri
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#20: Post by pizzigri »

drgary wrote:Franco, would this be mitigated by using food-safe anti-seize compound in the threads?
I don't think so, because it's not galling we're looking at. I have no idea if the possible corrosion would make it difficult to remove the sleeve years down the line (which is the "problem" I see in my post above).