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Topic: Changing the piston in my Europiccola/thermodynamics question (6 msgs / 192 lines)
1) From: Derek Bradford
Hi All,
Since I'm ordering a new lever for my Europiccola, I've also been
wondering (for a few weeks now, actually) about changing my piston.  I
have the Millennium model, which has a plastic piston.  There is a
brass replacement available, and after using my brass-pistoned
Elektra, I wonder if putting a brass one in my Pavoni would be a wise
move.
My question really centres around heat.  The new Millennium model uses
a plastic sleeve to insulate the water in the group from the group
(which is attached to the boiler, and thus quite hot).   I wonder if
the plastic piston in the machine is designed to work in conjunction
with the plastic sleeve, or if the decision was more based on cost.
Given some of the cheaper components used in the new Millennium, I
suspect it has more to do with cost.  Since the piston never comes in
contact with the group; only the gaskets actually touch the sleeve,
would anyone suspect a brass group of making the group water hotter
than with a plastic piston?
Thanks in advance,
--Derek
-- http://www.novernae.comHome of the Wandering Sloth

2) From: Tom Ulmer
Hi Derek-
(a) Is there a problem with the Elektra piston?
(b) I wouldn't think the water would need isolation from the group. 
(c) Yes there is a design factor and yes there is probably cost
considerations.
(d) The group by being in contact with the boiler will dissipate heat to its
environment. I would tend to think there would be heat isolation between the
group and the boiler to improve boiler efficiency. Brass has the ability to
conduct heat much better than plastic.
Of course there is a good likelihood I did not understand the question(s).

3) From: Derek Bradford
On 10/26/06, Tom Ulmer  wrote:
<Snip>
Actually, I was just using the Elektra as a comparison.  It's my
Pavoni Europiccola that I'm having replaced.  No, there's no problem
with it, although I am concerned that flavour and odour are being
absorbed.  The shots on my Elektra had a more complex taste, and I
wonder if a stained piston couldn't be a culprit.
<Snip>
With a Europiccola, it does.  Because the group is physically
connected directly to the boiler, it gets extremely hot; the machine
will overheat after only a few pulls, and then it must cool down.  By
adding the insulating sleeve inside the group, they've managed to
lengthen the time you can pull shots for before it's overheated by a
shot or two.
<Snip>
Here you've hit the nail on the head.  Heat will dissipate more
readily to brass and water.  The water (and consequently the brass
piston) is isolated from the group by the sleeve.  However, the piston
will hold heat better, and so could do one of a couple things: it may
retain more heat, thus lowering the number of shots before the machine
overheats, or it may maintain a more stable temperature at the filter
screen and give a more stable shot.  It certainly won't absorb odours
and oils.
I'm leaning toward buying the brass piston.  I need to do a gasket job
on the machine; a few are starting to go, and buying a set of piston
gaskets is half the price of a brass piston, which comes with gaskets.
 And I'll always have the old piston...
I just don't like the idea of plastic pistons.  It feels cheap and wrong.
Thanks for your help.
--Derek
-- http://www.novernae.comHome of the Wandering Sloth

4) From: Walter
Hi Derek,
I think that Pavoni used the plastic pistons only for a few years, I 
have heard that the more recent models come with the brass piston again.
A few months ago I have replaced the plastic piston in my 2003 
Professional with the brass one and I have not noticed a change in taste 
or behaviour after that. Generally, overheating is not much of a 
problem, with the Pavonis. If you want to make more than 2 (or 3) shots 
in a row, just have her "drink" some cold water in between and rinse the 
portafilter, wait until the group is at temperature again and all will 
be well...
Cheers,
Walter
Derek Bradford schrieb:
<Snip>

5) From: Derek Bradford
On 10/26/06, Walter  wrote:
<Snip>
That's a shame.  If that's true, I just squeaked in at the end.  I
bought mine last year.
<Snip>
What made you decide to change the piston?
 --Derek
-- http://www.novernae.comHome of the Wandering Sloth

6) From: Walter
Derek Bradford schrieb:
<Snip>
I bought mine last year too. Only when I opened it I realized it had 
been built in 2003...
<Snip>
Curiosity mostly ... after someone had recommended it in another BBS. 
And the fact that I spotted some sort of a hairline crack on it (which 
in retrospective might have been a scratch as well)
Walter


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