Tex
The Achille piston is plastic but not brittle type of plastic and it is not the weakest link of the machine. The cylinder (pos.17 on the diagram you’ve supplied) is made of a brittle plastic. Yes, the piston works on the cold side of the brewing path – it pushes cold water through HX to brew head. The design is very cool (unfortunately implementation is not). The weakest link is gasket (pos.16) that seals the cylinder to dome connection. It could be beefed up (quite tricky to install) but then the one way valves (pos.45-47) becomes an issue. On my machine I reinforced them but then cylinder cracked and that was the end of the road.
Now my Achille is up for grabs as spare parts (sans the cylinder).
I couldn’t compare shot quality to any other lever but my Brewtus III (that replaced Achille) has not treated me yet with the same ‘Awe’ factor as Achille did. Obviously the problem lies on the ‘other end of the portafilter handle’ and I had used them for a year (each) and with the same grinder. Brewtus provides more consistency and convenience though.
I only had two weeks to play with my friends Achille, and he wouldn't let me tear it apart. That's the same plastic piston used in pre-Millennium Europiccola models. Since they're not subjected to heat in the Achille, they might not break - but I've seen three LP's that've had their pistons broken, including one of mine. Fortunately, Parts Guru has the brass replacement piston for not much money.
What I don't see in the diagram is the HX itself - how large is it & how's it positioned in the boiler?
