lino wrote:I do like the idea of a simple, "modern", la peppina, or mini gaggia. I've toyed with some ideas for the simple setup.
Open boiler is ideal in my opinion. Though I would add a PID to it so that it makes temp conrol simple and precise.
If the boiler sits right over the group opening, like the MicroCimbali, then there is very little temp loss out the group.
If physical placement of the grouphead, elements, boiler size, and control sensor were "nailed", it would likely be a very stable, simple group.
To improve upon MiniGaggia with some of Peppina's features:
The group is shaped roughly like a Coca-Cola glass drinking rim side facing down.
The bottom of the Coke glass, i.e. the top of the group, protrudes into the boiler.
b o i l e r
------|'''''''|---------
The top of the group (the bottom of the Coke glass) is ~11mm thick and it has a male thread around the outer perimeter onto which the piston cylinder will screw down.
The top of the group has a ring of holes drilled through it (like Peppina) for water to flow through down from the piston cylinder. At centerpoint, the underside of the group 'cap' is tapped for a small setscrew which is to hold a one-way washer in place.
SPRING
{.....P I S T O N ......}
|..............................|
O.......O........O.......O ingress water holes in piston chamber wall
|.. piston chamber...|
|..............................| Bottom of piston cylinder is female threaded to fit over group cap
|===o====o====| Male threaded brass 'group cap' with ring of port holes from piston chamber
(.....____+____...) | _|+|_ one-way washer held against underside of group cap by a set screw
( ............................) .. ^ group collar is bolted to the underside of the boiler
(G......screen........G) shower screen held in place by a gasket (G)
(.............................)
The shower screen is held in place inside the group collar with a retaining gasket rather than a set screw.
To replace the one-way valve, simply remove the shower-screen gasket and shower-screen, and voila. There exposed to view from below is the set screw and the washer.
58mm group versus 51mm: 58mm gives a shorter piston throw (shorter piston cylinder is possible) making for a slightly shorter machine. But the machine could be temperature-stable even with a smaller group because the group and boiler are integral.
The top of the group which protrudes into the boiler should be well away from the calrod. The group could be brought up to temperature with a flush, like the S1. With group heated only by contact with boiling water there'd be little or no worry of overheated group even on the un-PIDed base model.
Regards
Timo
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