jimskelton wrote:in theory, if the boiler is pressurized to .8 bar, the water temp will be around the 240-250 range.
Yes, that is roughly correct. At 0.8 bar gauge at sea level (1.8 bar absolute), water boils at about 241F, and at 5000ft altitude, (where 0.8 bar gauge is only about 1.6 bar absolute) at about 236F.
jimskelton wrote: Or is it engineered to dissipate heat fast enough to lower the temp to the ideal 200 degrees by the time it reaches the portafilter?
That's the idea. In the La Pavoni, the engineering to try to achieve that has gone through a couple major changes over the past 40 years.
jimskelton wrote:If this is the case, if you pull shots too frequently, does the temp rise too much?
Yes. Is a well known problem, especially in the machines that don't have a sleeve inside the cylinder. Pavoni recognized this and went back to an earlier design with the "Millennium" group (introduced in ~2000). This group lets the hot water feed into the space inside the brass group but outside a plastic cylinder that is the brew chamber. When the lever is raised on these the water that has already been cooled somewhat by the group enters the brew chamber. The space inside the group and outside the brew chamber, with the lever fully raised, accommodates about 40 ml of water (I measured it - I'm such a geek.)
jimskelton wrote:If anyone has temp data from one of these machines I would be interested in seeing it.
Me too, just because I find engineering problems interesting. I would really love to have a long conversation with a couple of old timer design engineers from Pavoni at a nice coffee bar in Milano. I'll need to learn Italian. But I'm not sure that analysis and reverse engineering are of that much practical use in pulling a good coffee from these things.
jimskelton wrote:I can see that pulling some water through the group is necessary to warm it up since the group is suspended away from the boiler.
The Pavoni group is bolted to the boiler, and on some vintages ('74-'00) also has a vent between the top of the brew cylinder and the boiler. They will come up to temp (even above desired temp) if left on long enough. Most people leave them turned off until they are wanting a coffee because they can be ready to pull in only 5-10 minutes. Group-warming flushes are fast and effective, each little flush can warm a too-cool group by 5 degrees. There are tons of home remedies for cooling the group when necessary (cool portafilter, Orphan Espresso's third shot gadget, cool wet towel, putting a ramekin of cool water at the group and lifting the lever, etc.)
If you have a pStat Pavoni and it doesn't run 0.8 bar, don't fret - Pavoni's specs (http://www.lapavoni.it/PDF/CAT_LEVER.pdf
) indicate that the pStat's of the current machines are set in the 0.7-0.8 bar range. I think lower is better provided you're steaming well enough. With a gauge and an on/off switch you can have the best of both worlds - brew at a low pressure then turn it back on for powerful steaming.