Hi Teme,
I'm just the final user, but you are lucky , i work in a power plant and i've a degree in thermodynamics.
You are right, if we know that Pressure x Volume = K x Temperature , we should imagine that there is a drop pressure when the volume increase.
But.. in the meantime there is an increase in the temperature due to the heater still on (in my case the flame).
I've seen a technical report which says that you have a variable pressure from 9.9 to 9.5 before opening the valve , and during the extraction the machine mantain the 8.5 pressure.
If you want more technical info, i will send you via pm mr. Bacchi email (you can easily find it on the web).

regards
Lucio

Lvx wrote: But.. in the meantime there is an increase in the temperature due to the heater still on (in my case the flame).
I've seen a technical report which says that you have a variable pressure from 9.9 to 9.5 before opening the valve , and during the extraction the machine mantain the 8.5 pressure.

Hi Lucio,

That makes sense, but I (apparently incorrectly) assumed that there would be no way that the temperatrre increase could take place quickly enough to maintain pressure. I guess that would depend on the kind of stove used - gas or induction and you might be ok, but a "regular" electric stove? I guess the small water volume and aluminium construction help here.

Anyway, quite an interesting "machine" albeit fairly impractical (especially for multiple coffees) and slow.

Br,
Teme