I built a 3-PID lever group machine much as you described. It still operates much like a classic dipper lever with different temperature control methods.drH wrote: This is a cool idea. It doesn't seem too far off from what ACS is building with their dual boiler Vesuvius lever. That will have 3 PIDs; 1 for the brew boiler; 1 for steam boiler, and 1 for the cartridge heaters in the cylinder/group. On top of that the pump will deliver adjustable preinfusion pressure up to 5bar. You can see Dave Corby pulling shots on the prototype test bed if you search YouTube.
The difference between that and my proposed design is that the new design would operate closer to a saturated group because heat for the brew water and the group head would be from the same heat source.