I got answers to some of these questions from Lelit (through Jim at 1st Line). I believe this information refers to the final production model, which they're going to start building next month.
-The e-61 head is custom. The mechanical preinfusion feature has been disabled, so it doesn't interfere with the electronically programable, pump-driven preinfusion.
-The pump is a rotary pump, not a gear pump. Lelit says the preinfusion programming allows you to program how long the pump is on, and then the time the pump pauses before final infusion starts. I've read speculation (not confirmed by Lelit) that during preinfusion, the pump pulses, to keep the average flow rate lower than normal.
-This programable preinfusion can be turned off entirely. You have the option of using no preinfusion, or doing it manually with the paddle, Slayer-style.
-The paddle operates a needle valve, and gives continuous flow-control from full blast to zero. Technically speaking, as discussed in this thread My long and rambling path to preinfusion/pressure profiling
, the machine is flow-profiling rather than pressure-profiling. After the brew head is pressurized, the difference is somewhat academic, but during preinfusion the difference is significant. The flow-profiling approach should allow a very long, slow preinfusion and a corresponding extra-fine grind, to accommodate light-roasted single-origin beans.
-Most of Lelit's videos show the paddle being used to taper the flow at the end of shot, possibly to mimic a spring lever machine.
-Boilers are stainless and pipes are copper. Lelit's literature says the steam boiler is 1.5L, the brew boiler 800ml, each with a 1400W heating element. Possibly the 120 volt version will draw less juice. In either voltage, the electronics would have to keep both boilers from firing on full at the same time.
-Other features ... shot clock, steam boiler shutoff, programable "standby times" [is this wake/sleep?], PID settings for brew and steam, total and partial dose counters [no idea what this is].
I'm inhaling information about this machine because it's almost exactly what I've been looking for. The design principles of the Slayer appeal to me, but the price doesn't. And it's seemed all along that the Slayer's defining feature (manually controlled slow preinfusion) is separate from what makes it expensive (handmade, high-end, boutique everything). So I was hoping someone would catch on and make a machine for commoners with a similar super power.