The red thing is the pressure sensor, Swiss made, very expensive but super reliable. It reads the pump pressure and is isolated from the rest of the system by 2 1 way valves. This is to prevent pressure interference
Nuttybarista I tried adjusting the preinfusion via the touchscreen and this seems to work! However, there is a discrepancy between what the screen says and what the pressure gauge shows. Pressure gauge PI pressure is 1 bar lower than I dialled in on the screen.
This is because the sensor reads the pump output pressure and prevents it going above the desired preinfusion pressure e.g. the push of the pump. In the group of course the pressure might be slightly lower as there is potentially flow into and out of the coffee puck. It’s unlikely to read the same…unless it’s against a blind filter (don’t try it). If the puck it relatively non permeable, it “might” right the end of the preinfusion read the same pressure very briefly. If you think about it though, the second the sensor sees 2 bar, it will stop the pump and at that moment if even 1 drop moves into the puck, the pressure will drop to nothing (until the pump runs again), such is the nature of hydraulics. Basically don’t worry about it.
