Thank you for this simple and elegant solution. This makes removing the panels and performing pre-infusion adjustments much easier. Also, thank you for your many posts here and elsewhere. I have read many and have always found them to be quite insightful and helpful to my coffee exploration.
Would you please answer a question and help me understand the LR a bit better? Now that I have the pre-infusion module in place, an adjustment up or down will produce changes in extraction temperature, correct? How does a pressure-stat adjustment (the screw under the yellow plastic cap) interact with the pre-infusion module? Why would one change one vs the other?
Thanks for your insights.
we have chosen to regulate the pre-infusion pressure in order to provide a wide range of inlet water temperatures into the brew chamber, rather than regulate the inlet temperature directly because whilst a PID to measure temperature is 'precise' the readings go all over the place whereas pressure is constant, or at least stable, at any given point in the circuit
moving the pressure in the boiler is as good as useless as significant movements in the boiler pressure produce very small movements in temperature in the boiler and elevated boiler pressures will very quickly produce flash boiling in the thermosiphon circuit, which presents as a loss of thermal stability in the group temperature so please never change the boiler pressure from a maximum value of 1.0 bar
when i was using the L3 in the early days i discovered that changing the inlet pressure on the cold water line feeding the L3 had a drastic impact on the taste in the cup. this lightbulb moment was understanding that this was because we had water at very different temperatures in relatively close proximity in different parts of the system; in the core of the heat exchanger the temperature was around 125C yet a short distance away the surface temperature at the group was only 87C
when you increase the pressure in the pre-infusion circuit you are 'blowing' the 'hot' water in the core of the heat exchanger out to the puck much more rapidly and so the group has less time to suck heat out of the water and so it arrives at the puck at a higher temperature (and pressure obviously)
this increase in heat and pressure transforms the thin citrus (lemon, lime) taste of many light roasts into a pleasing sweetness and creates a lot of body
why did we move from a secondary pressure switch to regulate the pre-infusion pressure to a pressure transducer?
primarily reliability: the static pressure present in the system when it is idle is too great for the pressure range that we needed the pressure switches to operate within; the original Ceme was 0-6 bar, the first Mater was 1.5-4.0 bar, and the last Mater we used was 2.0-6.0 bar but the static pressure tends to run around 9 bar and over time it blows all three switches. in comparison the pressure transducer we are using now is rated to operate to 30 bar so it eliminates this issue at a stroke
secondly the pressure transducer allows you to change the pre-infusion pressure by a known amount with no tools required to make the adjustment or to check the post adjustment pressure
for a darker roast you might want a pre-infusion pressure of around 1.0 bar, a medium roast around 2.3 bar, and a super light nordic style lemon juice roast can be transformed into something really remarkable and pleasant with 6.0 bar of pre-infusion
the offset value compensates for the drop in pressure between where the pressure transducer is place and the pressure at the puck and -1.0 bar seems to work well; you can verify this offset yourself with a pressure gauge mounted in a portafilter but please be careful as you need to flush out any air or you will obtain an artificially low pressure reading and it is very easy to spray near boiling water all over yourself
you can adjust the time interval that the pump activates in response to the pressure reading; this helps you to stop the pump chopping in repeatedly in an erratic fashion which is a bit irritating and probably not that great for the pump either
In my view removing the one nipple makes access very easy. The added costs of other alternatives would not be worth it, in my opinion. The Research & Development for the module went directly to the effect of improved versatility in making delicious coffee. The rest would be investing in looks, one of those extras that 10 guys say they want but if it's finished and ready to order most will say "wonderful, so happy I can get it, I might get it sometime next year, maybe" ;-)
Thanks for your thorough reporting, as usual, Frans. After corresponding with Reiss a bit, I decided the timing was right for me and I just placed my order for the digital pre-infusion module for my L-R. I am looking forward to experimenting with different settings as they relate to varying roast profiles. I intend to take advantage of your side panel modification tip for easier access and will also be looking forward to taking advantage of the app once it is developed. Good times. :)
This bad larry right here is giving me some trouble. The spanner-and-hammer treatment worked fine on everything else, but this one refuses to budge. I'm thinking maybe I just need something that can provide more torque, like a socket wrench.