dmau9600 Can’t remember the range on the Bianca, but it’s more than sufficient. In an E61 group there are 3 springs.

  1. Top group valve, pushed open by cam (leave this alone)
  2. Preinfusion chamber valve (opens at 4 bar). The stiffer valve spring is to replace this, to it only opens at 11-12 bar
  3. Vent valve, with spring that opens approx 12 bar

The idea is not not have an operational preinfusion chamber as this interferes with profiling. you can replace the preinfusion spring with the stiffer one and remove the vent spring and valve (or leave it, although the group action might be a bit stiffer). Clives advice is not optimal on this regarding the preinfusion spring..

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      DavecUK

      I hate to be dense, but any easy way you can explain what switching to the stiffer spring would do? I’m not direct plumbed yet.

      Also, should I be less concerned about the flow rate range and just ensure that my flow control config allows me to effectively control pressure at the group head (I understand the pressure control is indirect with flow control, but the end result is real)?

          dmau9600 It effectively stops the preinfusion chamber filling at 4 bar…thus disturbing the profile. The spring doesn’t allow the valve to open until you vent the group.

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              DavecUK so you get more direct and immediate control of the pressure since you’re not accounting for that extra vessel?

                  Still playing and learning with this so bear that in mind.

                  On the Strietman CT2 I’m using an Acaia Lunar 2021 because with some modifications (see https://coffeetime.freeflarum.com/d/956-acaia-lunacy-2021/2 ) to get a handles on flow rate. I’m aiming for 1ml/sec for a dark roast (sometimes medium) 1:1.5 - 1:2.0 ratio. It works well in that context.

                  I’m playing around (without success so far) with light roasts on the Decent and flow rate for that is much higher. I’ll make a note of exactly what it gets up to and update here.

                  Some folks seem to get all concerned that their new, high-fallutin’, shiny spaceship of an espresso machine has had its unburdoned flow rate reduced by the addition of a FCD.
                  Sort of like a guitar amp that goes to 11, “I used to have 30 grams a second!”.

                  For most shots I am using about 60g of water in 30-40 seconds(about a third stays in the puck).
                  So about 2 g/sec average.

                  Unless one is making tea, sorry using barely warmed up green beans to make some sort of Tissane, I can’t see how you would ever need more than around 4-5g/sec.

                    Amberale

                    Thank you! Although a little sassy, I appreciate the insights and feedback. I’ve adjusted the FC to bias towards being fully closed in the closed position, and getting around 5g/s in the open position.

                    With a blank PF, it takes around 10s to reach peak pressure at the group head, but I have much better control of the pressure at the low end now.

                        dmau9600
                        That sounds fine.
                        Once you put about 18g of ground coffee in your basket it should reduce the volume of water required to bring that group head pressure up to your pre-infusion rate (I use 2bar) such that it should take about 5 seconds.

                          2 months later

                          Flow rates always confuse me. On my Bianca with needle fully closed (when paddle to the left), the flow rate is approx 117 grammes over 20 seconds when paddle fully open to the right, which I thought was ok according to Lelit. Is that ok for a flow rate? or does it not really matter as long as the extraction is good?

                            coffeealex the flow rate is approx 117 grammes over 20 seconds when paddle fully open to the right, which I thought was ok according to Lelit. Is that ok for a flow rate? or does it not really matter as long as the extraction is good?

                            117g over 20 seconds is 5.85ml per second, which I think is reasonable for unrestricted flow + as you say, if the coffee is good then you’re all set.