Behaviour inside (older model) londinium group

Terra Banes

I would like to gain a better sense of what is going on behind the scenes, inside the londinium group, as the lever travels through its various positions. Specifically, its impact on preinfusion. Is there a reference drawing I haven’t found which illustrates the water action as it travels inside the group, and how the speed the lever is lowered or raised affects the flow & force of the water impacting the coffee puck?

Frans Goddijn

When you grab the lever and pull, the piston travels upwards. This 'sucks up' air from below the group, through the puck into the space above the puck. Therefore it's important not to tamp too hard because you want a firm puck that will still allow some breathing. Sometimes the puck will momentarily lift up in the filter basket and plop down again, fully intact without any problematic consequences. Then the holes in the basket let the air through, upwards.

Moments later the water inlet holes (see above) are below the piston and at the pressure in the HX, water comes in. The 4 jets neutralize each other and water rainds down evenly on the shower screen from where the water even more gently drips on to the puck.

While you further lower the lever and thereby raise the piston, you push against the spring of the lever, charging it with the power which will be used for the extraction.

With the lever full down, the pressure from the HX pushes water in the group above the puck at HX pressure, against the resistance of the puck which is getting fully soaked and therefore provides a better resistance against the pre-infusion pressure. In the old L1 model, it's very well possible that there is by then an equilibrium between the HX pressure and the puck resistance. Tiny droplets appear below the bottom of the basket but not much is pushed out.

Then you raise the lever and the push of the spring compresses some air above the water column above the puck, then you feel the lever 'grabs' and you can let go since the spring is pushing against the water above the puck and the flow into your cup has started.

After you pull the cup, some more water is pushed out, and if you let the machine alone for a bit while sipping your espresso, the compressed air above the water is pushing the last of the water out the puck and also some of the air and that's how you end up with an almost 'dry' puck, as opposed to E61 type machines which will mostly have a wet muddy puck.

Terra Banes

Thank you, Frans, for the details & pictures. Most helpful!

I have had a sense that I get better flavour if I very slowly lower lever at the point where water is beginning to be released, than if I simply bring the lever down at a more normal speed. If I understand correctly, this is allowing water to impact the puck much more gently. Is that indeed the case (on the old londinium 1)?

I assume I am also allowing more water to enter into the group itself, when I pull more slowly (& release more slowly at the catch point), but perhaps not?

ps
Are the 4 water inlets really as tiny as they appear? Wow! And opposing jets! Who knew?! Prior to seeing your pix, I had erroneously assumed there was one large inlet hole that water passed through & gushed into the group full force!

Frans Goddijn

Terra Banes post=16284 wrote:
I have had a sense that I get better flavour if I very slowly lower lever

Pulling the lever gently, not agressively is okay, but I don't think pulling it VERY slow is especially helpful. The design of the group and piston is already done to generate a gentle rain of water. Keepin the piston at the point where the inlet holes are almost or hardly opened could potentially work like squeezing the end of a garden hose, with a more agressive spray.

Terra Banes post=16284 wrote:
I assume I am also allowing more water to enter into the group itself, when I pull more slowly (& release more slowly at the catch point), but perhaps not?

Having the lever down longer allows more water to soak the puck, but beyond the "droplets below the basket" point not much happens beside everything cooling down.

Terra Banes

Ah-ha! The garden hose analogy is a very good one!
Your info has given me a much better sense of the water flow, so now I will be better equipped as I experiment some more.:)
Thank you!

Terra Banes

Frans, You are 100% correct in your “garden hose” suspicion. I took the shower screen off the group just now for cleaning, and while doing this I remembered your comment about the effect of slowly pulling down on the lever. So, I watched the water as it exited with the screen removed. With a slow pull, there are 1 or 2 pinhole sprays from each side, nothing in the middle & main area of the grouphead, nothing to gently & evenly hit the puck. The few pinhole sprays would hit the side edges of the coffee puck and not much more; whereas, with a full-on pull down, the water appears to more gently & somewhat evenly spread out & over the puck area. Interesting stuff to observe!

Frans Goddijn

Happy to hear this!

Paweł Walczak

Great explanations Frans, as always.
Can you please provide the same level of details for LR?

Reiss Gunson

there is no difference in the group for the LR to any of the others

the only difference in the L1/2/3 & LR over the L1(2012-16) is the ability to vary the pre-infusion pressure, and changing this variable also changes the brew temperature and the brew volume

kind regards

reiss.