The effective pressure profile of a specific group/spring correlates strongly with the saturation of the puck / pre-infusion pressure. At higher pre-infusion pressure the engaging point of the lever will be at an earlier (more compressed spring) position.

Lol I knew that that question was coming.

There are two reasons.

Firstly, this is an empirical process. I am starting from an end result: I know , based on much experience, that these machines make superb coffee, and trying to find out exactly what the conditions are that create this.

Secondly, although I know that the generally recommended figure for extraction is 9 or 10 bar, that is for pump machines, which, of course, deliver constant pressure. A higher initial pressure on a pressure profile curve allows water to be pushed through a finer grind. This means more surface area in contact with the water and, I suspect, better extraction/more flavor from less coffee. I don't know about you, but I cannot stand under-extracted coffee.

naked-portafilter wrote:The effective pressure profile of a specific group/spring correlates strongly with the saturation of the puck / pre-infusion pressure. At higher pre-infusion pressure the engaging point of the lever will be at an earlier (more compressed spring) position.

Make sense !
Did you experience lower peaks on your Profitec pro 800 since it's a dipper design?

Happy to see this thread coming up again, can't wait to see the final stage!

cheers

fred

I pulled the second spring out of my Leva a year or two ago. The shots taste the same, I just get to do without the dreaded portafilter explosions off the group. But I find this interesting. I'd love to try a few shots off one of these someday.

Thomas, when will we see pics of the completely assembled machine? Also, when will people be able to buy one? I'll take one with an orange cover please

fredgab wrote:Make sense !
Did you experience lower peaks on your Profitec pro 800 since it's a dipper design?
fred

Now I have a Bosco inner spring with the original outer spring and having a peak pressure at 121C pid setting of 8,5-8,8 bar (espresso weight 43-45g).

arcus wrote:Thomas, when will we see pics of the completely assembled machine? Also, when will people be able to buy one? I'll take one with an orange cover please

Thomas is such a perfectionist that he will only show you pictures of the machine when HE knows it's perfect.
... then you can blindly buy one.

bidoowee wrote: Secondly, although I know that the generally recommended figure for extraction is 9 or 10 bar, that is for pump machines, which, of course, deliver constant pressure. A higher initial pressure on a pressure profile curve allows water to be pushed through a finer grind. This means more surface area in contact with the water and, I suspect, better extraction/more flavor from less coffee. I don't know about you, but I cannot stand under-extracted coffee.

The Bosco & Londinium spring levers produce really nice shots with a peak pressure of 8 bar. My old Strega could hit 11 bar but I much prefer the Bosco's shots.

Nothing like a pressure curve to stimulate discussion (and controversy) around here

@naked - Honored to have your input to the discussion. I completely agree with your statement about the correlation between pre-infusion pressure and 'effective' (as opposed to 'peak') pressure. It is an important distinction to make. The test procedure that I am using does not take the effects of puck saturation into account, as the needle valve is not a perfect analog to the puck.

@John B - Interesting. I've not tried shots from either the Bosco or the Londinium so I can't compare, but again, my goal here is to learn from the masters through emulation and the Aurora is my Las Meninas, Brugnetti('s engineer) my Velázquez. At the same time, I wonder what the end points of the pressure curves are for those machines. What if one were to think about this in terms of pressure over time (i.e. who here remembers their calculus)? What if one were to integrate pressure over time (i.e. calculate the area under the curve) for various pressure profiles. A pump machine running at a constant 9 bar for 20 seconds is 9 bar x 20 seconds = 180 bar-seconds. Because the pressure profile of the spring is (essentially) a straight line, you can calculate the area under that line as a rectangle plus a triangle, or just take the average of the start and end pressures and multiply by the time. So average pressure = (12 bar + 6 bar)/2 = 9 bar x 20 seconds = 180 bar-seconds. Now I'm sure that there is more to it than that, but I do find this back-of-the-napkin calculation interesting.

@fredgab - Trust me, I'm rather keen to see this project to its fruition.

@TomC - Forget about coffee - there is nothing like a good pf explosion to get the heart going first thing in the morning. We'll have to see what we can do about getting you a shot or two .

@arcus - lol orange cover it is! The unveiling and launch will be done when I have confirmed that my new supplier can make the group casting. I placed the order for the castings on January 30th and was told it would take 30 days; hence my rhyme. They started machining the first casting last Monday and I'll talk to the rep again tomorrow to see how far they have got. Once I receive it, it has to be tested mechanically and chemically. Until then, Dr Pootoogoo is right: I don't want to make promises that I don't know I can keep. I am keenly aware that the people who are willing to buy the first machines are going out on a limb and I want to be absolutely sure that they get the best.

bidoowee wrote: @John B - Interesting. I've not tried shots from either the Bosco or the Londinium so I can't compare, but again, my goal here is to learn from the masters through emulation and the Aurora is my Las Meninas, Brugnetti('s engineer) my Velázquez. At the same time, I wonder what the end points of the pressure curves are for those machines.

I'd say that Signor Bosco qualifies as one of those lever masters. My single spring Sorrento peaks at just over 8 bar & drops to around 6 bar as the shot finishes.