New victim for measuring piston pressure: the BOSCO group - Page 6

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JohnB.
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#51: Post by JohnB. »

So the Pro 800 large spring peaks at 7 bar? Is that the highest reading you've seen with the single spring? The real Bosco group uses a 9 bar spring which peaks just over 8 bar. I seem to recall that the Londiniums hit 8 bar also with one spring?

What's the point of having a second gauge facing the opposite direction? Entertaining customers in a cafe?
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dominico
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#52: Post by dominico »

I wonder if there isn't some variation in actual spring tension from group to group. I've tested 3 Faema groups which all theoretically have the same spring, and the peak pressures for the three were 8, 7.5 and 7 respectively. This could be tolerances in the spring or even how (un)successful womeone was at fully screwing in the piston when installing the spring.

Also, Gabor in these videos is lifting the lever rather slowly, this will also have a negative impact on peak pressure. Likely if he lifts the lever up in a much quicker fashion the peak pressure would be a bit higher.
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naked-portafilter (original poster)
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#53: Post by naked-portafilter (original poster) »

JohnB. wrote:So the Pro 800 large spring peaks at 7 bar? Is that the highest reading you've seen with the single spring? The real Bosco group uses a 9 bar spring which peaks just over 8 bar. I seem to recall that the Londiniums hit 8 bar also with one spring?
Somewhere between 7 and 8 bar. We'll see the other groups. Those are simulated pressure measurements. We'll see how it'll be with real coffee in the basket :-).
JohnB. wrote: the point of having a second gauge facing the opposite direction? Entertaining customers in a cafe?
Yes, entertaining customers in a cafe it is extremely important. Coffee will taste better (http://petergiuliano.tumblr.com/post/57 ... -important).

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naked-portafilter (original poster)
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#54: Post by naked-portafilter (original poster) »

dominico wrote:Also, Gabor in these videos is lifting the lever rather slowly, this will also have a negative impact on peak pressure. Likely if he lifts the lever up in a much quicker fashion the peak pressure would be a bit higher.
I like to let go the lever gradually. It seem to be beneficial for the naked pours.

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dominico
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#55: Post by dominico »

naked-portfilter wrote:I like to let go the lever gradually. It seem to be beneficial for the naked pours.
I will also lift the lever slowly on certain coffees, some coffees really respond well to a slower ramp up of pressure.
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pizzaman383
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#56: Post by pizzaman383 »

I just looked at the videos again. I was surprised how the pressure during the shot really doesn't drop very much until all the water leaves the cylinder. It looks like it just drops around 3 bar during the water-flow portion of the shot.

That makes me think that the declining temperature profile of a lever shot probably has more of an impact on taste than the declining pressure.
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aecletec
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#57: Post by aecletec »

pizzaman383 wrote:It looks like it just drops around 3 bar during the water-flow portion of the shot.
Why do you think this isn't a significant amount? I've heard and read from cafe and home users who adjust their machines to 8 or even 7 bar out of preference.
Also, there is this little experiment... http://compoundcoffee.com/experiments/1 ... idamo-Guji

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JohnB.
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#58: Post by JohnB. »

pizzaman383 wrote:I just looked at the videos again. I was surprised how the pressure during the shot really doesn't drop very much until all the water leaves the cylinder. It looks like it just drops around 3 bar during the water-flow portion of the shot.

That makes me think that the declining temperature profile of a lever shot probably has more of an impact on taste than the declining pressure.
A typical single spring version of this group will peak at 8 bar & drop to 6 bar during the shot.
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pizzaman383
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#59: Post by pizzaman383 »

aecletec wrote:Why do you think this isn't a significant amount? I've heard and read from cafe and home users who adjust their machines to 8 or even 7 bar out of preference.
Also, there is this little experiment... http://compoundcoffee.com/experiments/1 ... idamo-Guji
Well, it is a 30% drop in the pressure over approximately 30 seconds so that's dropping .1 bar per second. That is closer to a 1% pressure reduction rate. I was thinking that is a slow rate of pressure reduction.

As those experiments show, lower rates for the whole shot make a significant difference. I wonder what the different rates do to the shot.
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aecletec
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#60: Post by aecletec »

The above is to show a small difference can be substantial. To do the kind of experiment you're considering we might need a user of pressure profiling machine to weigh in. Pressure profiles seem to make a difference on my direct lever but there is the temperature to consider.