Pressure Profiling Techniques for Spring Levers - Page 6

A haven dedicated to manual espresso machine aficionados.
User avatar
JohnB.

Postby JohnB. » Feb 16, 2016, 8:53 am

Dominick - How much flow were you allowing when you measured the 4 bar PI? None? A few drips? Steady flow?
LMWDP 267

User avatar
dominico
Team HB

Postby dominico » replying to JohnB. » Feb 16, 2016, 1:01 pm

Fast drips, not quite steady flow. I did trials with the needle valve at various positions. I am trying to simulate the resistance of the puck during the preinfusion stage.

With the needle valve fully closed I actually had about 6 bar at that position.

I wanted to post a video last night but got side tracked with errands. I will get one posted if not tonight, this week sometime.
http://bit.ly/29dgjDW
Il caffè è un piacere, se non è buono che piacere è?

User avatar
JohnB.

Postby JohnB. » Feb 16, 2016, 3:00 pm

dominico wrote:Fast drips, not quite steady flow. I did trials with the needle valve at various positions. I am trying to simulate the resistance of the puck during the preinfusion stage.

With the needle valve fully closed I actually had about 6 bar at that position.


I just ran some more tests on the Sorrento. Exactly where you hold the lever to pre infuse makes a big difference in the pressure reading. Using steady drips seems to best simulate the levers' normal return speed during a shot.

Holding the lever at the 10:00 position I'm seeing just over 2 bar PI but at the 10:30 position PI jumps to 3 bar. Max pressure seems to be about 7.5 bar during a shot. Bosco uses a 9 bar spring according to Roberta but the normal engagement point is around 10:30 so you don't get the full spring pressure during a shot.

Does your gauge accurately register the boiler pressure when the lever is locked down?
LMWDP 267

bakafish

Postby bakafish » Feb 17, 2016, 2:57 am

I tested with my Rossa PG with IMS basket. After 15 seconds 0 bar preinfusion, opened the air valve to ramp up the extraction pressure to 9 bar within 1 second, it almost choked. With 3 seconds ramp up to 9 bar, the extraction flow rate was normal. I tested the 0 bar preinfusion several months ago, but I forgot how many seconds. I knocked the puck out after preinfusion and found it only wetted the surface.

User avatar
dominico
Team HB

Postby dominico » Feb 19, 2016, 4:59 am

As promised, here is a video of me basically playing around with the pressure gauge and my spring.

I apologize for the ambiance, my machine is in a secret basement location until a kitchen renovation is finished. That could be quite a while.

To understand what's going on better, here's a pic of the face of my gauge:

To note are:
The very first tic is 1 bar. There is no half bar position for some reason. This threw me off at first because I thought the gauge was innacurate measuring my boiler pressure until I realized this idiosyncrasy.
Notice the locations of the 4 and 8 bar positions; they are bolded tics.
Image

Here is some interesting stuff I discovered or verified through these exercises:

The spring maxes out at 8 bar, although it takes very little "help" to get it up to 9 bar or more if desired. (I forgot to film any "pushing" experiments, sorry)

When the lever returns to its vertical resting place, the pressure in the chamber is still rather high, around 7 bar or so. The pressure drops quicker toward the end of the shot. It isn't as linear of a descent as I had imagined. I imagine this would be even less so with real coffee since puch resistance is supposed to drop throughout the shot.

When lifting the lever, the pressure doesn't really start rising until at least the 9:30 position or higher with any air trapped in the chamber.
This means if you want to slowly ramp the lever pressure you should go especially slow toward the end of the lift.

That said, with a controlled lift of the lever it gets easy to "feel" when the lever is slowing down and is going to catch. I have gotten to learn through practice what "4 bar" feels like. This helps me hold the lever at the desired resistance for a higher preinfusion if desired.

http://bit.ly/29dgjDW
Il caffè è un piacere, se non è buono che piacere è?

bakafish

Postby bakafish » Feb 19, 2016, 5:26 am

When you lift the lever, at the beginning, the piston will not move downward until the lever is horizontal. It is the Zodiaco group design. I also DIYed a portafilter with a manometer. It needs some water in it before use. This will banish the air out. If you really banish all the air out, you will find the lever catch point is very low, just above horizontal, and the pressure is 9 bar. But in the real extraction, it is impossible no air in the group, so the catch point is about 45 degree and the pressure is 8 bar. It is because the air volume can be compacted under pressure, unlike the water which is almost cannot be compacted. There should be some compacted air in the group between the piston and water. When the piston stops at the bottom, the air volume recovers gradually and pushes the water above the puck continues going through, so the pressure never drops so fast, but may be faster then the spring pressure profile. If the piston goes to the bottom, without the air, there is not pressure above the water and the pressure drops rapidly.
For reference:
https://vimeo.com/66558244
Please also read the words under the video.

samuellaw178
Team HB

Postby samuellaw178 » Feb 19, 2016, 6:22 pm

Thanks for the video! One thing that stands out to me and needs to be emphasized - every lever group will behave slightly differently, so it's really important to make your own gauge if you want to compare pressure profile.

For my line pressure preinfusion, only a little lift is needed to achieve 4 bar (from 2.7bar). Also, my lever tapers down to about 5 bar (from 8 bar) before quickly declining at the end of travel. By purging all the water and fill the portafilter with water, I'm getting only 8.5 bar. The difference seem much greater on Londinium where Frans has measured 6 bar with air, and 9 bar without air(in the video posted by Ken).

Also, I find it easier to retard/reduce the speed of lever travelling up in order to achieve 4 bar more consistently. If you hold it at an angle, you'll notice (as you did) the pressure is greatly affected by flow rate - unless you grind super fine in which water is not able to flow.

I have tried the stepped preinfusion for a week now. It definitely does something positive to the cup if you're looking for a bit more body/perceived body. Thanks again for starting the discussion!

User avatar
vberch

Postby vberch » Feb 24, 2016, 1:49 am

Great discussion!

User avatar
dominico
Team HB

Postby dominico » Feb 24, 2016, 2:36 am

samuellaw178 wrote:Thanks for the video! One thing that stands out to me and needs to be emphasized - every lever group will behave slightly differently, so it's really important to make your own gauge if you want to compare pressure profile.

Exactly! Today I used my pf pressure gauge on my left group basically as a glorified blind basket to pull a couple shots in succession in order to heat the group quicker, and to my surprise I discovered that this group behaves a bit differently than my right one. Under normal use it only gets up to 7 bar instead of 8 like the right group. (Conveniently enough I primarily the left group for traditional espresso and the right one for SO). I then learned that I can "help" it just a tad to get it up to 8.5 bar.

samuellaw178 wrote:Also, I find it easier to retard/reduce the speed of lever travelling up in order to achieve 4 bar more consistently. If you hold it at an angle, you'll notice (as you did) the pressure is greatly affected by flow rate - unless you grind super fine in which water is not able to flow.


Yes, I've "evolved" my technique to do something very similar. I now lift the lever at a medium pace until I feel the desired resistance and then, rather than stopping, I continue to "creep" the lever up veerry slowly keeping the same resistance until I am ready to fully release it.

samuellaw178 wrote:I have tried the stepped preinfusion for a week now. It definitely does something positive to the cup if you're looking for a bit more body/perceived body. Thanks again for starting the discussion!


No problem! This has been a realy fun discussion so far. I'm glad I threw it together because I've learned a ton based off of others' commentary and techniques as well. And I've been blowing through coffee like mad...
http://bit.ly/29dgjDW
Il caffè è un piacere, se non è buono che piacere è?

User avatar
bidoowee

Postby bidoowee » Jun 11, 2016, 6:16 pm

Hi Dominico,

I read this thread when we discussed it last week but it's taken me a while to get round to writing a reply. I'm curious about where the air in the chamber is coming from. Obviously there is a small amount above the puck and shower screen when the portafilter is locked in (considerably more when using an empty portafilter such as in your setup). When the lever is lowered it creates a negative pressure in the chamber which could draw some air through the puck (or in this case, the valve). The other possible source would be if the water for your group comes from the boiler (which I presume is not the case) and the negative pressure is great enough to draw some air/steam along with the brew water. This seems pretty unlikely, and couldn't happen with a machine that gets brew water directly from the line as opposed to the boiler. So I was wondering what would happen to the "catch point" if you put a check valve in the line somewhere and then pulled two shots in a row. The first shot will guarantee that there is no residual air for the second. You could also just simulate the check valve by closing your valve just before the end of the flow.

Bidoowee