mmm mmm good


a wonderful shot (half consumed pre-photo)

I checked brew pressure on the machine and it was higher than I like (10.25BAR)

Chris,

How did you measure Brew pressure? Using a P/F gauge? if so I assume you measured it with no flow. If so, during a shot, the pressure will be different ~ 1 bar lower on a 25 sec 60 oz flow. so the 10.25 bars with no flow, actually translates to ~ 9.25 bars during a shot

I borrowed a trick rig from the Stumptown tech crew that mimics both resistance and flow rate (which I suppose are the same thing you could say) and shows pressure.

You have seen a full BAR difference on the gauge fitted portafilters? In my experience it's been a lot less than that (more like 0.5BAR to at most 0.66BAR).

Hmmm... Actually, let me run over to the roastery and verify those numbers.

malachi wrote:I borrowed a trick rig from the Stumptown tech crew that mimics both resistance and flow rate (which I suppose are the same thing you could say) and shows pressure.

You have seen a full BAR difference on the gauge fitted portafilters? In my experience it's been a lot less than that (more like 0.5BAR to at most 0.66BAR).

Hmmm... Actually, let me run over to the roastery and verify those numbers.

I tested it on Vibe pumps, but not on a rotary. On a vibe it is ~ 1 Bar. That is: 10 bars with no flow will become 9 bars with a flow of 2 oz in 25 seconds.

So that I fully understand, what flow rate did you use when you reduced brew pressure to 9.25 bars?

Just got back.
On the Linea the PF fitted gauge reads almost exactly 0.66BAR high (as compared to both the rig and the in-machine gauge).

Honestly, I don't know what they've got it set to but would have to guess (given the Stumptown parameters) that it is 1.75oz in 27sec.

In order to continue my tweaking for experimentation on this whole clarity/temp/pressure thing, I decided it would be best to turn the Briccoletta (temporarily of course) into a "skeleton" version. I thought you all would dig the photos (grin).

Hey Abe.... to further complicate things I borrowed a different PF fitted gauge from the S-town techies and this one reads a little over 0.8BAR high on the Linea.

D'oh...

malachi wrote:Hey Abe.... to further complicate things I borrowed a different PF fitted gauge from the S-town techies and this one reads a little over 0.8BAR high on the Linea.

D'oh...

Chris,

I found that fluctuations in voltage greatly affect brew pressure at least on a vibe pump. 5 volts fluctuation will produce ~0.3 bar difference. I don't know how it applies to rotary pumps though. On my home Machine I use a variac to reduce voltage from 115 to 100 volts and saw 1 bar difference in brew pressure.

I doubt that would explain it.
I had the two PF gauges side by side on the Linea and saw the same results test after test. I fear at least one of the gauges is inaccurate.