Often-asked Scace 2 question / answer

la marzocco, synesso, simonelli, cimbali etc

Often-asked Scace 2 question / answer

Postby gscace on Wed Oct 08, 2008 7:34 am

Hi:

Here's a question that I received in a PM here that seems worth posting along with the response:

Dan Streetman wrote:Greg,

I am wondering about when using a scace 2 what your experiences have been in the descrepency from the pressure gauge on machines to the scace reading at the scace.

I am asking because recently a customer had a tech adjust their pressure using the scace 2, and he adjusted it to read 9 bars on the device. While I don't believe this is necessarily wrong, I am unsure if this is desirable, or if we should be getting a different reading because of flow restriction etc. They are using a La Marzocco FB-70 Hybrid, with the .08mm gicluers.

Anyway the main reason I am skeptical is that, the coffee has not tasted as good since the adjustment, and a couple of the barista's have commented about the machine making a funny squeaking noise. I also notice that since the adjustment the pump pressure will hit 12 on the gauge, which should activate the excess pressure release into the drip tray, and I am not sure what effect that is having on the extraction.

any thoughts?

much appreciated

Dan Streetman
Cuvee Coffee Roasting Company
Austin, TX


Hi there:

Scace 2 reads pressure immediately downstream of the dispersion screen (or upstream of the coffee cake), as you prolly already know. The pressure immediately upstream of the coffee cake is the most useful pressure value when we are talking about machine setup for specific coffees. All espresso machines experience pressure drop between the pump and the group. Energy gets expended pushing the hot water through tubing, solenoids, and small drilled passageways and the energy used to push the water through the plumbing system shows up as pressure drop. Different designs from different manufacturers use different plumbing schemes, and different designs locate the pressure gauge at different points along the flow path. So if machines A and B are different designs, one can't just adjust the pressure by looking at the machine's internal gauge and assume that the brewing pressure at the top of the coffee cake in machine A will be the same as the pressure at the top of the cake in machine B. The brewing pressure is also affected by group gicleurs and the amount of lime scale present in the system. Small gicleurs and the presence of scale increase pressure drop between the espresso machine's pressure gauge and the group. Any of a range of gicleur sizes may installed in otherwise identical machines (for example, a Linea AV with no gicleurs compared to one with 0.6mm gicleurs), and scale formation may vary considerably from one machine to another, or even from one group to another in multi-group machines. So similar pressures at the internal gauge of presumably identical machines will not necessarily produce identical pressures at the top of the cake.

The whole fluid flow thing has another wrinkle that produces pressure errors - static vs. dynamic pressure. If one measures pressure at the group using a gauge connected to a blind filter, a very common industry practice, the measured pressure will be higher than the actual pressure when brewing coffee. The difference can be quite large. I once was asked to do a technical review of a machine that used a vibe pump with an integrated pressure relief valve. The difference in pressure at the group between static case (measured with a blind filter), and pressure when brewing coffee was 4 bars - HUGE.

So:

1) You should see a pressure discrepancy between Scace 2 and internal pressure gauges because water is flowing through the espresso machine and pressure drop occurs between the upstream internal gauge and the group. The Scace 2 should read less than internal gauges. FWIW, the pressure gauge used in Scace 2 has an accuracy spec of +- 2 psi at normal brewing pressures.

2) Adjusting pressure to 9 bars at the group using Scace 2 may not produce the best result. This is analagous to blindly setting your temperature controller to 203.1 degrees. You must correlate the pressure value to what tastes best. Then use the Scace 2 as a quality control tool so that your machine ( or machines if you are maintaining machines at different locations) produces the same pressure and temperature at the cake as it ages.

3) The pressure value from the Scace 2 is transferable between machines of different design / manufacturer because the indicated pressure is independent of upstream plumbing effects.

Lemme know if you have other questions.

-Greg
gscace
 
Posts: 102
Joined: Fri Aug 12, 2005 7:15 am
Location: Laytonsville MD
full name: Gregory Scace
company: Espresso Research

Re: Often-asked Scace 2 question / answer

Postby Dan Streetman on Wed Oct 08, 2008 11:38 am

Greg,

you read my mind.....


thanks again for the response
Dan Streetman
Dan Streetman
 
Posts: 41
Joined: Thu Mar 06, 2008 5:27 pm
Location: Brooklyn, NY
full name: Dan Streetman
company: Irving Farm Coffee Company
: http://www.irvingfarm.com/

Re: Often-asked Scace 2 question / answer

Postby Ben King on Mon May 18, 2009 3:08 pm

So now that Scace 2's have been out awhile- are people adjusting pumps to read 9 bar at the screen? We noticed a big difference in the delta (Scace to internal gauge) between the GS2 & the Synesso at Billy's shop. FWIW the GS2 has a much smaller delta, which makes sense given the simpler plumbing.

I know the answer is to taste & experiment, but I'm curious what people are finding.
Ben King
Stem Architecture
Portland, Oregon
Ben King
 
Posts: 24
Joined: Sat Jul 28, 2007 6:29 pm
Location: Portland
full name: Ben King
company: Stem Architecture
: http://www.stemarchitecture.com

Re: Often-asked Scace 2 question / answer

Postby nick on Mon May 18, 2009 3:59 pm

There are four relevant pressure measurements:
1) what your machine's gauge reads
2) what your machine's gauge SHOULD read
3) static pressure at the shower head (pressure with something like a blind-filter inserted... most portafilter-pressure-gauges are like this)
4) pressure at the shower head with flow (AFAIK, only the Scace 2 measures this)

The difference (delta) between #1 and #2 has to do with whether or not your gauge is reading properly, but there isn't a very practical way to measure this particular delta. I mention this only because I've seen too many failed gauges. Keep in mind, the gauge reads the pressure at whatever point in the plumbing it reads from. Compare it to peak horsepower ratings for cars, measured at the flywheel.

#3 is sort of like drive-wheel horsepower, measured at the wheels. #4 is sort of like drive-wheel torque, measured at the wheels. Static pressure (#3) tells you the peak pressure that can occur at the head, but pressure-with-flow (#4) gives you a bit more of a real-world scenario. Both more directly relevant than #1 and #2.

All of these are just numbers. As you mentioned, "taste & experiment" will yield the most important info, with the various numbers providing some metrics to help guide your adjustments. As with all measurements, the adage applies: "You don't drink the ____." (fill in the blank with whatever it is you're measuring)
Nick Cho
nick
 
Posts: 1335
Joined: Thu Jun 23, 2005 8:15 pm
Location: San Francisco, Coffeefornia
full name: Nicholas Cho
company: Wrecking Ball Coffee Roasters
: http://nickcho.com
: http://wreckingballcoffee.com/

Re: Often-asked Scace 2 question / answer

Postby Ben King on Mon May 18, 2009 4:44 pm

nick wrote:There are four relevant pressure measurements:
1) what your machine's gauge reads
2) what your machine's gauge SHOULD read
3) static pressure at the shower head (pressure with something like a blind-filter inserted... most portafilter-pressure-gauges are like this)
4) pressure at the shower head with flow (AFAIK, only the Scace 2 measures this)


Yeah, I'm confident that 1 & 2 are close to the same, as we measured the same offset on my Synesso as Billy's. 3 seems pretty unimportant. I'm just curious what people are doing for 4. Now that we have the tools to describe a machine-agnostic spec (#4) it seems valuable to see what others are doing. I'm not proposing that there's a right answer somewhere, but that its interesting.

I've always run my machine at 9 bar as indicated by the machine's gauge & I'm happy with the results, so I'm not changing it just to hit some "magic number." For reference when my machine's gauge says 137 the Scace says 96.

This all stems from needing to get Billy's 2 machines as close as possible in performance for consistency sake.
Ben King
Stem Architecture
Portland, Oregon
Ben King
 
Posts: 24
Joined: Sat Jul 28, 2007 6:29 pm
Location: Portland
full name: Ben King
company: Stem Architecture
: http://www.stemarchitecture.com

Re: Often-asked Scace 2 question / answer

Postby JaanusSavisto on Wed May 20, 2009 12:04 am

Ben King wrote:
nick wrote:
4) pressure at the shower head with flow (AFAIK, only the Scace 2 measures this)


I'm just curious what people are doing for 4.




Our techies built one themselves, just attached a three way fitting to a PF with one way going to gauge and other one going to a tap. When in use one just adjusts the water flow so that an ounce of water comes through to the cup in a normal espresso extraction time. This way it is possible to measure #4.
Attachments
IMAGE_562.jpg
IMAGE_563.jpg
Caffeine. My drug of choice.
Jaanus Savisto
Tallinn, Estonia
JaanusSavisto
 
Posts: 95
Joined: Sat May 27, 2006 9:24 am
Location: Estonia
full name: Jaanus Savisto
company: OY Infomelton

Re: Often-asked Scace 2 question / answer

Postby Klaus on Wed May 20, 2009 3:04 am

Just to answer shortly, I've found that the actual brew pressure for our coffee measured with the Scace 2.0 tastes best at 8,3 bars. Initially I did the same thing when I measured with the Scace - setting it to the "golden" 9 bars in the group, but it didn't produce the best results.

Klaus Thomsen
The Coffee Collective
Blog here
Klaus
 
Posts: 197
Joined: Fri Sep 30, 2005 5:13 am
Location: Copenhagen, Denmark
full name: Klaus Thomsen
company: The Coffee Collective
: http://www.coffeecollective.dk
: http://coffeecollective.blogspot.com


Who is online

Users browsing this forum: Bing [Bot] and 2 guests

cron