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Pressure
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MattJ
Senior Member


Joined: 19 May 2010
Posts: 35
Location: PNW
Expertise: I live coffee

Espresso: LP-EP Lever
Grinder: Nuovo Simonelli MCF
Posted Sun Oct 13, 2013, 8:10am
Subject: Pressure
 

Recently while doing a little research I read a FAQ about lever machines and the author wrote that a shot should be pulled when the pressure in the boiler is "9 plus or minus 2 bar."  I quickly scampered over to my machine to look at the pressure gauge.  I pull shots at around 1 bar or approximately 14.5 psi.  I remember a discussion on here years ago concerning the altitude of your machine and pressure and a highly regarded member of the community saying that if the pressurestat in a lever was set above about 1.2 bar then most users would over extract their shots.  I then punched in "espresso and pressure" into the googles and was a bit surprised.  Lots of mention of "pressure" with no mention of units of measure.  When units are mentioned they seem to be quoted wrong.  My gauge has both bar and psi (it came from an ag supply store), but I wanted to make sure the conversion is correct so I consulted Al's best invention once again and it seems to be correct at roughly 1 bar being equal to 14.5 psi.  Am I missing something here?

edit - I dug around a little and found the old posts, but they were on a different forum.  I'm not going to post the link out of courtesy, but it wasn't hard to find.  The poster was Stefano out of Eugene who advertises over here too and I misquoted him.  He said he never sets a La Pavoni lever above .9 bar with some people happy with .7 bar.  So, perhaps the FAQ just left the decimal point out of each number, meaning .9 plus or minus .2 bar.  That's the most reasonable thing I've come up with.  Funny that in this little world of home connoiseurs that's exactly the stuff I find maddening.  I can remember very easily grabbing the fragile ring on the pressurestat with needle nose pliers and nervously twisting.  To think you could be doing this and not knowing that you were going for a 10 factor too great :)
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qualin
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qualin
Joined: 30 Jun 2012
Posts: 653
Location: Calgary, AB
Expertise: I love coffee

Espresso: Izzo Alex Duetto 3
Grinder: Mazzer Mini Elect. Type A
Vac Pot: Looking to buy
Drip: Manual
Roaster: Considering?
Posted Mon Oct 14, 2013, 2:31am
Subject: Re: Pressure
 

MattJ Said:

I pull shots at around 1 bar or approximately 14.5 psi.

Posted October 13, 2013 link

I hope not! I pull my shots at 9.5 bar, or about 138.7 PSI! :-)  (Brewing pressure, not boiler pressure.)

Boiler pressure represents the temperature of the shot you are going to pull. The higher the boiler pressure is, the hotter the steam is in the boiler.
For example, Most HX users that I know use 1.1-1.2 bar for their boiler pressure. I know that's pretty much convention.

Now I do know that higher altitudes result in lower boiling temperatures for water, but in a boiler, its enclosed and pressurized, so altitude really doesn't matter. When the gauge
reads 1.2 bar, that boiler is at the same pressure at any altitude. :-)

Just as a FYI, The unit of bar is actually a bit of an antiquated measurement, but the easiest way to remember it is that 1 bar equates to 100 Kilopascals, which is a metric
measurement. It's one of these measurements which was incorporated into the metric system because it is a unit of 10... Even though, we use Pascals instead of Millbars.
As well, I think they use bars because it is easier to fit a "1" instead of "100" on the gauge, or "Bars" instead of "kPa x 100".  :)

Mods: You may wish to move this post to the lever machines forum.

 
Garbage In, Garbage Out, for every step of the process. From Beans to grinder, grounds to machine, coffee to cup.
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NobbyR
Senior Member
NobbyR
Joined: 10 Jul 2011
Posts: 2,041
Location: Germany
Expertise: I love coffee

Espresso: Poccino Opus One, Ariete
Grinder: Eureka Mignon Istantaneo
Vac Pot: N/A
Drip: Melitta Linea Unica de Luxe
Roaster: N/A
Posted Mon Oct 14, 2013, 3:44am
Subject: Re: Pressure
 

MattJ Said:

(...) the pressure in the boiler is "9 plus or minus 2 bar."  (...)

Posted October 13, 2013 link

In an HX or lever machine (steam) boiler pressure is usually 1.1 to 1.4 bar, while brewing pressure should be 9 1 bar.

 
***
"This drink of the Satan is so delicious that it would be a shame to leave it to the infidels." (Pope Clement VIII on coffee, when he was urged to ban the beverage)
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MattJ
Senior Member


Joined: 19 May 2010
Posts: 35
Location: PNW
Expertise: I live coffee

Espresso: LP-EP Lever
Grinder: Nuovo Simonelli MCF
Posted Tue Oct 15, 2013, 11:12am
Subject: Re: Pressure
 

Perhaps we've stumbled onto the confusion.  It appears that .9 bar would be a normal pressure for the EP's boiler while the espresso should be pulled at a pressure of 9 bar plus or minus in the group head including the downward force of the lever.  It seems that bloggers may be confusing these numbers as they are one significant digit from each other.

I don't know how anyone runs a lever with out a pressure gauge.

Note to Mod: like above poster mentioned ^^^ this might go better in the Lever room.  Sorry.
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