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Boiler Pressure in HX Machines: Mini FAQ
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jim_schulman
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jim_schulman
Joined: 19 Dec 2001
Posts: 3,772
Location: Chicago
Expertise: I live coffee
Posted Fri Sep 13, 2002, 3:12pm
Subject: Boiler Pressure in HX Machines: Mini FAQ
 

Ok, you can adjust the boiler pressure on your new HX machine to control brewing temperature. But where to adjust it to?

First off, a few facts.

  1. The guage shows "guage pressure" that is the pressure above the air's. At sea level, a guage reading of 1 bar is 2 bar boiler pressure.

  2. The innards of the boiler are at "saturated steam" temperature for that pressure, that is, the boiling point for that pressure level. At 1 bar, this is 100C, the normal boiling point of water. The table below gives values for espresso boiler pressures.

  3. The Heat exchanger draws water from the mains or tank and runs it through the boiler where it heats up. If the pump isn't running, it heats up to whatever the boiler is at. If the pump is running at espresso making flow rates, it heats up to a lower temperature, hopefully the right one for espresso. There is a sort of design standard out there for espresso machine heat exchangers that most manufacturers follow. The table gives the brewing temperatures implied by that standard.

Here's the table:

Boiler Pressure  Boiler Temp       HX & Espresso Temp
  0.84 bar       117.5C  244F      88C-90C  190F-194F
  1.00 bar       120.0C  248F      90C-92C  194F-198F
  1.17 bar       122.5C  253F      92C-94C  198F-201F
  1.33 bar       125.0C  257F      94C-96C  201F-205F

Remember, even if your machine is designed to this standard, there may be variations. Afaik, this table is roughly right for the E61 tribe, and the Livia. NS plays by it's own rules, so I don't know about the Oscar.

The tradition is to use higher temperatures in this range for lighter roasted bright blends, and lower settings for dark roasted mellow blends. In any case, for a given blend, higher brew temperatures = less brightness, lower temperatures = more brightness. But temperatures outside this range will mess up the extraction, so avoid them.

 
Jim Schulman
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Duncan
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Joined: 19 Dec 2001
Posts: 35
Location: Sydney Australia
Expertise: I like coffee

Espresso: Pavoni, Techno, La Cimbali...
Grinder: Cunill, Rossi RR45, Mazzer...
Vac Pot: No
Drip: No
Roaster: Withams Coffee
Posted Fri Sep 13, 2002, 7:07pm
Subject: Re: Boiler Pressure in HX Machines: Mini FAQ
 

Nice little bit of summary information, thanks.  Can you tell me where some of these defactos standards can be located.  I would be interested to read more about the matter.
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jim_schulman
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jim_schulman
Joined: 19 Dec 2001
Posts: 3,772
Location: Chicago
Expertise: I live coffee
Posted Fri Sep 13, 2002, 7:46pm
Subject: Re: Boiler Pressure in HX Machines: Mini FAQ
 

Duncan Said:

Nice little bit of summary information, thanks.  Can you tell me where some of these defactos standards can be located.  I would be interested to read more about the matter.

Posted September 13, 2002 link

The boiler temperature versus pressure comes from steam tables, my entries are approximate. The equivalent HX temperature comes from a variety of sources, mostly alt.coffee, but also from manufacturers sites that carry machine set-up instruction pages.

But oops! I  stripped the link and metadata from the pages I copied, so I can't give you the web sources. I'll edit the original post adding sources, and make a note of it, as soon as I've tracked them down.

 
Jim Schulman
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