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Permalink Reply by Brady on July 9, 2012 at 5:24pm

Dylan, your machine is set correctly. Your understanding is also correct, just a little incomplete.

Your espresso machine actually uses two very different sets of temperatures and pressures because it needs to do two different things - extract espresso and steam milk. Espresso extraction ideally uses 200ish degree water at a pressure of 9ish bar (that's fluid water pressure). Steaming milk ideally involves 1-1.5 bars of steam pressure, which requires the water to be significantly above its usual boiling temperature (in the 220+ neighborhood). For this reason, it is important to understand which temperature and pressure you are looking at.

The way the Adonis and other heat exchange style espresso machines make this work is by using separate chambers inside the boiler to isolate the brew water from the steam+water mixture. This is different from the way multiple-boiler machines (like La Marzocco) which use separate boilers for steam and water. This enables the brew water to be at a much lower temperature and higher pressure than the boiler water.

Many espresso machines have gages to indicate steam pressure and water pressure. Machines with digital temperature control may also indicate brew water and/or boiler water temperature. If brew water temperature is not displayed, a thermometer (ideally a Scace device) must be used to measure it.

Your machine settings sound about right.

Hope that helps. Let me know if any of that needs additional clarification.

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Permalink Reply by Brady on July 9, 2012 at 5:45pm

Oops. What I meant to say was "Both approaches enable the brew water to be at a lower temperature and higher pressure than the steam boiler water". Apologies for any confusion.

Brady said:

...The way the Adonis and other heat exchange style espresso machines make this work is by using separate chambers inside the boiler to isolate the brew water from the steam+water mixture. This is different from the way multiple-boiler machines (like La Marzocco) which use separate boilers for steam and water. This enables the brew water to be at a much lower temperature and higher pressure than the boiler water.

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Permalink Reply by Dylan Henson on July 9, 2012 at 10:30pm

Thanks, Brady! I'll have to read up on the heat exchange mechanics to understand the exact reasons, but you cleared it up perfectly.

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Permalink Reply by Brady on July 10, 2012 at 4:01am

Here's a link to the Aurelia's hydraulic diagram - iirc the pump-driven Arduinos use the same setup.

The heat exchanger is the tube running diagonally in from the bottom of the boiler and out the top. Note that cold water is injected into the middle of the chamber to mix things up. There is also a return loop running back from the group so that the hot water can circulate at idle through natural convection. This thermosiphon effect simultaneously heats the brew group and cools the brew water, keeping them both at or near the ideal 200ish brew temperature. This is despite the fact that the water surrounding (or mostly surrounding, the steam boiler is only 2/3 full) the heat exchanger is running over 220F.

Lots more out there if you are interested. Good luck.

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