How I Stopped Worrying and Learned to Love HXs

by HB on Sat Apr 30, 2005 10:03 am

What is all this talk about "flushing" an HX? This how-to introduces the reasons behind the need to flush a heat exchanger espresso machine before starting the extraction and answers practical questions like: How much water do you need to flush? Is it necessary before each extraction or only if the machine has been idle?

Read more...

by **Stadler** on Thu Jul 02, 2009 6:20 pm

Hi,

I have read this article with great interest. However I wonder if there is any difference, regarding group flushing theory, between a plumbed in HX with rotary pump and a HX with tank/vibe. The reason I ask is that I suppose that the water in the thermosyphon can not start to boil in a plumbed rotary machine (due to the pressurized theromsyphon). I have never experienced steam when I do my flushing, only water that is steaming and when I reach the transition point the water is not steaming any more. For a vibe/tank machine the water in the thermosyphon can start to boil due to no waterline pressure in the thermosyphon and as a result of that the heating and flushing of the group might be different? I understand that this is a very theoretical question but it would quite interesting to find out how it works.

by HB on Sat Aug 01, 2009 11:25 am

Sorry for the slow response, I inadvertently overlooked your post.

Stadler wrote:For a vibe/tank machine the water in the thermosyphon can start to boil due to no waterline pressure in the thermosyphon and as a result of that the heating and flushing of the group might be different?

The type of pump has no bearing on the thermosyphon; Eric's diagram from Theory behind flushing an E61 HX machine makes this point clear:

As you see, the thermosyphon loop (red) is isolated from the pump hydraulics (blue) by a check valve and OPV.

by **Stadler** on Sat Aug 01, 2009 5:49 pm

Hi,

Thanks for the response.

I have three comments:

1. I can not find a check valve on my A3. It seems like there is no valve between the pump and the thermosyphon on this machine?
2. I can read the line pressure on the line pressure gauge when the machine is in idle mode. For me, this indicates that the thermosyphon is pressurized in idle mode with the line pressure.
3. The diagram shows a water tank vibe HX machine. I think that there is no check valve on a plumbed in roto HX machine? Is there a similar diagram for a plumbed in roto HX machine?

/Tomas

http://users.rcn.com/erics/ · by **erics** on Sat Aug 01, 2009 6:01 pm

You hereby owe me a beer

This drawing was originally developed by Brad Seaman. If you (or anyone else) would like the original, in pdf format, email me at erics@erols.com

by **Stadler** on Sun Aug 02, 2009 5:42 am

or two...

thanks for the diagram.

/Tomas

by **jmreeves** on Mon Jul 18, 2011 1:20 pm

Firstly thank you for this great article! I was looking for an answer to a cooling flush approach for non E61 Hx aka the pasquini Livia. I am assuming that the approach is the same as the e61s because of similar boiler and reservoir etc. but was hoping someone might either agree or have further insight with non e61 HX. Thanks!

by **frankmoss** on Mon Jul 18, 2011 2:09 pm

I think that the point was that the flushing principle in the same regardless of the type of pump, reservoir, group, etc.

Also, it's good to see another Nashvillian on here. We are few and far between here in the coffee hinterland. In case you haven't heard, Dose just started serving Counter Culture Apollo. And on July 31, a rep from Counter culture is coming to do a cupping that is open to the public.

by **Randy G.** on Mon Jul 18, 2011 3:35 pm

I think the basic theory is that you are trying to stabilize and regulate the brew path's temperature. The pump doesn't matter a bit. What does matter is the design of the machine. The VBM DS (HX machine) requires a different flush volume than the VBM DD (dedicated brew boiler). In general, the DS will require a larger flush volume than other machines because the massive E-61 group holds more thermal energy than other groups. The best thing to learn about the cooling flush is to use Eric's excellent group thermometer (or equivalent depending on the machine I suppose). Having a near-instantaneous display of the temperature of the water going through the group is indispensable when it comes to learning the behavior of any given machine.

by HB on Mon Jul 18, 2011 4:25 pm

jmreeves wrote:I was looking for an answer to a cooling flush approach for non E61 Hx aka the pasquini Livia. I am assuming that the approach is the same as the e61s because of similar boiler and reservoir etc. but was hoping someone might either agree or have further insight with non e61 HX.

As Randy noted, for E61 HX espresso machines, Eric's adapter removes all the guesswork since they are "mixer" types. I elaborated on this point in another thread, excerpted below for your reference:

HB wrote:Having written a number of reviews, I've come to recognize differing degrees of how heat exchanger-centric a particular espresso machine is. My shorthand for these distinctions are:

Dragon - key characteristics are lots of flash boiling, fast recovery, nearly zero thermal memory, and slowly rising brew temperature profile. Simply stated, after the cooling flush, the heat exchanger output is the brew temperature. Examples include the Elektra Semiautomatica, Gaggia Achille, and the Olympia Maximatic.
Mixer - key characteristics are modest flush, medium to slow recovery, considerable thermal memory, and initial rising then falling brew profile. Unlike the Dragon, the Mixer's brew temperature isn't determined solely by the output of the heat exchanger. Other factors, such as cool water mixing via an heat exchanger injector, backflow from a thermosyphon, and the attenuating effect of a heavy grouphead temper the final brew temperature. Examples include HX E61 espresso machines like the Vibiemme Domobar Super and Quickmill Vetrano.
Agnostic - key characteristics are small, fixed volume flush or none at all, and long thermal memory. Careful tuning of a Mixer with tweaks in the design can produce an espresso machine that is heat exchanger in name only. Examples include the Cimbali Junior and Nuova Simonelli Aurelia.
As the last entry suggests, these categories are not immutable. With minor modifications or boiler pressure adjustments coupled with barista techniques, an espresso machine that naturally fits in one category can morph into one of the other categories (e.g, Ian's HX Heaven or 1½ Boiler).

The practical benefit of recognizing the characteristics of heat exchangers is the time saved learning the correct brew temperature management scheme (**). For example, I recognized the Maximatic as a Dragon by flushing the group until the water stopped flash boiling, waiting a minute or so, then repeating; it was fully recovered. The Elektra Semiautomatica is also a Dragon with a slightly heavier grouphead, but they share the same flush-n-go technique for targeting the brew temperature.

In short, for the "Dragon" HX espresso machines, Eric's adapter offers little advantage. For mixers, it's a must have. For agnostics, it's useful only if you're into sub-degree temperature adjustments. The Pasquini Livia 90 is a Dragon, so the flush-n-go technique works best.


Contact Us	Legal disclaimer and copyright: This content and all its parts are copyrighted, all rights reserved. Content including all text and images in part or in whole may not be reproduced in any electronic or printed medium without prior permission. Home-Barista, Home-Barista.com and related logos are trademarks of Home-Barista.com, LLC. Other trademarks are the property of their respective owners. By accessing this site, you agree to the terms of service. Overall speed: , current page: s, avg: s, max: s