E61 thermocouple adaptor and flushing observations - aka backflush cooling flush

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RegulatorJohnson

#1: Post by RegulatorJohnson »

hi.

i have erics TC adaptor in my expobar pulser.

i have been using it and it is great to help learn when the temp is near correct.

i have been flushing lots of water for the cooling flushes before each shot. using a fair amount of water. this lead me to find an external tank for the water, made from a plastic container for holding cereal in a posh way. so now i have my inlet line and the OPV return line in this external tank.

while doing a backflush cleaning with cafiza it hit me what the other line was really for, and what it is really doing. i was getting fresh non soapy water back in the tank while backflushing with detergent. so i was looking at the TC temp while doing this and noting that the brew temp was dropping pretty quickly and also with less water.

i assume because a normal flush the water flows out the group head and down the drain. .. with a "backflush cooling flush" with water from the HX goes through the OPV and back into the tank. the brew temp goes down. you save the water.

i also noticed that if you listen to the output from 3-way valve when you release the pressure that it will "flash boil" and spit and spurt and burp etc when the temp is really hot. after 2-3 10 second backflushes the spitting and boiling goes away. similar to the water dance but out of the 3-way valve, same theory different practice.

anyway.

will my increased backflushing hurt anything? i usually backflush after EVERY shot anyway. this is how i noticed the temps reaction to backflushing related to water usage.

water is cheap. so im not so worried about saving it. i do think that maybe more backflushing cant hurt , i am probably wrong. and if you can clean your machine while you cool the HX then, hey, why not?

thanks for your time.

jon

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HB
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#2: Post by HB »

Interesting observations...
RegulatorJohnson wrote:i assume because a normal flush the water flows out the group head and down the drain. .. with a "backflush cooling flush" with water from the HX goes through the OPV and back into the tank. the brew temp goes down. you save the water.
The HX water shouldn't be backflowing into the tank. Jim provided this diagram:

Image
From How can I adjust the brew pressure of a vibe pump espresso machine?

However, the temperature drop you're seeing could be attributed to water flowing up the return side of the thermosyphon (opposite direction of the blue arrow):

Image
From How I Stopped Worrying and Learned to Love HXs

This mixing is a normal part of the machine's brew operation. On a related note, as I understand it, the Nuova Simonelli Appia / Aurelia Aurelia's use mixing of boiler-heated and fresh water to deliver the brew temperature. Apparently a huge temperature-stable boiler isn't the only way to deliver flat temperature profiles. But I digress...
will my increased backflushing hurt anything?
It's not any more strain on the system than pulling a shot, and I bet you don't worry about "hurting" the machine to do that. ;-)
Dan Kehn

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RegulatorJohnson

#3: Post by RegulatorJohnson »

HB wrote:Interesting observations...


It's not any more strain on the system than pulling a shot, and I bet you don't worry about "hurting" the machine to do that. ;-)
ok i just wanted to ask.. but since you put it like that it makes sense.

so when i then let the water flow without the backflush disc it is at the correct temp.

so can i assume that the HX water is the correct temp but the group is hot. and the cooling flush is cooling the group right? that is why it is called a cooling flush.

HB wrote:However, the temperature drop you're seeing could be attributed to water flowing up the return side of the thermosyphon (opposite direction of the blue arrow):


so this water would probably be cold. at least colder than the HX water. and would this cooler water be a more efficient group cooler than the hot HX water? is this why the group/brew temp seems to drop faster with less water using this method?

so is this water going back up the wrong way after the pressure releases? because it seems like the temp drop happens after i release the pressure then on the next backflush the temp is way lower. it goes down really fast in like 2-3 backflushes depending on the idle time. maybe i can try some more accurate measurements of time and water usage.



jon

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HB
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#4: Post by HB »

RegulatorJohnson wrote:so can i assume that the HX water is the correct temp but the group is hot. and the cooling flush is cooling the group right? that is why it is called a cooling flush.
Correct temp? The HX is immersed in water over 250F... it's going to be very hot in no time flat. The cooling flush is exhausting over-temp water from the HX and warming the group at the same time. It makes sense, especially when you consider how much water it would take to cool an HX surrounded by super-heated water enough such that the exiting water was cool enough to then reduce the temperature of the group / grouphead.

In all the HXs that I've measured, the temperature beneath the dispersion screen is in the 180-195F range. This is shown nicely in E61 Thermal Analysis Questions. I've excerpted my earlier reply below:
HB wrote:Although you hear lots of discussion of "overheated" groupheads, even the hottest ones I've measured idle a couple degrees below brew temperature at the dispersion screen (e.g., 195F), which seems reasonably consistent with your diagram below. That is, I assume your model only takes into account the solid brass, so my delta temperature between the back "red" of the group and at the screen would be a couple degrees more (yours is 197.5-191.8 = delta of 5.7F; mine would be 7-8F, yielding an effective brew temperature of ~202F).

Image
From E61 Group Espresso Machine: Detailed Interior Schematics and isotherm.blogspot.com
Dan Kehn

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RegulatorJohnson

#5: Post by RegulatorJohnson »

so.. what is happening? why does it seems to cool the brew temp?

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HB
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#6: Post by HB »

My assumption is that the pump is pushing the HX water around the thermosyphon loop because there's no exit to the brew group, just the OPV; the exiting HX water has no chance to heat the group / grouphead. In other words, you're cooling only the HX (and not warming the group at the same time), subsequently you use less water. I would expect your overall group temperature to be less stable though.
Dan Kehn

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another_jim
Team HB

#7: Post by another_jim »

When you backflush, once the basket has filled with an ounce or so of water (which is what gets backflushed out), there is no flow at all in the thermosyphon or HX -- there's nowhere for the water to go. The only flow is through the OPV, upstream of the HX.

The cooling you observe is simply the group cooling off. In a thermosyphon, the group heating depends on the thermosyphon circulation, this is cut off during the backflush, so the group is no longer heated. Presumably, in a machine where the group is bolted to the HX and boiler, like the Cimbali, Bezzera, the home Elektra HX, etc etc, backflushing does not affect the groups temperature.

When you finish a flush on a thermosyphon, the circulation is also stopped for a while, and the group cools while the HX water heats. This is how "rebound time" can affect the shot curve. The same effect happens to bolted to the boiler groups, since flushing cools the HX and heats the group away from their idle equilibria. This effect requires a logging recorder, since one needs to study the graphs to see how the curve is affected.
Jim Schulman

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RegulatorJohnson

#8: Post by RegulatorJohnson »

another_jim wrote:When you backflush, once the basket has filled with an ounce or so of water (which is what gets backflushed out), there is no flow at all in the thermosyphon or HX -- there's nowhere for the water to go. The only flow is through the OPV, upstream of the HX.
ok i understand that. makes sense.
The cooling you observe is simply the group cooling off. In a thermosyphon, the group heating depends on the thermosyphon circulation, this is cut off during the backflush, so the group is no longer heated. Presumably, in a machine where the group is bolted to the HX and boiler, like the Cimbali, Bezzera, the home Elektra HX, etc etc, backflushing does not affect the groups temperature.
this makes sense also. i assume the thermosyphon is cut off by the pressure. and the thermosyphon runs still while you have the pump running but not under pressure. and a smaller restrictor in my thermosyphon would keep the group cooler, then less flushing is required because the group is cooler?

i realize that im really cooling the group. maybe this could still be useful after a long idle period? or maybe a couple of backflushes then a cooling flush to even tthe group temp back out. but still u se less water.

could this be useful for those who are putting volvic into the machine and just flushing out 6-7oz a time with the normal "water dance"?

thanks for your help.

jon