Digital E61 thermometer adapter - Why does group temperature nosedive after flush? - Page 2

Beginner and pro baristas share tips and tricks.
Ken Fox

#11: Post by Ken Fox »

Just for fun, I have temporarily installed a TC into a small, available hole in the grouphead of my 12+ year old Cimbali Junior pourover. This threaded hole is on the top of the grouphead, within the mass of metal that constitutes the brass group which is in continuity with the boiler and the HX in the design of my machine.

The TC is entirely within this small hole, taped over with high temperature tape, and when pulling shots responds more or less instantly to the passage of water through the group.

In my machine at least, as long as the machine has not been at idle for HOURS, the grouphead temp actually goes UP once the boiler water starts to pass through it, and midway through the shot the measured temperature is almost exactly the same as what I get with my Scace device attached to my Fluke datalogger.

When the machine has sat idle for many hours, such as overnight (it is on 24/7) then the measured group head temperature can go up a degree or two, but cooling, if any, is very minimal from what I previously would have called the "cooling flush."


EDIT: see my next post in this thread for a bit of clarification
What, me worry?

Alfred E. Neuman, 1955

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#12: Post by RegulatorJohnson »

that all makes sense.


the technique for this was initially used on a expobar pulser.

i did use this at first to "save" the water in the tank instead of flushing it into the drip tray.

after many shots and observing what was happening with the machine i kept doing it because i liked what what happening from a temperature standpoint as well as not having to fill the tank as often.

... then vetrano came around.

it took some time to get the p-stat set to a point that i could work at a comfortable pace, so the machine would not get ahead of me as far as the temperature. i use the blind "simulated shot" most of the time unless its less than a minute or so between shots. then i will just "check" with a quick ~2 ounce flush to verify im near where i want to be. i use the group idle temp to set my p-stat setting, then deal with the steam as it is or adjust it using the different tips, etc. i like to have the group idle temp be cycling 207-209° i am at 4500 feet so YMMV.

i hope everyone is enjoying some time off for coffee.

2012 BGA SW region rep. Roaster@cognoscenti LA

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#13: Post by RegulatorJohnson »

Ken Fox wrote:but cooling, if any, is very minimal from what I previously would have called the "cooling flush."
is this because your are "cooling" the group with water that is hotter than what it started at?

this is why i like the thermosyphon restrictors because it makes the group a little cooler than where you want it to be.

lets say, id like my group to be 200°-202° because i like that setting for flushing, and a p-stat of .9-1.1 because it works well for the way i steam. with a correct sized restrictor or the variable faema one you could dial an any idle group temp you want. someone else may work faster or slower so this would give them another layer of control over the machine setup.

i could be wrong.


--- raise your hand if your bored, home alone, reading about coffee, drinking whisky, with a foot of snow on the ground.
2012 BGA SW region rep. Roaster@cognoscenti LA

Ken Fox

#14: Post by Ken Fox »

RegulatorJohnson wrote:is this because your are "cooling" the group with water that is hotter than what it started at?
I don't understand your question. My boiler temps are very stable, controlled by a PID, currently set at around 232F. The group head temperature idles around 198-199F at this boiler setting. When the shot starts up, the measured head temp goes up to maybe 202F for a few seconds then starts to decline as the shot progresses and stays around 198-199 for most of the duration of the shot.

In the idling state, the water in the HX should be very close in temperature to the boiler setting, however as the HX water is replaced it is not going to be heated up fast enough to get to the boiler water's temp. Even the initial pulse of HX water comes through the head at a much lower than boiler temperature, and exactly how that happens I don't know. It is either losing heat rapidly along the brew path, or there is a lot of water coming into the HX as the first bit of water is pushed out, so the temperature is reduced that way, by the incoming water from the pourover tank.

So no, in any event, the HX water is starting out at a much higher temperature than the head is idling at, and after a small peak it starts dropping to ultimately below the head's temperature when the shot begun, but only then at the tail end of the shot.

What, me worry?

Alfred E. Neuman, 1955

quar (original poster)

#15: Post by quar (original poster) »

erics wrote:

Data I have shows a 60 second differential in recovery time when the flush to temp is changed by 4 degrees. A gradual lengthening of the recovery time would prompt me to at least do a partial inspection for scale buildup; likewise a substantial reduction in recovery time after a descaling operation would be cause for a minor celebration.

So are you saying for every four degrees, it takes a minute to recover them? In that case, it should take my machine 7 ish minutes to to recover to 212 degrees after flushing to 185, correct? Jon or any other Quickmill owners that might be reading this, could you flush from a long idle down to 185 and tell me how long it takes to recover to 200 deg?


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#16: Post by erics »

So are you saying for every four degrees, it takes a minute to recover them?
Back in February, I ran some flushing tests on Anita as shown below:

The differential between the "180 F" line and the "185 F" was, in actuality 4 degrees vice 5. The recovery time differential to 200 F (in this particular case) was 58 seconds. It is difficult to duplicate these tests because the flushing water temperatures are plummeting fairly rapidly at that point and, stopping the flush at "X" degrees is not an easy task.

In addition to this and AS AN EXAMPLE - say your thermometer is 1 degree off and my thermocouple is 1 degree off; your boiler pressure gage is 0.15 bar off and my boiler pressure gage is 0.15 off. Now, the simple fact is that these numbers are not all that unreasonable and now assume they are in opposing directions.

This is why baseline data on a particular machine (however simple that data may be) and any changes from that data are far more important than the actual numbers.

Eric S.
E-mail: erics at rcn dot com

Ken Fox

#17: Post by Ken Fox »

Thanks to Dan for getting my (fuzzy) images into my post.

Thinking through this further, there is one very important issue about my setup that is NOT going to be typical for a stock Cimbali HX design. The difference, which I've written about extensively before, is that the boilers on my machines are PID temperature controlled at a comparatively LOW boiler temperature and pressure. The 232.5F setting currently on the PID of my Vibe machine, corresponds to a front panel pressure gauge reading of 0.7 bar. I would imagine that most people would have such a machine, in the stock pstat controlled condition, set considerably higher.

I use a smaller flush (50ml) than would probably be used with this machine used intermittently and run off a pstat at a higher setting.

So, in my machines, the flushes tend to heat the group, but in the stock Cimbali setup it may well be the opposite!

p.s. this may also have some bearing on the quality of the microfoam I am able to make with my machines with small quantities (4oz/~120ml) of milk. Using a much higher boiler pressure may require using more milk to get similar results, as the frothing would simply go by too fast with small quantities were the boiler pressure higher.
What, me worry?

Alfred E. Neuman, 1955

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quar (original poster)

#18: Post by quar (original poster) »

Might have found at least part of my problem...Took out the mushroom and the cap nut on top. There wasn't anything but a faint trace of scale, but a ton of chrome flakes had collected in the gicleur screen. Gave everything a good soak in descaler just for good measure and reassembled. Initial GH heatup seems to have taken off much faster. Have to do some testing after it comes fully up to temp, but I'm thinking that the flow through the gicleur was restricted by the chrome flakes. Was rather surprised to see how badly the chrome had flaked off. I'd always taken care to not mix descaler and backflush detergent.

While it was apart, I inspected what I could visually and didn't see any signs of scale buildup. I'd assume that a conventional HX descale routine would handle any moderate buildup in the thermosyphon loop, right?


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#19: Post by HB »

quar wrote:I'd assume that a conventional HX descale routine would handle any moderate buildup in the thermosyphon loop, right?
Dan Kehn