The Impact of Autofill on Shot Temperature and Pressure in an HX Machine - Page 2

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Ken Fox (original poster)

#11: Post by Ken Fox (original poster) »

RapidCoffee wrote:This topic was discussed a few months ago on the How Autofill Degrades Shot Temperature Stability thread. On my rotary pump Vetrano, autofill clearly reduces group head pressure. I don't think it really matters whether the pump is vibe or rotary; when you open an alternate water path to the boiler, pressure is gonna drop at the brew head. My question is, what wizardry does Cimbali use to avoid this?
________
John
Hi John,

I have been giving this matter some additional thought.

The other thread wasn't really so much about autofill occurring INTRA-shot as it was about autofill occurring during a session when many shots (with frothing) are made. The autofill would have been triggered in the earlier test scenario by doing a lot of frothing, however each simulated frothing session would obviously expel less water than what would be needed to trigger the autofill. In the current series I abruptly removed 100ml of water from the boiler in several seconds, which obviously would trigger the autofill.

I should add also that it is a bit difficult in a typical machine to be absolutely certain that the autofill is filling the boiler at the same time as the shot is being made. The obvious reason is that the rotary pump and motor are going to be running to make the shot, and in the absence of a sight glass one is looking for additional noises like maybe something coming out of the input solenoid to try to confirm that the boiler is being filled at the same time. Since autofill machines aren't made (or at least aren't made anymore) with sightglasses, you have no visual cues to guide you either.

It is certainly possible that changes in sounds that I heard after the 100ml of water was removed from the boiler could have been something other than the boiler filling and since the rotary pump remained on after the shot was completed it is definitely possible that no actual boiler filling occurred during the shot even though the autofill circuit was indicating a need for a refill. If so, then both test scenarios, as reported in this thread and the other one, were actually similar with the major difference being the volume of fresh water put into the boiler by the autofill during the test series. The earlier series probably introduced a lot less water as the simulated frothing sessions would have almost certainly expelled less than 100ml of liquid water equivalent.

As to how Cimbali would have managed to refill the boiler simultaneously as the shot was being made, without effecting the shot pressure, I guess the first question would be whether the boiler is actually refilling intra shot even though the boiler circuit is calling for it. Possibly, with a trained ear and multiple tests, after taking the side panel off and listening with your ear close to the boiler it would become obvious. Perhaps Michael Teahan or TJ or someone else who really understands how these things work can explain it since I'm not sure of a good way to convince myself whether the boiler is actually refilling intrashot or not. IF the boiler is actually refilling intrashot, then there must obviously be enough power in the pump and motor to accomplish both tasks simultaneously, or the plumbing must be set up in a way to preferentially give the pressure to the shotmaking circuit in favor to the boiler refilling circuit.

ken
What, me worry?

Alfred E. Neuman, 1955

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HB
Admin

#12: Post by HB »

RapidCoffee wrote:On my rotary pump Vetrano, autofill clearly reduces group head pressure. I don't think it really matters whether the pump is vibe or rotary; when you open an alternate water path to the boiler, pressure is gonna drop at the brew head. My question is, what wizardry does Cimbali use to avoid this?
Ken Fox wrote:IF the boiler is actually refilling intrashot, then there must obviously be enough power in the pump and motor to accomplish both tasks simultaneously, or the plumbing must be set up in a way to preferentially give the pressure to the shotmaking circuit in favor to the boiler refilling circuit.
I haven't given this serious thought since an inopportune auto-fill during an extraction is a very rare event. Maybe once or twice in the last few years? I don't know the inner plumbing details of your Cimbali Junior, but a restrictor (orifice) for the boiler refill leg of the circuit similar to the grouphead gicleur would impede the inflow enough such that the pump pressure would remain steady. It shouldn't strain given that it can put out 900cc/min at 8 bar.
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Ken Fox (original poster)

#13: Post by Ken Fox (original poster) » replying to HB »

I agree and think that an inopportunely timed extraction would be mostly an issue when one tried to bang out shots for a large number of people many or most of whom requested milk drinks. Then, I think you would get what I demonstrated in the earlier thread with a wider degree of shot temperature variation than one would get normally. Of course, my system has its temperature controlled by a PID and I have the boiler temp set lower than most people would use it for repetitive shot series with mostly milk drinks, so quite probably in a stock system this all would get lost in the "background noise" of a pstat driven system operating at a higher boiler temperature, albeit with more temperature variation than I normally see in my system.

As an aside from the earlier thread, I had given serious consideration to modifying my machine, yet again, to try to prevent inopportune boiler fills, using a relay and perhaps other electronic parts. After a little bit of reflection I decided not to bother with it as in my actual usage pattern large runs of drinks, especially large runs of milk drinks, happen seldom or never. Having now done this second "experiment," where at least 100ml of cold tap water were quickly dumped into the boiler during a shot series, and seeing how little difference it made in the shot temps obtained, I'm even more inclined to leave well enough alone.

For those with upcoming parties where they anticipate pulling long runs of milk drinks, it would not be a bad idea to prepare in advance by bleeding off enough water from the boiler to turn on the autofill. At least that way you will know you are starting out with the boiler at the high end of its fill range, and you will reduce the likelihood of an inopportune autofill cycle. It would not be a bad idea at all to bleed off a few ounces of water every couple of days in regular domestic use, which will have the benefits of both reducing the likelihood of scale buildup, and of reducing inopportune boiler fills during your normal espressomaking routine.

ken
What, me worry?

Alfred E. Neuman, 1955

User avatar
jesawdy

#14: Post by jesawdy »

Ken Fox wrote: As to how Cimbali would have managed to refill the boiler simultaneously as the shot was being made, without effecting the shot pressure, I guess the first question would be whether the boiler is actually refilling intra shot even though the boiler circuit is calling for it. Possibly, with a trained ear and multiple tests, after taking the side panel off and listening with your ear close to the boiler it would become obvious. Perhaps Michael Teahan or TJ or someone else who really understands how these things work can explain it since I'm not sure of a good way to convince myself whether the boiler is actually refilling intrashot or not. IF the boiler is actually refilling intrashot, then there must obviously be enough power in the pump and motor to accomplish both tasks simultaneously, or the plumbing must be set up in a way to preferentially give the pressure to the shotmaking circuit in favor to the boiler refilling circuit.
Ken et al.

Finally got a chance to read this thread.... and I looked at the plumbing diagram and electrical diagram for the M32 Bistro (which is not the M21 Junior, but hey, it is Cimbali). I am not an expert in reading said diagrams, but I believe on the M32 at least, it is electrically wired such that the Coffee solenoid and the Boiler supply solenoid cannot be active simultaneously. My suspicion is that the level sensor is detecting low level, LED indicates that boiler refill is needed, but not necessarily occuring. The wiring diagram indicates that pump motor relay is tied to the coffee solenoid and the boiler supply solenoid, but there is a switch that limits it to one or the other.

Ken, if you are so inclined, you could put a meter on the boiler supply solenoid, and see if it is actually opening intrashot or not when a refill occurs. I think it is actually opening immediately upon completion of the shot when the boiler level sensor is calling for refill.

I can attempt to post the electrical diagrams if you'd like.

The hydraulic diagram also shows an "Injector" on both the Coffee plumbing circuit ahead of the heat exchanger, and on the boiler supply plumbing ahead of the Boiler supply solenoid valve. There is a third "Injector" ahead of the water supply tank solenoid valve as well (The M32 1-group has a pour over type reservoir, even though it can be direct plumbed). I am not sure what is meant by an "injector", but based on the three locataions, I wonder if they are some sort of flow restrictor or orifice. Is this consistent with a gicleur (I'm too lazy to look right now)?

UPDATE - For this one, it is simpler to link to a PDF of the diagrams that I created. Get a copy of the electrical and plumbing diagram here.

-Jeff
Jeff Sawdy

LeoZ

#15: Post by LeoZ »

while we seem to be drifting onto the subject.. is there any benefit to upgrading my pump from vibratory to rotary? would it impact the machine internals in any negative way?

Ken Fox (original poster)

#16: Post by Ken Fox (original poster) » replying to LeoZ »

Based upon blind taste testing done TWICE over ~2 years by Jim Schulman and myself, I/we would say that if your goal is to make better shots, you would be wasting your time doing a rotary conversion as there is no evidence that a properly set up vibe machine makes less tasty shots than a rotary machine. I am assuming that you have an overpressure valve and it is set to some sort of reasonable value such as 9 bar. In fact, if your machine lacks preinfusion, the slower pressure ramp up of a vibe pump is much more forgiving for shotmaking than is the almost immediate ramp up with a rotary, in a sense making a vibe machine superior for all but the very best baristas who may not need "forgiveness" in their machines.

Rotary pumps are quieter, of course, so one might desire to have a rotary pump driven machine for reasons other than shot quality. Converting a machine from vibe to rotary is not a simple matter of swapping out the vibe pump and replacing it with a rotary pump and motor, however. A long time ago I considered doing a rotary conversion on my old vibe Cimbali Junior and later, with the testing we did, I decided that this was not worth doing, at least for me.

ken
What, me worry?

Alfred E. Neuman, 1955

Ken Fox (original poster)

#17: Post by Ken Fox (original poster) »

jesawdy wrote:Ken et al.

Finally got a chance to read this thread.... and I looked at the plumbing diagram and electrical diagram for the M32 Bistro (which is not the M21 Junior, but hey, it is Cimbali). I am not an expert in reading said diagrams, but I believe on the M32 at least, it is electrically wired such that the Coffee solenoid and the Boiler supply solenoid cannot be active simultaneously. My suspicion is that the level sensor is detecting low level, LED indicates that boiler refill is needed, but not necessarily occuring. The wiring diagram indicates that pump motor relay is tied to the coffee solenoid and the boiler supply solenoid, but there is a switch that limits it to one or the other.

Ken, if you are so inclined, you could put a meter on the boiler supply solenoid, and see if it is actually opening intrashot or not when a refill occurs. I think it is actually opening immediately upon completion of the shot when the boiler level sensor is calling for refill.

I can attempt to post the electrical diagrams if you'd like.

The hydraulic diagram also shows an "Injector" on both the Coffee plumbing circuit ahead of the heat exchanger, and on the boiler supply plumbing ahead of the Boiler supply solenoid valve. There is a third "Injector" ahead of the water supply tank solenoid valve as well (The M32 1-group has a pour over type reservoir, even though it can be direct plumbed). I am not sure what is meant by an "injector", but based on the three locataions, I wonder if they are some sort of flow restrictor or orifice. Is this consistent with a gicleur (I'm too lazy to look right now)?

UPDATE - For this one, it is simpler to link to a PDF of the diagrams that I created. Get a copy of the electrical and plumbing diagram here.

-Jeff
What I'm curious about is whether the input solenoid will even permit the water to go in two directions simultaneously, e.g. to the boiler AND to the group. If this is not possible than the question answers itself as the water can only go one place at a time and not two, which would mean that no matter what the autofill circuit is calling for, if it is subordinated in the solenoid, what it wants and what it gets are two different things :P The situation might be different with double boiler machine, so this comment is directed only at HX machines.

Unfortunately I cannot test anything right now as I am in France and will not return home for almost a month.

ken
What, me worry?

Alfred E. Neuman, 1955

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TroyR

#18: Post by TroyR »

Topic merged to prior thread by Moderator

Other than the obvious of course, which would be pumping reservoir temperature water into the boiler probably lowers boiler temp.

So temperature is managed via pressurestat in my Hx boiler, what effect does pumping additional fluid volume into the closed system have?
Will temperature actually rise via a magic water-pressure relationship? Or will my temperature fall due to the fact that the pressure was increased by adding fluid volume instead of adding more heat?
Whichever way it happens, is a temperature rise or fall compounded by or negated by the addition of reservoir temp water entering the boiler?

Man, I hope that made sense.

BTW, I have a Bezzera BZ02.

Cheers,
Troy

Ken Fox (original poster)

#19: Post by Ken Fox (original poster) » replying to TroyR »

Thanks for resuscitating this long dead thread that deserved to have died a long time ago :roll:

I do not understand your question, to be honest. If the question involves what happens when you pull a shot and water is introduced, that water is of course in the heat exchanger circuit and merely passes through the heat exchanger which is located in the boiler, but has no impact on boiler pressure other than to slightly lower it since cooler water entering the HX will have some impact on boiler temp.

If the question concerns autofill or manual boiler fill, hence increasing the volume of water in the boiler, then what is happening is that cooler water is introduced into the boiler which of course increases the amount of water vs. air/gas/steam space in the boiler, but reduces the pressure because it cools off the system. Later, a few seconds later, after the pstat has called upon the element to heat up the water, the element will then be turned off when the pstat cycles off because the pressure is back at the top of the range, hence there is essentially no change.

If on the other hand you were to introduce very hot water into the boiler, that might have other effects such as increasing the boiler pressure but the pstat would be off at that point and would wait for the temperature to fall before calling upon the element to fire on again. Of course that is not going to happen as the water inflow does not come from pressurized heated water but rather from room temperature or even cooler, water.

Hope this makes sense.

ken
What, me worry?

Alfred E. Neuman, 1955

TroyR

#20: Post by TroyR »

If the question concerns autofill or manual boiler fill, hence increasing the volume of water in the boiler, then what is happening is that cooler water is introduced into the boiler which of course increases the amount of water vs. air/gas/steam space in the boiler, but reduces the pressure because it cools off the system. Later, a few seconds later, after the pstat has called upon the element to heat up the water, the element will then be turned off when the pstat cycles off because the pressure is back at the top of the range, hence there is essentially no change.


Thanks Ken, this is the scenario I was thinking of.
When the machine autofills and pumps water into the boiler wouldn't there be a pressure increase due to the fact that it is pumping into a closed system? This alone should de-activate the heater.
However, as you mentioned, if the addition of cool water should cause the pressure to drop then would you expect that these two occurences effectively negate each other?
IF they did in fact negate each other, then couldn't we be left in a situation where our heater is off because the pump bumped up boiler pressure even though our boiler temperature has been lowered by the addition of fresh water?

How differently would you expect the machines you tested and datalogged to behave if they were controlled by pressurestat as opposed to PID?

Troy