Trapped Air & Spongy Pulls (Again) - Page 2

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John Michael Hauck (original poster)

#11: Post by John Michael Hauck (original poster) »

baldheadracing wrote:I think that we are in agreement.
The one "if" I am wondering about - and will check once I get my machine - is if the three holes that are in the v1 group cylinder are at the same height. ...
I restored a Generation 1 in June of 2020. The three holes are the same height. Sorry. I measured everything to update my CAD models. Still, air might be able to squirm through one or more of the holes once the pressure equalized. Sometimes I imagine that happening when I recklessly jiggle the lever on my Stradivari during pre-infusion.

Enjoy your generation 1!


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baldheadracing
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#12: Post by baldheadracing »

Oh well. I guess if the sponginess really annoys me and/or I wanted a greater water volume, then I could put an anti-vacuum valve on the top of a pressure profiling kit or get the upcoming Bong/Coffee-Sensor kit. It would look weird though - and one of the reasons that I wanted a gen 1 was the cleaner appearance (for example, no boiler mounting flange - and I'm going to remove the group/boiler gauges once the pressurestat and my arm are "calibrated." :lol: )

As the three holes are at the same level, my guess on the purpose of the mysterious well is the same as yours - to hold air. The air in the well should serve to make the piston easier to raise. (I think that it is the highest point in the boiler+group space(?))
John Michael Hauck wrote:... Enjoy your generation 1!
Thanks. I'm really looking forward to getting it. I had always wanted a Europiccola, but it all re-started a few months ago when the Odyssey Argos was announced. I thought that for the same money I could get a nice vintage Europiccola ... and Francesco Ceccarelli had the early B-series that I wanted, complete with all of the Ultimate Europiccola mods done :D.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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drgary
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#13: Post by drgary »

1st gen machines have the same boiler pressure as later ones, because you adjust the steam venting to maintain the boiler pressure the same as if you set the pressurestat for brewing rather than steaming. There's a spring and a ball or a replacement PTFE mushroom backed by a spring. I keep the original steel ball and spring and add tiny shims, measuring boiler pressure through a manometer that I attach to the steam wand.

To the original proposition of this thread, this is just thinking aloud, but I believe the idea is incorrect that flash steam interspersed with air as it initially exits the group is any less dense than drier air. I may be wrong, and if so, please correct me.

What if flash steam expanding as it exits the boiler through the group is more pressurized than air without that flash effect? You would be setting up a pressure wave inside the group that promotes a spongy pull. In other words, expanding steam encounters the resistance of a relatively dry coffee cake. The air before it and the steam that follows aren't exiting as quickly as the pressure is building within the group. This produces the resistant air or vapor pocket.

In the initial thread where Robert Pavlis discusses this issue, he emphasizes the need to pull the lever up slowly to avoid creating a vacuum and a cracked coffee cake. He releases the flash steam and immediately locks in the portafilter. He said it always worked for him. In that thread I proposed a technique of small pumps that infuse the coffee cake for a fuller pull. My thought was to eliminate the fastidious technique Robert was proposing. Here's that thread:

A suspected source of many lever problems: Lock-in

Whether you gently raise the lever and release the flash steam and immediately lock in the portafilter or whether you replace that second step with small pumps after the lever is raised until the puck is saturated, you'll avoid spongy pulls. I agree with Robert's innovation to avoid raising the lever too quickly so that you don't fracture the coffee cake before the pull. This way you will introduce water more slowly and will allow the air or vapor to exit below it without creating a pocket of resistance.

The idea that you seek a hotter group to avoid a spongy pull may prompt people to overheat the coffee. I suggest instead running the boiler pressure relatively low, at about 0.8 bar, and then using half pumps to bring the group up to a desired start temperature to get consistent shots tuned to the roast level of the coffee.
Gary
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What I WOULD do for a good cup of coffee!

John Michael Hauck (original poster)

#14: Post by John Michael Hauck (original poster) »

drgary wrote:... I believe the idea is incorrect that flash steam interspersed with air as it initially exits the group is any less dense than drier air.
Gary, I'm not sure what you are responding to with this sentence. Help!
drgary wrote:...He releases the flash steam and immediately locks in the portafilter. ...
Robert's technique attempts to displace some air before attaching the portafilter, and that makes sense. Note his urgency to replace the portafilter:
rpavlis wrote:I lower the handle just a few millimetres until the steam and water stop, and INSTANTLY put the portafilter in place with my right hand. I put the cup under the portafilter and very quickly raise the handle all the way.
This illuminates Robert's understanding that while the steam displaces the air, the effects don't last long, and air from the environment enters the area. In other words, there is still some air trapped when he attaches the portafilter. What I suspect is really happening is that while Robert's action of releasing steam before attaching the portafilter does indeed displace some air as he claims, it also ensures that the group head and subsequent water will be hotter when he raises the handle all the way. Again, note the urgency of that last action of quickly raising the handle all the way.
drgary wrote:I proposed a technique of small pumps that infuse the coffee cake for a fuller pull.
I believe I understand about infusing the coffee cake (with liquid water) with small pumps. In my mind this is a separate subject. I suppose it is still trying to "get the air out", so I should not be too dismissive. The way I read it, what you proposed and what Robert wrote seem similar:
rpavlis wrote:I pull the handle down just a bit until a few drops of espresso appear, then raise it all the way to the top until the chamber is filled.
drgary wrote:I agree with Robert's innovation to avoid raising the lever too quickly so that you don't fracture the coffee cake before the pull. This way you will introduce water more slowly and will allow the air or vapor to exit below it without creating a pocket of resistance.
I certainly would not argue with that!
drgary wrote:The idea that you seek a hotter group to avoid a spongy pull may prompt people to overheat the coffee.
I agree, and that is why I concluded with this.
The remedy of course is to increase the water temperature by, for example, maintaining a higher group head temperature. However, brewing espresso benefits from water at a temperature in the range of 91-96C to keep it from over-extracting the coffee, which yields a bitter taste. This intricate knife-edged trade-off of these types of lever machines makes them endearing to many.
I really enjoy this exchange. It made me question my understanding even more. For example, your reply got me reading articles about firefighting where they rely on fine-tuning the amount of water being introduced into a structure to maximize the steam generated - to both absorb energy and displace air. One article claimed that this firefighting technique was not widely known until the 1950s.
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jpender

#15: Post by jpender »

drgary wrote:To the original proposition of this thread, this is just thinking aloud, but I believe the idea is incorrect that flash steam interspersed with air as it initially exits the group is any less dense than drier air. I may be wrong, and if so, please correct me.
All else being equal steam is less dense than air. But that's beside the point. The critical difference between air and water vapor is that as air is compressed its pressure increases whereas when water vapor is compressed the pressure stays the same.

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baldheadracing
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#16: Post by baldheadracing »

drgary wrote:1st gen machines have the same boiler pressure as later ones, because you adjust the steam venting to maintain the boiler pressure the same as if you set the pressurestat for brewing rather than steaming. There's a spring and a ball or a replacement PTFE mushroom backed by a spring. I keep the original steel ball and spring and add tiny shims, measuring boiler pressure through a manometer that I attach to the steam wand.
Understood. The current factory pressurestat setting seems to be a compromise in between the pressures folks like for brewing and for steaming. In my gen 1, I had the option of a dual element, but went for a single heating element with pressurestat and a vacuum breaker in place of the ball steam vent. I realize that the original dual control is more flexible, but in my MCaL I always kept forgetting to bleed off false pressure, and so I also wanted a vacuum breaker in the Europiccola. (I retrofitted a vacuum breaker to my MCaL.)
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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drgary
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#17: Post by drgary »

Me: "To the original proposition of this thread, this is just thinking aloud, but I believe the idea is incorrect that flash steam interspersed with air as it initially exits the group is any less dense than drier air. I may be wrong, and if so, please correct me."

John Michael: "Gary, I'm not sure what you are responding to with this sentence. Help!"

I was probably speculating about an underlying assumption that wasn't there. In any case, jpender dispels my incorrect idea.
jpender wrote:All else being equal steam is less dense than air. But that's beside the point. The critical difference between air and water vapor is that as air is compressed its pressure increases whereas when water vapor is compressed the pressure stays the same.
My discussion with Robert in our prior thread was to suggest an easier technique than his that would accomplish releasing an air pocket, and your method seems to be more involved than using the technique I describe. Anyone reading this thread can try the different techniques and see what they like best.

Also to John Michael and Pat (homeburrero): Do you have a link to where Pat was discussing this subject before you initiated this thread?

Too bad that Robert Pavlis and Rich Goodin, aka oldnuc, a technical expert in his own right, are no longer with us to engage in this thread. I miss both of them.

Responding off topic to Craig, who wrote:
baldheadracing wrote:In my gen 1, I had the option of a dual element, but went for a single heating element with pressurestat and a vacuum breaker in place of the ball steam vent. I realize that the original dual control is more flexible, but in my MCaL I always kept forgetting to bleed off false pressure, and so I also wanted a vacuum breaker in the Europiccola. (I retrofitted a vacuum breaker to my MCaL.)
I may adjust my "ultra" Europiccola with a single element and pressurestat to permit constant venting, because I'm unable to set the pressurestat low enough to keep it from overheating. Alternatively, I may change out to a dual heating element and switch to avoid overheating and have higher steam power. In either case the venting would also release an air pocket in the boiler, wouldn't it? But it doesn't release all of the air, which can be trapped in the group. Since you have bought your machine from Francesco, I would love his input on this, if you have a chance to ask him. Perhaps you can message me to have this discussion or I can make sure that the "Ultimate Europiccola" thread is open so we can continue it there. Just let me know your preference with a DM.
Gary
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What I WOULD do for a good cup of coffee!

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baldheadracing
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#18: Post by baldheadracing »

drgary wrote:... Too bad that Robert Pavlis and Rich Goodin, aka oldnuc, a technical expert in his own right, are no longer with us to engage in this thread. I miss both of them.
+10000000000000000000000000000
drgary wrote:I may adjust my "ultra" Europiccola with a single element and pressurestat to permit constant venting, because I'm unable to set the pressurestat low enough to keep it from overheating. Alternatively, I may change out to a dual heating element and switch to avoid overheating and have higher steam power. In either case the venting would also release an air pocket in the boiler, wouldn't it? But it doesn't release all of the air, which can be trapped in the group. Since you have bought your machine from Francesco, I would love his input on this, if you have a chance to ask him.
I'll see how Francesco configured the pressurestat once the machine arrives. I won't be able to use the Scace :), but I've got enough thermocouples and data loggers to get a pretty good idea of performance.

Some thoughts:

In the beginning you are venting air, but that soon becomes steam. The vent is not ideally placed at the top-most point of the boiler, but is probably close enough. There will also be some air in the top of the gen 1 group (unless the machine is first operated upside down to bleed the air from the group), but the guess is that the well in the gen 1 group should hold that air.

In order for there to be constant venting, even with essentially no spring pressure on the ball, the water in the boiler has to be boiling (at least 100C at sea level, etc.). The (gen 1) group design is essentially saturated, albeit restricted by the diameter of the dipper tube. The group's light weight(*) means that it will heat up in stock configuration. To prevent over-heating, the group has to dissipate heat at the same rate that heat is being added. If the heat being added from the boiler at 100C with all else held equal, can the group be modified to radiate that amount of heat? I've seen heat sinks and fans used.

* La Pavoni - about a kilogram. MCaL - a little over two kilograms. Modern lever group - a little over 8 kilograms.

I think that the catch is if one lowers the boiler temperature/pressure to the point that the un-modified group doesn't over-heat over time, then there will not be enough pressure to push water into the group. At the extreme, people holding the boiler temperature equal to group temperature, for example, at 95C, must add a source of pressure to the boiler to push water up the dipper tube into the group.
-"Good quality brings happiness as you use it" - Nobuho Miya, Kamasada

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drgary
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#19: Post by drgary »

Craig,

When you get your 1st gen Europiccola, please start a thread on the topic of whether venting is needed to avoid overheating or whether other measures do the trick. OK, back on topic.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

John Michael Hauck (original poster)

#20: Post by John Michael Hauck (original poster) »

drgary wrote:Also to John Michael and Pat (homeburrero): Do you have a link to where Pat was discussing this subject before you initiated this thread?
Here is one where Robert R. Pavlis and Pat Moore discuss it very crisply:

The Relationship Between Water Temperature and Boiler Pressure on a Pre-Millenium La Pavoni
rpavlis wrote:If too cold the pull will be spongy because the group temperature will be too low for flash vaporisation of water to drive out the air introduced as the handle was pulled up. If too hot your espresso will be over extracted and bitter.
homeburrero wrote:When the first few ml of superheated water enters the brew chamber it will be coming out of the siphon tube at a temp above 212F and will flash boil to steam. This helps drive out the pocket of air that is above the puck right after lifting he lever. (You see discussion of this in the rpavlis post above.) As the pressure builds in the brew chamber, all water above the puck is back to the liquid state, and has been cooled considerably by the brass chamber and portafilter. Ideally to a brew temp in the 195F - 205F neighborhood. The group is cooling the water, and therefore the water is heating the group.