Bleeding pressurestat lever machines. (Especially 2nd gen La Pavonis) - Page 4

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OldNuc
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#31: Post by OldNuc »

As it takes hours to obtain actual values relating to heat up from ambient I only have the first set.
Water level at top of glass, system at ambient, 70F. Time to initial P-stat operation with No venting: 8min 54 seconds. Group temp at the top of the lower bell and neck junction ~125F and steadily increasing slowly. After venting the group heats up rapidly as the system heats up to P-stat operation, at that point the group is hot enough to pull the shot.

If starting full have everything ready to go before you have to do the initial vent or you will likely end up seriously over extracted.

Results of a heat up from ambient with the sight glass 1/2 full. Time to initial P-stat operation 7min 3 seconds. Group temperature ~105F slowly increasing. Group temperature at ~9min 110F very slowly increasing

jonr
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#32: Post by jonr »

As Robert suggests, with unknown air/steam mixes, all bets are off wrt heat transfer. Could be better or worse than water.

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drgary
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#33: Post by drgary »

OldNuc wrote:As it takes hours to obtain actual values relating to heat up from ambient I only have the first set.
Water level at top of glass, system at ambient, 70F. Time to initial P-stat operation with No venting: 8min 54 seconds. Group temp at the top of the lower bell and neck junction ~125F and steadily increasing slowly. After venting the group heats up rapidly as the system heats up to P-stat operation, at that point the group is hot enough to pull the shot.

If starting full have everything ready to go before you have to do the initial vent or you will likely end up seriously over extracted.

Results of a heat up from ambient with the sight glass 1/2 full. Time to initial P-stat operation 7min 3 seconds. Group temperature ~105F slowly increasing. Group temperature at ~9min 110F very slowly increasing
Slightly off topic but related to gaining temperature control for shot consistency: I'm very interested to see the comparison of rapid group heating when the boiler is completely versus half full. In my experience with 3rd and 2nd gen machines, group heating even with a full boiler is slowed by a heat break gasket* to prevent quickly overheating. Of course no heat break gasket is possible with the 1st gen group screwed directly into the boiler. 1st gens don't easily overheat for reasons discussed elsewhere.


* Take care to use longer screws to make up for the thickness of the gasket, as Robert pointed out in another thread.
Gary
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OldNuc
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#34: Post by OldNuc »

What happens is the final steady state temp is higher with the high level and the time to too hot is short. A heat break does help but is not going to be a long term solution, just delays the inevitable. The trick is to not vent at all until actually ready to pay attention to the machine.

On another note I have given some thought to the mod that DanoM suggested and think I have an easy way to implement it without all of the machine work that Robert envisioned. It is on the short list.

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drgary
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#35: Post by drgary replying to OldNuc »

It's inevitable perhaps on 2nd gen machines. I can leave my 3rd gen cruising and it won't overheat. The trick there is setting the pressure low enough at about 0.8 bar.

What's the DanoM mod? It isn't in this thread.
Gary
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OldNuc
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#36: Post by OldNuc »

DanoM figured out how to stop/restrict the steam condensing group heating by mostly blocking the port to the top. The Robert mentioned that directly connecting it to the water below the normal low level would stop it completely and require operator action to heat the group. After taking a hard look this looks to be easily doable. This all came up in another thread, "Heat control of 1984 La Pavoni Professional" you commented in this thread as well.

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#37: Post by drgary »

Gary
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EddyQ
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#38: Post by EddyQ »

OldNuc wrote:The practice of releasing water/steam intro the group space before locking in portafilter does not purge all noncondensables from the group but it will changes its internal temperature. Raising the lever to the point just before water release does reduce the amount of air drawn through the puck.
After trying this method to resolve my spongy pulls, I am convinced early release of water/steam is not a good method. Too often, I was not quite as quick with locking my PF and water/grinds blew past the seal into my cup. Not a lot, but enough to upset me. Also, you are right, this technique increases the temperature which I believe may contribute to more water vapor above the coffee. Yes, this vapor collapses instantly with a pull, but it also reduces the shot volume. I plan to raise the level to just before water/steam release and lock in.
OldNuc wrote:Do not ignore the non condensible gasses trapped in the fresh dose of coffee you just locked into the group either. The preinfusion process will purge these noncondensibles into the group. To displace all of those noncondensibles multiple micro pumps, less than a 2-3cm total stroke measured from full up measured at the end of the handle. This works just fine unless the pressure in the group drops below the saturation pressure for the contained water temperature. IF the group piston seals are properly lubed you can both feel and hear the noncondensibles being forced into the boiler. You will also feel the handle contact a very solid resistance to any further down stroke when the group is completely purged.
This method did the trick for me. At first, it failed because I was also experimenting with a lighter tamp and likely stroked slightly more than required. Light tamped pucks do get disturbed very easily at this stage of the pull (as I found out). But with a normal to moderate tamp and very slight strokes, all the air (noncondensibles) exit the entrance hole to the top of the group head. BTW, the entrance hole only falls a very small amount below the seals of the piston. I found this out with a worn level pin issue. In fact, the hole never falls below the piston at all. So, as you say, very slight stroke, preferably never letting the seal go below the hole. And yes, you can feel the lever stiffen.

I also found reducing my dose from 16gms to 14gms might have helped. I think the 16gm doze was against the filter screen. I don't quite understand why that would cause spongy pulls, but if I may fiddle with this more and come up with an explanation.

OK. So now that the air/noncondensibles are in the top of the group head after this pull, what prevents this air from entering again at the next pull? The plastic sleeve in my 2003 has a side channel that goes to the very top of the group. So if there is a bubble of air there, it would be the first to enter (before any water). My thinking is a quick return of the lever to the up position (after first pull) will upset this air and bring it low enough to end up in the boiler with the large swoosh water that resides above the pistol when it was in the down state.

BTW, I do not understand the concerns of heat coming from the boiler to the group via condensing on '84 La Pavonis. My Millenium model has a blocking plug there, so it shouldn't happen with my machine. But I have found that pumping the level, by far, is the fastest way to heat the group too hot and it would be the same for all La Pavonis. Boiler water is cycled through the group with each level motion, regardless if any of the water comes out to the portafilter. So the group heats up really fast with relatively minor leveler pumps and ofcoarse pulling a shot. Perhaps this condensing and conduction type heating is quicker heat transfer than my machine, but it would only make a difference when the machine is idle and at full boiler temperature. Am I missing something? The real issue is removing heat from the group after a level pull so that it is at the correct temperature for the next shot. I've installed an aluminum piece to the sidewall of the group head to mount and monitor temperature with a meat thermometer. If temp is correct (and I am still experimenting what correct is), then I pull the shot. So far, I have not pulled many second shots. But I believe what I will find is a group head that gets too hot after the first pull and needs external means to quickly bring it back (such as wet towel). But I don't understand any modification to the boiler area of these machines making a significant difference.
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DanoM
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#39: Post by DanoM »

EddyQ wrote:But I don't understand any modification to the boiler area of these machines making a significant difference.
I modded my 1984 group with a millenium type group plug, filed a notch in the dipper tube, and turned the group into a water heated group instead of steam heated. In turn I need a digital thermometer, k-probe, for watching the group temperature - not something everyone is interested in doing for sure. With that mod I can run the boiler hotter for better steam, dial in the shot start temperature repeatedly - shot after shot, and cool with only the use of the naked PF locked in the group while I grind and tamp the next shot.

My pulls are very solid, and I don't do any steam flashing or fancy things like that. LIft the lever about 1/2, lock in the PF, raise the lever the rest of the way, count to 10 and I have a solid pull.

Here's the link to the mod: Heat control of 1984 La Pavoni Professional
(In that thread I tried a few different methods, but this is working far better than any of the others. Pulling 8+ shots back to back with the same temp is no problem any longer.)
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OldNuc
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#40: Post by OldNuc »

Operating any La Pavoni with the boiler level at the top of the sight glass or visually at the bottom of the neck to the group will increase the rate of heat transfer by conduction into the group. The net result that for any given time at full pressure/temperature the high level group temperature will be higher than a low level group temperature. The longer the time period the higher the group temperature until the heat loss equals the heat gain.