Would like to isolate PM Europiccola group from boiler and, as typical for me, stuck between spending too much or nothing on the project.
With regards to 'too much', found one source of PPS sheet on the web but a 6" by 6" sheet goes for $110.00. Is it really that rare and expensive? Anyone know of any other sources? I was thinking that rigid is more elegant than PTFE with its cold flow property.

Buckley

Another possibility might be polyetherimide (PEI). This is less expensive the PEEK and many other high performance polymers. It is sometimes called ULTEM.

I have always had some doubts about the value of insulating gaskets on La Pavoni machines, especially those with the 1974-2000 groups because the primary way that heat is transferred to the group is from the heat of vaporisation of water brought about by the "steam heated" design that brings live steam into the space above the piston. This forces the top of the group to be at boiler temperature. Furthermore steam condensing against the point where the inlet tube enters the group is also going to be kept at this temperature too. Still, there is a substantial contact area around the group attachment flanges. One can tell that this mode of heating is not all that efficient by touching the group immediately after a machine is warmed up. It will remain practically cool to the touch, but when the group is purged of air so that steam can enter above the piston, it becomes instantly much too hot to touch.

I'd concur with Robert Pavlis on this. I did a study of the pressure-temperature space on the Pavoni, the last run with a 1/16" silicone gasket. Given my interest in reaching a variety of temperatures from 187F to 203F, it would seem that a gasket simply delays the grouphead from getting up to the necessary temperature:

The Relationship Between Water Temperature and Boiler Pressure on a Pre-Millenium La Pavoni

(Also, after a month, very happy with the performance of the silicone gasket. No creep, but as per above, wonder if I should just take it off.)

HTH, Charles

Dear Charles and Robert,
I concur that the condensation of steam above the piston in my PM LP model is the prime agent of heat transfer and the copper down tube attached to the cylinder wall, as well. This why I haven't gone ahead on this mod but I keep re-reading the sighs of satisfaction, including yours, Charles, from owners who have done this.
The rate of heat transfer from the boiler, even off and depressurized, occurs so efficiently that trying to cool the group by putting a cold PF into it, does not significantly affect the group head temperature for more than a few seconds, given the minuscule mass of the PF with respect to the boiler - I do not know under what conditions this would even be worth attempting.
I am currently measuring the boiler and group temps by using a pair of TCs aluminum-taped to the boiler at the level of the downtube intake, not that it matters much, and on the side of the group above the flange, fed into a dual channel readout. I realize that this, too, gives only an approximate idea of brew temperature, but the idea is to use the data to replicate good shots. The trouble is, not having a good shot to replicate because the key to success with the LP is !performance replication!, as so many others have alluded to. Using the LP is like learning a sport, a ski turn or a golf swing, doing it over and over again until the act becomes automatic. The problem is that performance analysts tell us that proficiency begins no sooner than the 300th repetition (for sports, anyway). That is a lot of investment in premium coffee!
Trying to find out what is going on in the brew chamber by what is going on at the surface without performance repetition is difficult because of the offset and lag in temperatures between these two, complicated by the fact that the relationship will depend upon if the temperature in the cylinder is rising or falling and at what rate of change - but this is nothing new to you.
Robert, I have been waiting for you to engineer the hollow tube/TC incursion into the piston but you are likely too proficient to have much need of it while I would benefit from it but do not have the wherewithal to manage it. End of pointless rant.
Buckley

For the record: I find using a thermapen against the grouphead useless because you cannot 'be' with the machine and interrupt your technique to acquire or confirm your datapoint at the same time. One of my hands has to be on the lever while the other is on the base or on the boiler knob or toggling the two switches or getting burnt and I just don't have the time to pick up a second piece of equipment and still have the supposed one degree accuracy that I am shooting for. The same would apply to an IR thermometer, as elegant as that would seem.
B

The thermodynamics of the Pavoni boiler and group are very complex and external manipulations and total ON time have a huge impact on group temperature. Every owner has a specific routine that they have experimentally determined to produce acceptable results for them. Most if not all of these actions are time critical.

Installing a thermal break between the copper boiler and the group will reduce the rate of heat transfer from the boiler to the group but will not stop it, at some point the system will reach thermal equilibrium. The boiler water level will also have an impact on the rate of heat transfer as well and any external manipulations of the piston.

As a result of the heat conductivity characteristics of copper and brass measuring surface temperature and relating that temperature to what is going on inside the group and/or portafilter is only directly relataed to your machine and your routine.

There is another thread on here that actually has some temperature traces taken from inside the portafilter, I do not have a link right at hand but they are highly informative.

IR measurements from shiny objects are highly inaccurate.

The Relationship Between Water Temperature and Boiler Pressure on a Pre-Millenium La Pavoni

This is the link to some temp info.

I have a 1984 La Pavoni Pro, and at one time did have a 1.5mm PTFE thermal break between the group and the boiler. After some testing, non-scientific and not even technical in nature, I found there was little to no difference in the heat of the group. Once I've purged the dry air from the group after it hits full temp in the boiler it gets hot quick and recovers quite quick.

Tried putting in a PTFE air flow restrictor on the back of the group, over the dip tube. It of course didn't do much, because every time you move the lever you bring in new steam to the group. In the end, with the PTFE spreading slightly thinner over time, the experiment was declared a dead end for now.

Group still works well if you just keep a small dish with clean water to pull 1/2 way into the group briefly for a bit of cooling before your shots. RPavlis has documented his shot method of cooling followed by a couple group sprays just before you lock in the PF for the shot somewhere in the forums. It's a good general method for these groups I think.

Best of luck on your experiment!

Old Nuc,
"time critical" and "directly related to your machine and your routine"
I could have saved a lot of typing if I had gotten right to the point, as you did.
DanoM,
Thank you for the reality check. I think most of my effort should be split between my LP technique and finding a Lusso! No mod for now.
Dear Robert,
Thank you for documenting the material choices. I may change my mind.
B

Lusso... Yeah I want one of those too, or a commercial spring lever, or a Strega, or a Pompei... Actually I should be using the word "and" instead of "or" there!

The method you end up using depends on a long list of variables. There is a wealth of information on here and this link is just 1 of many: A Lesson from Christopher Cara in Using a La Pavoni Home Lever Espresso Machine

Once the machine is up to temperature and periodically cycling on the pressure stat the boiler water stratifies and the bottom is cooler than the vapor - liquid interface and the group is being heated by direct conduction and boiler water due to the thermosiphon action. This is when p-stat tuning can help controlling idling temperature.

Once you search out all of the various methods you will be thoroughly confused. Just a few more thoughts this morning.