OldNuc wrote:Well not quite the same, that is probably the issue. I suspect the tying the 2 areas together is not going to catch it for most users. To be honest I am not having an insurmountable issue with the machine as built but I realize for what you are doing it is completely inadequate. As I have not spent much time thinking through the thermal hydraulics of this mod I have not started making parts to test out the idea as there are several approaches and they will have short term and long term results that will be different. I do not pull 8 shots in rapid succession and usually only pull 2 double shots back to back with a delay before the next round, then the machine should idle for at least 3 hours and not end up overheated. That is initiating the process with sight glass cold level at the very top of the glass.

For me, it works fine for one or two shots, but if I want to compare grinders, or take it to a friends house and test a few different coffees its totally inadequacy. Worse is if something happens during preheat-like have to help my daughters with something--and then I have to cool the group. Would really love to see this work out well!

Of course, it worked fine in stock configuration for me with 2, maybe 3 shots also. After that I had to cool the group for the next shot. Not many people are going to use this machine for 8 shots every morning. I'd rather be using the Strega & K10 for that too instead of the La Pavoni and my kludge grinder.

This mod is probably not a requirement or serious concern for 95% of the La Pavoni users out there. But if you're frequently hitting high temps... it's something to consider. I like it better than the ramekin cooling when I hit that point, and I use less water in flushing this way. The drain tray suffices for all 8 shots without the need to dump it, but that might just be my issue.

You have put your finger on the issue I suspect to still be a problem with both volumes tied together. If machine sits and idles with sight glass at full it will probably end up way overheated and no easy way to cool it off. I never flush the machine as you are dealing with a 2 phase flow through an orifice along with adiabatic expansion. This becomes instantly complex and a mess. Generally that mix of liquid and vapor is going to be right close to 100C.

If it wasn't so hot here today I'd fire up the machine with and without the mods to get some temp readings over a period of several minutes. Maybe someday in the near future when it cools down a bit.

With the boiler set for 1Bar I should have an average temp of about 120c in the boiler itself, and in my experience that will overheat the group very quickly without any mods in place. We'll see though, as without any actual data readings written down this is mere speculation on my behalf.

You are correct, 1 BAR, full glass and it will be way too hot in under 15 minutes once noncondensibles are vented off. The time to way too hot increases exponentially as the level drops so at 1/2 glass you have a fair amount of time before it has overheated.

Worst case condition is with the full sight glass. With a lower level of 1/2 full sight glass your mod may never overheat.

DanoM wrote:This mod is probably not a requirement or serious concern for 95% of the La Pavoni users out there. But if you're frequently hitting high temps... it's something to consider. I like it better than the ramekin cooling when I hit that point, and I use less water in flushing this way. The drain tray suffices for all 8 shots without the need to dump it, but that might just be my issue.

Thank you both for explaining this mod so well. There is another group of users who would benefit. Many beginners want a good but inexpensive starter machine, get a 2nd gen La Pavoni and are unable to control it because of its tendency to overheat. If a simple part stabilizes that you've created a low cost, high quality option for them.

I think either approach that has been discussed here will terminate the tendency of the 2nd gen la Pavoni to go super nova in a matter of minutes.

I've really been appreciating the wealth of information from, especially, this thread.

I do just fine with my normal flat white in the morning, flat white in the afternoon, but if I take my machine over to my folks, I fight the overheating problem when trying to make multiple drinks. I do all the common cooling methods: toggling power, cold towel, cold portafilter, etc., but it's hard to stay on top of it.

Thanks for helping me understand the difference between the generations and the relationship to the steam inlet on mine causing the high temps.

I still haven't updated this topic properly, but thought I'd add a few notes on my hot water heated group.

After running vinton o-ring seals on my group plug for about 3-4 months I needed to replace them. There wasn't enough spring left in them to keep the plug from sliding back out until it was hot. Still it's a cheap replacement part for a stable group.
I'm pulling around 250 shots per month on this at 8 per morning, back to back. A water cooled naked PF is all I need to accomplish cooling adjustments.

Typically I get the boiler heated up to 1-1.1 BAR, giving me good steam for cappuccino. Then pump the lever, wait a couple of seconds, pump the lever, repeat until I hit about 94c on my digital thermometer. Each pump will raise the temp of the group around 5c early on, and then about 2c+ towards the end.
Once I hit at least 94c I slap in the naked PF, cooled in cold tap water, and bring the group temp down to 91.5-92.5c depending on the coffee I'm pulling. This can happen while I grind and tamp into the basket.
Fine tuning the start temp is as simple as moving the lever a tiny amount, and I'm able to raise it 0.2c at a time with ease.

The lever is no harder to move than when the group was steam heated, so that's good. Not yet sure if there is extra wear on the group, because I've never given it this kind of workout in the past - 8 shots every morning it quite a busy La Pavoni. I will say that the group's piston seals are working great, and even though they did have a slight, stiff seal leak in March when I started they don't leak at all now.

I think a steam blocker like I previously used would also work well to keep the heating to a minimum, but I like the hot water heated group for it's temp stability and haven't turned back. Maybe once I run out of replacement o-rings I'll give it a try again!

Nice write up DanoM, just keep us posted