Hi, today i thought of a pavoni mod and i would like to know what you think about it and if it could actually work:
1) first of all, a simple replacement of thermostat with a pid to set precise brew temperature like a pump machine.
2) external cheap electrical air pump (5$) to create pressure inside the boiler to allow water to flow into the grouphead. The air pump is connected to the steamwand (or detaching the wand, directly to the steam hole) and manually turned on after opening the steam valve, then when the desired pressure has built inside the boiler, the steam valve is closed resulting in a boiler under pressure. Water is ready to flow into the grouphead when the lever is lifted up for preheat or making espresso.
For steam, the air pump is detached and the pid overridden by a second switch.

So, does it make sense to you this mod? It could work? Has anyone done a similar mod?
I read this, but it's a different way to build pressure inside the boiler:
Positive pressure, PID Pavoni: world domination begins

The trouble with doing anything like this is that all three La Pavoni groups are designed to have boilers that have ONLY water vapour in the space inside the system that is not liquid water. Pumping air therein results in uncontrollable boiler temperatures and parts of the system would become filled with air that are designed to be filled with water vapour.

All three also DEMAND that water entering the group must have more vapour pressure than ambient air pressure to drive air out from the space below the piston cylinder. i.e. the water MUST enter above the boiling point of water.

rpavlis wrote: Pumping air therein results in uncontrollable boiler temperatures and parts of the system would become filled with air that are designed to be filled with water vapour.

I don't understand this Why boiler's T is uncontrollable? It's controlled by a pid, not pressurestat anymore, so pressure is irrelevant, e.g. matadero210's mod (see link above). He also have boiler filled with air, and things work.

rpavlis wrote: the water MUST enter above the boiling point of water

again, see matadero210's mod: water enters at ideal brewing T, pushed in the group by positive pressure of 1,3 bar built in boiler by direct water supply. My idea of using an air pump is far more easy to do, reversible, and boiler pressure can be easily modified (this affects preinfusion pressure) between shots turning on the pump or letting air go outside opening steam knob.


Anyway, it's more easy to do it than to talk about it, so i've done it now: i attached a manual bike pump to the steam wand without the steam tip: hole size is perfectly compatible with presta valve. With a couple of stroke, i reached 1 bar inside the boiler, closed the steam knob trapping pressure inside (but it's not really necessary because pump has it's valve), raised the lever, and the water come out, cold of course, because the machine isn't turned on. So, it works Now la pavoni is turned in a caravel-peppina style machine, with just a 5$ pump.
There's some air leakage through group-boiler connection, maybe because i once detached the group and didn't sealed it enough, but now i can easily seal it in some way (grease or teflon tape).
Next step, i have to measure temperature behaviour, lowering the pressurestat at minimum, and doing experimental shots. Once things are verified to work, pidding is the last final step. Maybe it could be even unnecessary if lowering the pressurestat at minimum will get a good group temp stability and consistency without the overheating issue. It's because grouphead has some heat sink ability that could be usefull to lower a little bit the boiler temperature.

You can certainly give it a try and let us know how it goes. The La Pavoni, being a simple system, is easy to experiment with.

Few issues you might want to know
The La Pavoni group, at least on my 1984 pre-millenium, primarily heats up through the wet steam in the boiler. Even having dry air ("false pressure") will inhibit the heating up of the group. So if your group isn't heating up through wet steam it will have to heat through the contact with the hot boiler, which will take longer to warm up than the normal 10+ minutes.

Since it's a dipper tube the pressure from the air pump will drive the hot water into the group, but as designed the La Pavoni uses steam vapor to force out the cooler air and will then condense into water again as it cools in the group. You won't have that steam vapor, so your single pull shots could be smaller - not always a bad thing though.

It's quite possible that getting the whole system to run at a lower temp you can leave the La Pavoni on all day long and have it ready to pressurize and pull whenever you want. It's also possible the group might not heat up enough if you don't have the boiler at boiling or above.

Best of luck!

IMO, the primary difference between using air vs water pressurization is that water has a large cooling effect. But this can be beneficial in achieving some temperature drop.

Pre-treating the grounds with pressurized air to increase crema needs more study.

A PID controlled temperature sensor is always a good idea.

updates: i solved air leakage issue, now it's pretty airtight and the built pressure is stable.
I have a Millennium group, it works in this way:
http://www.linz.wright.name/pavoni/Pavo ... ection.png
It's heated by water, no wet steam. So pulling the lever up and down will bring hot water into the group, heating it in a matter of seconds at boiler temp.
But, even for pre-millennium groups, used in matadero210's mod, seems there isn't the heating problem of the group.
Positive pressure, PID Pavoni: world domination begins
The only difference in his successfull mod and what i'm doing, is the way to build the pressure inside the boiler. Mine is as simple as inflating a bike tire.

i've found some "litterature" about pumping air inside the boiler. I suspected i wasn't the only one to have this idea:
La Pavoni + PID = better temperature control?
He eventually found out that a pump wasn't necessary, and the only PID made a huge improvement.

PID'ing the Olympia Cremina
He mounted a micro pump (from a blood pressure monitoring device) and PID, successfull mod, very well done.
I also plan of using this type of micro pump because i have a broken blood pressure device to use.
One smart idea is that the pump can be controlled by the PSTAT no more attached to the heat element.

another link, same idea of using a bicycle pump, this dates 2005, 9 years ago:
https://www.coffeegeek.com/forums/espre ... nes/162257
quote "I am able to pull 10 shots after each other , each having the same taste and look profiles"
so, he's successfull with his air pump mod.

finally, also rpavils (who replied in this tread) used a presta bicycle tyre pressure gauge connected on the steamer with the tip removed, but for another reason, i.e. testing pressure release valve:
Testing pressure release valves for La Pavoni and others