La Pavoni-Mini Rubber Gasket

#1: Post by **leverfun** » June 22nd, 2021, 2:29 am

Can someone here tell me what the 'Shaft Seal' in the grouphead of la pavoni does? It is the small white gasket that is a the top of the grouphead that is secured in place with a clip and washer. My machine seems to be both missing it and a space to put a replacement. My guess is that this problem is affecting the pressure in the grouphead resulting in horrible channeling. Visual inspection of the puck reveals many holes, and coffee taste horrible-thin and uneven. These problems pre-dated a recent replacement of the shower screen, o-ring and piston seals. I thought these might have been the source of the channeling, but I can now eliminate these. So, I am wondering if the problem is with the mini gasket.

This is the shaft seal:

https://coffee-sensor.com/product/la-pa ... 6-1186470/

#2: Post by **ojt** » June 22nd, 2021, 2:52 am

That particular seal makes sure the pressurized water does not leak up and out of the shaft hole. You must have some kind of sealing there now, without it you'd have a constant leak.

I do not think that has to do much with channeling though, that would be a symptom of some other issue. I know the pre-mill Pavonis can overheat very easily and often you also have a strong jet of water from between the inlet hole and the piston, which leads to fracturing of the puck (holes) and channeling. You could try to:

- Raise faster over that point
- Tamp harder
- Make sure you are not pulling too hard.. it shouldn't feel like a workout
- Make sure your boiler pressure isn't too high. 0.8 to 1.0 bar is usually a good standard, I think perhaps even closer to 0.7/0.8 with the pre-mills
- One surefire way to reduce puck fracturing is to us a screen over the puck, such as the one from BPlus or perhaps also just a disc cut from coffee filter paper

What grinder are you using? A good quality, even grind is very important with espresso in general but I read perhaps even more so with a Pavoni

June 22nd, 2021, 4:48 am

Thanks ojt.

Here are the results of some trials:
1.The puck seems to develop problems even in the first 2-3 secs of the pre-infuse. So, presumably, the channeling isn't from applying too much pressure.
2. I tried over tamping, under tamping, and 'normal' tamping. Didn't seem to make much difference. (I have tried this previously.)
3. I have tried both gently as well as quickly letting in the water-having purged well the boiler. And, I still got significant channeling.
4. Last, I tried the coffee filter paper screen over the puck. And, the puck still channelled!

A few other details:
1. I have a post-2000 machine. So, pressure in the boiler is generally stuck at 1 bar.
2. My grinder is a mini mazzer, and I de-clump. So hopefully there is no problem there.
3. I recently upgraded to the IMS basket and shower screen. But, my sense is that the water is still coming out unevenly from the shower screen. That is why I thought it might be that gasket.
4. And, to confirm, I have nothing in the place where the shaft seal goes. I have taken the group head apart a few time to double-check!

Any thoughts are very welcome. I would love to have my la pavoni back working

#4: Post by **RobAnybody** » June 22nd, 2021, 5:12 am

on most pavonis the pressurestat can be adjusted (for instructions just use the search function on this website)
the shaft seal is hidden inside at the top of the grouphead
underneath a c clamp and a flat brass ring, it can be difficult to see. (see also here: http://www.francescoceccarelli.eu/La_Pa ... po_eng.htm)
If it were badly worn you would see water at the shaft.
one quick obvious question, how old are the beans you are using?
cheers,
Rob

June 22nd, 2021, 10:49 am

Hi Rob,

I can see the place for the C clip and flat brass ring-but there is nothing there. But the shaft seal doesn't have anywhere to slot in underneath. Also, it seems strange that there wasn't anything in there when I opened the group head-no C clip, flat brass ring nor a shaft seal. There is definitely nothing up there. I wonder if anyone else has had this issue.

The beans between 7-14 days old.

#6: Post by **Marcelnl** » June 22nd, 2021, 11:24 am

overdosing is also a great way to get channeling, did you check/decrease the dose?

#7: Post by **RobAnybody** » June 22nd, 2021, 11:44 am

leverfun wrote:I can see the place for the C clip and flat brass ring-but there is nothing there. But the shaft seal doesn't have anywhere to slot in underneath. Also, it seems strange that there wasn't anything in there when I opened the group head-no C clip, flat brass ring nor a shaft seal. There is definitely nothing up there. I wonder if anyone else has had this issue.

that is weird indeed, do you have any pictures?

3. I recently upgraded to the IMS basket and shower screen. But, my sense is that the water is still coming out unevenly from the shower screen. That is why I thought it might be that gasket.

have you tried grinding a bit coarser and using a lower dose? To little headspace will promote channeling as does having a very fine grind in combination with the more open surface of the IMS basket.
Do you use the late-lock in technique? (raising the lever untill you hear hissing, lower a bit after the first drops of water and then lock in the portafilter)
cheers,
Rob

June 24th, 2021, 10:37 am

Hi Rob,

Thanks, late-lock in technique + fliter paper was the fix. But i'm still wonder where the shaft seal went.

But I am getting a few great shots now!

Michael