I have noticed something strange on my pavoni. When I pull the lever down, there is no resistance until it is half way. I hold it in the open position for 10 seconds before extracting. Once it reaches the horizontal point, it behaves like I would expect it. The result is 10-15ml in the cup at most. Is there something wrong with my technique? Which I think is the case. Or my machine? It doesn't draw any more water if I hold the lever up for any longer.
I usually let the machine warmup for 15-18 minutes. It draws water fine without the pf in place. I dose so there is a 4-6ml gap from puck surface to top of basket. It is an older machine, circa 1970's.

Any help or if you need any more info let me know.

Cheers, Jason

This site may help you trouble shoot what is going wrong.

http://www.pavoniexpress.com/

I am not sure what the problem could be, as I am still quite the newbie where levers are concerned. The site above has a great trouble shooting guide, with many upon many different issues that may be happening.

Hope this helps.

Thanks for the link, it sounds like the piston has dropped. I'll have to open it up and have a look when I get a day off. I'll keep you posted.

Hi PR,

I have the same problem, and even though I did not (yet) fix it, this is my current thinking.

First off, the problem is intermittent---sometimes it happens, sometimes it doesn't. I don't think it's a mechanical issue. What I notice is that when this happens, there is a lot of air in the piston chamber after pulling the shot, which raises the lever if I let it go immediately afterwards (and would cause a little explosion if I were to remove the portafilter immediately, which is not a good idea).

So it seems obvious that the piston chamber draws air when pulling up the piston. That air keeps the water from flowing in, and will only slowly get released after the shot. The air can really only come from two ends [*]---either from the top of the piston past the two rubber piston seals inside, or from the bottom, through the portafilter or past its seal against the group head.

I think the latter is more likely. If the piston seals would let air through, they would let the air go on pushing the piston down [**], but at least in my case the air cushion remains inside until after the shot. I guess it's possible that moistening the rubber improves their seal, which is consistent with the observation that the problem is much more likely to occur on the first shot than on subsequent ones. But for the moment my money is on the PF/group seal, as that is the one that is exposed and thus more likely to be affected by outside influences (e.g. it can get soiled by coffee grounds etc.).

It's amazing how complicated the failure modes of such a simple device can be...

Cheers,

-- j



[*] When first using the machine, or after a break, there is also a small amount of air in the pipe connecting the tank with the group, but assuming that you flush that pipe initially, that should be gone.

[**] There is one effect that occurs rarely, but which I find very confusing: Occasionally, on pushing the lever down, something "bubbles" inside the piston chamber, letting the piston go down a long way without much resistance. It's almost as if water is rushing past the piston seals, althoug I am not sure that that is the case.

jwj wrote:Hi PR,

...First off, the problem is intermittent---sometimes it happens, sometimes it doesn't. I don't think it's a mechanical...

Try to raise the lever letting the water flow in the group while the boiler it's on and it is near the shut down. I noticed that in this way there will be less air in the group, let me know your results

pab wrote:Try to raise the lever letting the water flow in the group while the boiler it's on and it is near the shut down. I noticed that in this way there will be less air in the group, let me know your results

This is exactly what I do with my Gaggia Factory. I start the pre-infusion at the start of the cycle. Also, doing "mini pumps" helps increase pressure at the lever before actually pulling the shot.

The max. boiler pressure of my machine is currently set at 0.75 bar. I was told by an experienced Pavoni service person I need to increase it to 1.0 bar to get more resistance at the lever.

Javier wrote:The max. boiler pressure of my machine is currently set at 0.75 bar. I was told by an experienced Pavoni service

Mine is at 0.9 (factory setting)

I'm pretty sure its me now. The problem must have been air bubbles. I tried the mini pumps and also have been doing a longer flush, this seems to have solved some of the no resistance problem, and the short shots. Its still very hit and miss, my dose and tamp seems to have a big effect on the espresso volume which I put down to the absorbtion rate of the coffee with more of it or harder tamp.

Ok, some more experimenting this morning. I've managed to somewhat solve the resistance problem with the mini pumps. I've also started raising the lever until just before the water enters the group before locking in the Pf. I'm getting much better pour legnths and the resistance issue being resolved is allowing me to get longer time for my pours. Today I dosed much higher, figuring the 4mm clearance difference would make minimal effect to the amount of water entering the group. I'm still not covinced about multiple pulls, but I tried to use the lever to push some water into the coffee puck and opening the group valve again to allow a bit more water in. The result was a good pressure all the way through the shot, and about 1-1.5 oz espresso. On that pull though I saw signs of channeling for the first time in my puck.
From here on it may just be alot of experimentation before I decide on a technique.

Also realize that with multiple pulls, the brew temperature is much higher on the subsequent pull, resulting in more bitter espresso.