I agree with Professor Pavlis - the anti-vac is not worth the cost and trouble of adding as an upgrade. If your seals are tight, when the machine cools the atmospheric pressure will push air through the screen up into the chamber, which will cause the ghostly effect of the lever slowly rising on its own. But as long as the PF is empty and clean there should be no concern about stuff getting back above the screen or into the boiler.

On a bigger machine on a timer, an anti-vac is helpful because you avoid the need to bleed air from the boiler then wait a long time for it to fully heat the group up when pulling that first morning drink. On a little Pavoni it hardly matters because it's so easy and quick to make the steam/air purge part of your first shot routine.

rpavlis wrote:If you got the machine from a friend locally, be careful of the water that you use after you get this machine all back into order. Many machines come to an early end from use of water with certain contaminants. I like 1.0 mM potassium bicarbonate in purified (distilled or deionised) water. It buffers pH and can adjust relative extraction of basic and acidic coffee contaminants. It also keeps the water slightly alkaline, the most stable situation to prevent corrosion, it also will NOT produce scale at all. Do not worry about not having Ca and Mg in your water, there is far more of these elements in the beans than you would get from the water!!!!

Would you mind sharing a little more information on adding Potassium Bicarbonate to distilled water? My search for Potassium Bicarbonate on Amazon and eBay, came up with a bag labeled for wine making. It does not say "food grade," even though I suspect that if it can be used for wine, it could be used for food. It also doesn't state its purity. Can you tell me more about the quality I am looking for and how much to add in a gallon of water?

Thank you for your help.

Please can you explain this also for a eu metrics ? How much is 1.0 mM?
Also regarding group walls where the piston goes, I am not able to find similar product of "silicone" Dow 111 in EU. At least can you list me the product on amazon maybe?
As well I need to lubricate the external parts of the lever with an high quality grease, not the silicone.

Can you maybe suggest to me some similar products I can buy in EU? Maybe UK? Germany?

Anyway, thank you for explaining the auto bleeding issue. I am not going to change my safety vault, rather I will clean portafilter and screen right after the shot.

It's also called Molykote - if that helps. I bought a little tub of it off eBay for a small price. I wouldn't think the shipping would be too much.

yes I found it, thank you.. 100g tube for around 20eur. I guess that's overpriced, but well when I take a shipping cost into account it will be same. There are cheaper kinds, but everybody is suggesting this one all over the forums, so I will stick with that one since it is tested and approved.

mM means millimoles per litre. The molecular weight of potassium bicarbonate is 100g/mole. (Which also means 100mg/millimole) Thus 1mM potassium bicarbonate means 0.1 gram/litre. It is easy to make a 10% solution of potassium bicarbonate by dissolving 10 grams of it in perhaps 70 mL of water, and then adding enough water to it to make 100 mL total volume. If one take 1 millilitre of this and add it to a litre of water it gives 100 mg/litre or 1 mM KHCO₃.

You could use NaHCO₃. Its molecular weight is 84 g/litre. However, you cannot make a 10% solution of it because it is not soluble enough. You could however, make a 5% solution of it by dissolving 4.2 grams of it and getting 100 mL by adding water. You would need to add 2 millilitres of this to get near 1 millimolar. To me this seems to create a slight flavour change, so I prefer potassium. Wine makers use potassium bicarbonate to reduce acidity. They use the potassium salt to keep sodium out of their wine, and also to help precipitate potassium tartrate which is present in grapes.

You can use lower concentrations than 1 mM, I sometimes use 0.5 mM KHCO₃ which involves adding only 0.5 mL of the 10% solution per litre.

Generally I mix it in a 4 litre plastic bottle. Scale will never form, and this produces about the most stable possible aqueous solution for brass and copper. Again, bicarbonate free water tends to result in more acidic espresso, and changes what extracts a bit.

Thank you, Robert.

It sounds like the Potassium Bicarbonate labeled for use in wine would work fine.

Yes, the potassium bicarbonate sold for making wine is ideal.

You may find a slight precipitate forms when a 10% solution of potassium bicarbonate stands for a while. This precipitate is harmless. It is actually a bit of potassium sesquicarbonate. Its formula is K₂CO₃*2KHCO₃*3/2H₂O. It forms because it has a more stable crystal latice than either potassium bicarbonate or potassium carbonate. It does not form in less concentrated solutions of potassium bicarbonate.

I just mixed up 4 litres this morning.

And what do you do with this precipitate? Do you filter it out or do you add it together with solute?

The amount of the precipitate is slight. I just let it stay at the bottom of the storage bottle, and if any get into the water it does not matter, because it dissolves. I have used this technique for a long time. You can experiment with the amount of potassium bicarbonate you add to get the flavour result you want. Unlike depending on city water compositions, you can control it to specifications.