Thank you for your help already in my purchase decision. In the end, I am the very happy owner of a Bezzera Mitica (vibratory pump).

Now I have a doubt regarding whether or not I should adjust the pump pressure of the machine.

The machine came adjusted to a factory 12 bar pressure. I have read comments pointing that a pressure of 9-10 bar is preferred. So far, that is clear.
But, after careful reading, I am not sure whether my machine is measuring 12 bar "closer to the pump" and it would be closer to 9-10 in the puck (so I do not need to adjust anything), or the measure represents approx. the pressure in the puck (so I should lower it).

I am getting similar pressure reading with the blind filter and during extraction, if this means anything.

Any input will be greatly appreciated.

If you wish to set it to 9 bars, you will need to purchase a modification kit.

I've seen it working with 12 bars without issues.

in the current parts breakdown manual for Magica (I owned a Magica for 2 years), there are two models of the OPV, at pages 8-9, TABLE 2A (up to 30.10.12), and at pages 10-11, TABLE 2A (from 31.10.12);
it appeared to me at the time, that the second version - the one which you probably have, on machines from 31.10.12, is easier to adjust for a lower pressure; without getting all those squeaking sounds!
actually, the Accessories manual does not include anymore the 9 bar OPV modification kit (which I've bought at the time);

you might try it, it's just a problem of unmounting the covers (6 screws: 4 on the bottom, and 2 on the left and right side, inside, up, front - (especially the last 2) you should only loosen them, no need to unscrew them completely);

lowering the pressure does not change dramatically anything in the cup, but does improve a lot against channeling - the machine would be more forgiving...
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the pressure gauge is showing the pressure immediately after the pump, so yes, you do not see the actual pressure above the puck!
however, as I measured it with a DIY portafilter with a pressure gauge, the pressure above the puck is lower than the value measured by the POMPA pressure gauge, but with less than 1 bar!

it is worth mentioning that at 12 bar, the pump gives an 130 ml/min flow rate (2,1 ml/sec), while, at 9 bar, the pump gives a 260 ml/min flow rate (4,3 ml/sec), meaning that at 9 bar there is larger by 2x flow rate margin, than at 12 bar: that would affect some normale to lungo shots, as the pressure would decrease to about... 9 bar, if the flowrate through the puck would increase to, say, 3.5-4ml/sec!

Thanks. I have done the adjustment and no issues. Apparently new Bezzeras can be adjusted without squeacking noises.

One question, just to understand it. Say I am trying to get 40ml in 25sec, thus I need much less than a flow of 4.1ml/sec at 9 bar, or I will fill up the cup in just 10secs...
How does it work then?