Zarówno w GC jak i w Unice spróbowałem ustawienia pompy na 9 i 10 bar, jak dla mnie bez większego sensu.
Zastanawiało i dziwiło mnie zawsze jak użytkownicy zmieniając ciśnienie odczuwali WIELKĄ poprawę w smaku 
Polecam filmik...
Pozdrawiam.
Dodam jedno bez NPF nie dowiesz sie.
Ten komentarz podsumowuje, bullshit reasoning filmu:
You missed quite a bit, I'm afraid, on how the pump works. You are right on puzzling about how the extraction can stay the same (it can't
Here's how a normal espresso machine with a vibration pump works:
- Ulka pumps operate at 17 bar, which is way too high, and the pressure varies with the flow. An Ulka pump can sustain 17 bar at very small flows, 13 bar at 100cc/min, 11 bar at 180 cc/min, 5 bar at 400 cc/min
- the pump output is fed into an OPV (overpressure valve) that "lets thru" only 9 bar, no matter what the flow (as long as it's below the max flow that an Ulka pump can sustain, which is 260cc/minute at 9 bar)
- the excess water is fed back into the water reservoir
- the output of the OPV (9 bar) is then fed into the boiler/heat exchanger, then into the brew head
Every espresso machine in the world with a vibration pump has an OPV set at 9 bar, for 2 very good reasons: real espresso is defined by brewing at 9 bar, and a Ulka pump limited to 9 bar by an OPV can easily sustain the flow required by an espresso (the Espresso guidelines are 50 cc for a doppio in 25 seconds, 120 cc/min)
By setting the OPV at 11 bar, you only make things worse for the poor Ulka pump. At 9 bar, an Ulka pump is capable of 260cc/min, and we only ask to use 120 cc/min, with a high safety margin for any loss in the system. At 11 bar, the Ulka pump can only sustain 180cc/min, and we ask 120cc/min, only a small margin easily offset by losses in the system
Let me repeat: the OPV valve (the element set differently by Bezzera) is after the pump. It does nothing to help the pump, quite the contrary. A rotary pump is set to 9 bar, fed into the boiler/heat exchanger, then the brew head.
As you can see, at the boiler/heat exchanger input, 9 bar from an OPV look exactly the same as 9 bar from a rotary pump. If the OPV is set at 11 bar, you get 11 bar at the brew head,and a different espresso.
If you look at the link I posted, you can see I tried adding a brew head pressure gauge, and any other espresso machine shows 9 bar (rotary or vibration) with the 50cc/25 second flow, the BZ10 shows 11 bar in the same conditions (before adding the kit Bezzera now sells)
Setting the OPV at 11 bar causes the espresso to be brewed at 11 bar. What Luca says is completely wrong, and the fact that they finally sell the kit should be proof enough of them realizing the problem.
If Luca said "I like espresso brewed at 11 bar, and I set all my machines at 11 bar", I'd agree and respect that (even if I like espresso at 9 bar better). But his pseudo explanation of why small pumps need 11 bar is entirely bogus. If anything, setting an OPV at 11 bar is worse for a small vibration pump
