I've been using Rocket Cellini V2 for 6 months.
The brew pressure gauge is always indicating 10 bar when I pull a shot.
If I grind coarser, the shot goes fast(2 oz for 20 seconds), but the gauge indicates 10 bar.
It also indicates 10 bar with blind filter.
10 bar is not bad, but I feel the taste is a bit strong.
So I tried to lower it by adjusting OPV.
I opened the cover.
Here is a picture.
I guess OPV is in white circle.
The mystery is a black valve in blue circle.
So I e-mailed Rocket, questioning the function of black valve.
Here's the reply.
But I cannot understand the black valve's function.The valve you mention is solely for the pump pressure gauge on the vibration pump machines.
Closing the valve allows for the technician to correctly set the expansion valve
As a vibration pump pressure is regulated by the expansion valve setting, a pump pressure gauge is not strictly necessary. This valve allows the by pass to be correctly set while indicating the pump pressure. The valve should be set as it was when you received.
Any comment will be appreciated.