Gaggia Classic Pro OPV Spring Mod (9 bars)
The Gaggia Classic Pro comes from the factory with an OPV that opens at 12-14 bars which is much higher than the standard 9 bars that is typically recommended for espresso extractions. It is set this way in order to improve extractions when using the pressurized basket, but that is not ideal if you are using a standard basket.
This spring will reduce the OPV pressure by 3 bars, bringing it down to 9-11 bars (depending on your machine).
Note: This is for machines with the black plastic OPV.