What is the easiest modification for the GCP, that is also the cheapest, and possibly makes the largest difference in extraction quality? That would be the simply 9 bar mod, at least in most people’s opinions. So I set out to try this mod myself recently.
How does the over pressure valve (OPV) work? The OPV is essentially a pressure gate. Water enters directly from the pump, and has 2 exits. All the liquid under the threshold of the spring will go to the brew group, and the pressure over that threshold will exit the OPV and land back in the water tank.
From the factory, the Gaggia Classic Pro comes outfitted with an OPV that contains a spring rated for 12 bars of pressure. This can easily be switched out for 9, 6.5 or 5 bar springs. When using a spring rated for lower pressures, the maximum pressure that is allowed to the brew group is therefore reduced to the amount of pressure the spring allows.
How to change the spring?
NOTE: be sure to unplug your machine before starting, and be sure the system is not pressurized.
Changing the spring is as simple as removing the two top screws on the machine lid, and moving the lid to the side. Then, pull the tube up and out of the water tank, which is attached to the overflow of the OPV. Using a 10mm wrench, loosen the brass nut connected to the output of the OPV. Carefully unscrew and remove the brass nut, being careful that the rubber knob inside the OPV does not pop out (usually is remains seated within the OPV). Then, switch out the spring, and reverse the process.
In my case, the results were pretty clear to see. The extraction had a smaller cone, had less channeling (fewer squirts), and the mouthfeel was better. The shots with the 9 bar spring seem more well rounded to me. For my palate, the 9 bar spring provided better results than the 6.5 and 5 bar springs as well.
For these tests, I used a bottomless portafilter, spring set from Shades of Coffee, Timemore scale, and Motta tamper, as well as a WDT tool.
Curious about the Gaggia Classic Pro? Check the links down below for information and pricing.