What is the Training Disc? What is its purpose, why does it rupture, and how do I replace it once it does?
Each Flex comes with a Training Disc already installed on the underside of the Piston. As a fail-safe, this Training Disc has been incorporated to protect the Flex frame from excess force, as users dial-in their espresso. If the silver foil is ruptured, the valve will bleed pressure (and water) up and through the piston. If this occurs, the valve should be replaced, as below*.
The NEO Flex comes with one Pressure Release Valve replacement, standard.
Note: If the foil has ruptured, this would indicate that pressure is too high within the brew head. Grind coarser to prevent a reoccurrence.
If you feel confident that your grind size and lever pressure is dialed-in, and that you are not at risk of applying excess force to your Flex while brewing, you may consider swapping in the Graduation Disc. This is a solid disc alternative with no foil.