What is purpose of master cylinder piston primary cup?

The primary cup of a master cylinder piston serves as a seal that prevents brake fluid from leaking out of the master cylinder while also allowing the piston to create hydraulic pressure when the brake pedal is pressed. It ensures that the brake system maintains the necessary pressure for effective braking, while also helping to return the piston to its original position when the brake is released. Proper function of the primary cup is crucial for the reliability and safety of the braking system.