Which part transfers force from the diaphragm to the master cylinder?

The power piston is the component that transfers force from the diaphragm to the master cylinder in a brake system, particularly in vacuum-assisted braking systems. When the brake pedal is pressed, atmospheric pressure pushes down on the diaphragm, creating a vacuum that allows the diaphragm to move. This movement activates the power piston, which then pushes forcefully on the master cylinder’s piston.

The efficiency of this transfer is crucial because it directly affects how much braking force is generated. The power piston amplifies the force applied to the brake pedal, making it easier for the driver to operate the brakes with less effort. This component plays a vital role in ensuring that the braking system can effectively slow down or stop the vehicle when needed.

The other components mentioned, such as the spool valve, lever, and return spring, serve different functions within the braking system. The spool valve manages brake fluid flow, the lever typically helps in the mechanical advantage of activating the brakes, and the return spring assists in returning components to their original positions after braking. While all these components are important, the power piston is specifically responsible for the critical transfer of force to the master cylinder.