What device multiplies brake force and decreases the effort required from the driver?

The device that multiplies brake force and reduces the effort required from the driver is the Power Booster. This mechanism enhances the effectiveness of the braking system by using hydraulic pressure to amplify the force applied by the driver on the brake pedal.

When the driver presses the brake pedal, the power booster utilizes engine vacuum or hydraulic pressure to increase the force acting on the brake system without requiring the driver to exert significantly more effort. This allows for smoother and more controlled braking, making it much easier for drivers to stop the vehicle quickly and safely.

Both the Vacuum Assist Booster and the Power Booster serve similar roles in utilizing vacuum to enhance braking efficiency, but generally, "Power Booster" refers more broadly to systems that can incorporate various methods to assist in brake force multiplication, which may include hydraulic systems in conjunction with vacuum aids. The Return Spring is primarily used to return the brake components to their original position after braking and does not directly multiply brake force. The Spool Valve is more associated with controlling fluid flow in hydraulic systems and does not function to amplify brake effort in the same way as a power booster does.