Final answer:
When the brake chamber of an S-cam drum brake system fills with air, the push rod is pushed out, moving the slack adjuster and rotating the S-cam to apply the brakes. This system differs from hydraulic brakes, which utilize Pascal's principle to amplify force applied to the brake pedal through hydraulic pressure.
Step-by-step explanation:
With S-cam drum brakes, when the brake chamber fills with air, air pressure pushes the push rod out, moving the slack adjuster and thus rotating the S-cam. This action causes the brake shoes to press against the drum, resulting in friction which slows down the wheel. The system's operation is fundamental to vehicle safety and relies on the principles of hydraulics and mechanical advantage.
The brake system typically includes a series of levers, rods, and the brake drum itself. The S-cam drum brake is named after the S-shaped cam at the heart of its design. The brake chamber's expansion is an application of fluid power, where compressed air takes the place of liquid in Pascal's principle, which states that pressure applied to a confined fluid is transmitted undiminished in all directions.
In contrast to hydraulic brakes, which were described in Figure 14.18 utilizing Pascal's principle, air brake systems like the S-cam drum brake use compressed air to transfer force. Hydraulic brakes apply the principle where a force exerted on a pedal increases through a lever and is then further amplified by the hydraulic system, resulting in equal pressure being transmitted to the wheel cylinders. The effectiveness of both hydraulic and air brake systems depends on proper force transmission and component functioning.