What component is responsible for sending pressure to the main wheel brakes?

The master cylinder is the correct answer as it plays a crucial role in the hydraulic brake system of the aircraft. When the pilot presses the brake pedal, this action activates the master cylinder, which generates hydraulic pressure. This pressure is then directed to the main wheel brakes, allowing for effective braking performance. The master cylinder essentially converts the mechanical force from the brake pedal into hydraulic pressure that can influence the brake system.

In contrast, while the brake pedal initiates the process, it does not directly send pressure; rather, it serves as the control mechanism for the master cylinder. The hydraulic valve controls the flow of hydraulic fluid but does not generate or send pressure itself. The pressure regulator is primarily concerned with maintaining consistent pressure within the system rather than sending pressure to the brakes.