What is the primary function of the two-way check valve in the air brake system?

Answer: B — To allow dominant pressure to activate some controls

The primary function of the two-way check valve in an air brake system is to allow the dominant pressure to activate certain controls. This means that the valve will permit airflow in one direction while blocking the reverse flow, which is crucial for maintaining proper pressure in different parts of the system. By doing so, it ensures that air pressure needed for activating various components, such as brake chambers, is available while preventing any potential backflow that could disrupt the system's functionality. In an air brake system, it's essential for the control mechanisms to receive the correct pressure to function effectively. The two-way check valve plays a vital role in maintaining this required pressure, ensuring the brakes can be applied smoothly and safely when needed. Understanding this function is important for technicians as it impacts the overall reliability and responsiveness of the braking system.