Michigan CDL - Air Brakes Practice Exam

What is the function of a one-way check valve in an air brake system?

1. To increase air pressure

2. To prevent air from escaping

3. To allow more air into the system

4. To release excess pressure

The correct answer is: To prevent air from escaping

In an air brake system, a one-way check valve serves the essential function of preventing air from escaping the system. This is crucial for maintaining the air pressure necessary for effective braking. When the brakes are applied, it is important that the air pressure remains consistent to ensure that the brake components, such as the brake chambers, receive the required air pressure to activate properly. The check valve allows air to flow in one direction — towards the brake system components — while blocking any backflow of air that could result in pressure loss. This mechanism ensures that the brake system remains fully pressurized and operates reliably, especially in situations where air pressure is critical for safe braking. The other options provided focus on functions that are not relevant to the role of a one-way check valve. For example, increasing air pressure or allowing more air into the system does not align with the valve's function, as these tasks would be managed by a different component within the air brake system. Similarly, releasing excess pressure is not a function of a check valve, as that could potentially disrupt the necessary pressure levels needed for braking efficiency.