Which valve is responsible for protecting the primary circuit from the secondary circuit in a dual air brake system?

The spring brake modulator valve plays a crucial role in managing the interplay between the primary and secondary circuits in a dual air brake system. Its main function is to ensure that the primary circuit is protected from potential pressure loss or failure that might occur in the secondary circuit. This is vital for maintaining safety and control during braking, as it helps to prevent a total brake failure that could occur if both circuits were not managed separately.

By modulating the application of the brakes and allowing for selective pressure adjustments, this valve makes it possible to maintain some level of braking effectiveness, even if one circuit experiences issues. This redundancy is a fundamental aspect of dual air brake systems, enhancing the overall reliability of the braking process in vehicles equipped with such systems.