What pressure causes the governor to place the compressor in the "unloading" stage?

Answer: C — Between 115 and 135 psi

The governor's role in the air brake system is crucial for maintaining optimal pressure levels in the air tanks. When the pressure in the system reaches a range between 115 and 135 psi, the governor recognizes that the air supply is adequate and transitions the compressor into the "unloading" stage. This means that the compressor stops pumping air into the tanks, preventing over-pressurization and maintaining the system's efficiency. In this range, the system is efficiently managing the air pressure necessary for the operation of the brakes, ensuring that the brakes can function properly without the risk of failure due to excessive pressure. Understanding this optimal pressure range helps operators manage their air brake systems effectively, contributing to safer vehicle operation.