Air Brake Test Study Guide 2026

The air brake system is designed to operate between approximately 100 psi (cut-in) and 125 psi (cut-out), the range maintained by the governor.

Compressed air naturally contains moisture, which condenses into water inside the air tanks. Draining the air tanks daily is essential to remove this accumulated water and any oil contaminants. This practice prevents rust and corrosion within the air brake system, which can lead to component failure, reduced braking efficiency, and costly repairs.

The wet tank receives air directly from the compressor and is the collection point for moisture and oil. Air then passes through a check valve into the primary and secondary supply tanks.

Greater vehicle mass means significantly more kinetic energy at the same speed, requiring more braking force and distance to stop.

The air brake system's governor is designed to control the compressor's operation, ensuring adequate air pressure. It should trigger the compressor to resume pumping air into the reservoirs when the pressure drops to approximately 80 psi (552 kPa). This 'cut-in' pressure ensures that there is always sufficient air for safe braking, preventing the pressure from falling too low.

Poor traction and bad weather require increasing your following distance for safe stopping.