Air Brakes
Air Brakes tests the components and failure behavior of air-brake systems. You must know what warning signs mean and how to test the system before a trip.
Core rules
- The compressor builds pressure; the governor controls cut-in and cut-out. Tanks store air for service brakes and emergency spring brakes.
- Drain air tanks daily to remove moisture and oil. Keep the low-pressure warning working; it must activate before pressure falls below 60 psi.
- Spring brakes apply automatically when air pressure is too low. They are parking and emergency brakes, not a normal service brake.
- Test for leaks, check slack adjuster travel, and confirm the parking brake holds. Do not fan the brakes on a downgrade; use a lower gear and steady brake applications.
Worked example
Build pressure to governor cut-out, shut off the engine, and apply the foot brake. Watch the gauge. The warning buzzer must sound before pressure drops below 60 psi. If it sounds at 50 psi, the system fails the test because warning came too late. Reasoning: the 60-psi threshold gives the driver time to stop safely before spring brakes apply.
Traps
Pumping the brake pedal repeatedly on a long downgrade; ignoring a compressor that builds pressure slowly; and assuming the spring brakes will stop the vehicle gently rather than lock the wheels.