CDL Air Brakes TestDual Air Brake SystemsEasy
A driver is performing a pre-trip inspection on a commercial vehicle equipped with a dual air brake system. They notice that the primary air gauge reads 100 psi, but the secondary air gauge reads 60 psi. What is the most likely cause of this discrepancy?
- AA malfunctioning brake pedal valve
- BA leak in the secondary air system
- CAn over-pressurized primary air tank
- DA faulty air compressor governor
Show answer & explanationAnswer & explanation
Correct answer: B. A leak in the secondary air system
A significant difference in pressure between the primary and secondary air systems, especially when one is considerably lower, strongly indicates a leak in the system with lower pressure. The air compressor should fill both systems, and the governor regulates overall pressure.
Why the other options are wrong
- A. A malfunctioning brake pedal valve affects air application to the brakes, not the static pressure in the tanks themselves.
- C. An over-pressurized primary tank is unlikely without an issue affecting the governor or safety valve, which would be a more general problem.
- D. A faulty governor would typically affect both systems or prevent any system from reaching full pressure, not just one.
Dual Air System Pressure Discrepancy
A noticeable difference in air pressure between the primary and secondary air systems often indicates a leak in the system with lower pressure.
- Each system has its own gauge.
- Significant difference points to a leak.
- Compressor fills both systems.
Memory trick: Separate gauges, separate troubles, separate fixes.