CDL Air Brakes TestAir Brake System PartsHard
A driver observes that the air pressure gauge for the primary air tank is consistently reading 10-15 psi lower than the secondary air tank gauge, even after the compressor has built full pressure. Both gauges appear to be working. What is the most likely cause?
- AA faulty check valve between the primary and secondary tanks.
- BA malfunctioning air compressor governor.
- CA partially restricted air line to the primary tank's gauge.
- DAn internal leak within the primary air tank.
Show answer & explanationAnswer & explanation
Correct answer: A. A faulty check valve between the primary and secondary tanks.
In a dual air brake system, check valves separate the primary and secondary air circuits. If the check valve between the tanks is faulty (e.g., partially blocked or leaking), it can prevent equal pressure distribution, causing one tank to consistently show lower pressure even if the compressor is working.
Why the other options are wrong
- B. A malfunctioning governor would affect the overall system pressure build-up or cut-out, usually affecting both tanks similarly or causing over-pressurization.
- C. A restricted line to the gauge would cause an inaccurate reading, but the question implies both gauges are 'working' and the discrepancy is consistent, suggesting a system pressure difference, not just a gauge issue.
- D. An internal leak within the tank itself would cause the pressure to drop over time, not necessarily a consistent 10-15 psi difference while the compressor is running and building pressure.
Dual Air Brake System Check Valve
Valves in a dual air brake system that prevent air from flowing from one tank or circuit to another, ensuring independent operation and preventing total air loss from a single leak.
- Maintains separate pressure in primary and secondary circuits.
- Allows air to flow in one direction only.
- Critical for safety in case of a single circuit failure.
Memory trick: Dual tanks, separate paths, check valves keep them apart!