A driver notices that when the parking brake is applied, the primary air tank pressure drops significantly, while the secondary tank pressure remains stable. What does this indicate?
- AA leak in the secondary air system.
- BA faulty air compressor.
- CNormal operation, as the parking brake uses secondary air.
- DA leak in the primary air system, likely related to the parking brake control valve or lines.
Show answer & explanationAnswer & explanation
Correct answer: D. A leak in the primary air system, likely related to the parking brake control valve or lines.
The parking brake (spring brakes) typically releases by air pressure supplied by the primary air system. When the parking brake is applied, if the primary tank pressure drops significantly and the secondary remains stable, it points to a leak specifically within the primary system's parking brake circuit, such as the parking brake control valve or its associated lines.
Why the other options are wrong
- A. A leak in the secondary system would cause its pressure to drop, not the primary's.
- B. A faulty compressor would affect both tanks' ability to build/maintain pressure generally, not just the primary when the parking brake is applied.
- C. The parking brake typically uses air from the primary system to release. A significant drop in the primary tank pressure upon application (which means releasing air to engage the spring brakes) indicates a leak, not normal operation.
Parking Brake Air Supply
The parking brake (spring brakes) typically uses air pressure from the primary air system to keep them released. A pressure drop in the primary tank when applying/releasing the parking brake can indicate a leak in that circuit.
- Primary system often supplies parking brake air.
- Spring brakes engage when air pressure is lost.
- Air is used to 'hold off' the spring brakes.
Memory trick: Park with primary air, leaks make it scary.