6. If the air compressor should develop a leak, what keeps the air in the tanks?
Detailed Explanation
The one-way check valve allows compressed air to travel toward the reservoirs while preventing stored air from flowing backward toward the compressor. If a leak develops on the compressor side of the valve, the valve helps isolate the air already stored in the tanks. It does not repair the leak or create new pressure, so the defect still requires service.
Official reference: FMCSA Commercial Driver License Manual, Section 5: Air BrakesCorrect Answer: The one-way check valve.
Why This Matters on the CDL Test
Separate air-storage components from combination-vehicle protection components. The check valve protects air already in the reservoirs; the tractor protection valve protects the tractor air supply from a trailer breakaway or major trailer leak.
How to Remember It
One-way means one direction: air can enter the tank, but it should not flow backward toward the compressor.
Answer Review
"The one-way check valve" is correct because its job is to permit flow in one direction and block reverse flow. That protects reservoir pressure from escaping back through a leaking compressor supply path.
Why the other answers are weaker
- The tractor protection valve.This valve protects the tractor air supply when trailer air lines separate or develop a serious leak; it is not the reservoir check valve in this question.
- The emergency relay valve.A trailer emergency relay valve helps apply trailer brakes and manage trailer reservoir air; it does not stop tank air from flowing back through the compressor supply line.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Air Brakes.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
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52. The governor controls when the air compressor will pump into the air storage tanks.
An air compressor governor will stop the compressor from pumping air once the air tanks have an air pressure level of:
1. Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?
106. If your truck's air compressor has its own oil supply when should you first check the oil level?
13. If your truck has a properly functioning dual air brake system and minimum size air tanks, the air pressure should build from 85 to 100 psi within _ seconds?
Keep Studying Air Brakes
Question pages help you review one rule at a time. To build test-day speed, move back into the full Air Brakes practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.