Air Brake Test Pre-trip Inspection Procedures 2

Question 1

During a pre-trip air brake inspection, at what pressure should the low air pressure warning signal activate?

Accepted Answer

Before air pressure drops below 60 psi

Answer

The low air pressure warning device must activate before pressure falls below 60 psi, giving the driver time to stop safely before spring brakes engage at approximately 20–45 psi.

Question 2

What is the correct procedure to test the spring brakes during a pre-trip inspection?

Accepted Answer

Charge the system, chock wheels, release service brakes, pull the parking brake knob, and attempt to move the vehicle

Answer

With wheels chocked, fully charged system, and service brakes released, pulling the parking brake control should firmly prevent any vehicle movement — confirming the spring brakes are functioning.

Question 3

How do you test the tractor protection valve during a pre-trip inspection?

Accepted Answer

Close the shut-off valves on the rear, reduce trailer air pressure to trigger the valve, and confirm it closes

Answer

The tractor protection valve is tested by reducing trailer air pressure (by closing shut-off valves and draining air) until it drops to the activation range, confirming the valve closes to protect tractor air.

Question 4

What is the acceptable pressure drop rate with service brakes applied during the pre-trip air brake leak test?

Accepted Answer

Less than 3 psi per minute for single vehicles; less than 4 psi per minute for combination vehicles

Answer

FMCSA/CVSA standards allow a maximum leak rate of 3 psi/min for singles and 4 psi/min for combinations with service brakes applied; anything above is cause for repair.

Question 5

When inspecting the air compressor belt during a pre-trip, what should you check for?

Accepted Answer

Cracks, fraying, proper tension, and correct alignment

Answer

The compressor drive belt must be inspected for cracks, wear, fraying, proper tension, and correct alignment to ensure the compressor will maintain adequate air pressure.

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Air Brake Test Pre-trip Inspection Procedures 2