310T Air Brakes and Braking Systems 3

Question 1

What type of valve modulates air pressure to each wheel independently during ABS activation?

Accepted Answer

Modulator valve (ABS solenoid valve)

Answer

ABS modulator (solenoid) valves cycle between hold, dump, and reapply modes to control wheel slip at each monitored axle end.

Question 2

In a dual-circuit air brake system, which reservoir is pressurized first by the compressor?

Accepted Answer

Wet (supply) tank

Answer

Air from the compressor flows first into the wet (supply) tank where moisture collects, then through check valves into the primary and secondary circuit reservoirs.

Question 3

What is the minimum air pressure at which the low-pressure warning device must activate per FMCSA regulations?

Accepted Answer

60 psi

Answer

FMCSA (49 CFR 393.51) requires the low air pressure warning to activate before reservoir pressure falls below 60 psi.

Question 4

A relay valve is used in air brake systems primarily to:

Accepted Answer

Shorten brake application and release time for remote chambers

Answer

Relay valves use a small control signal from the brake treadle to open a local large-volume air supply to remote brake chambers, reducing lag time.

Question 5

On a combination vehicle, which valve automatically closes to protect the tractor air supply if trailer air pressure drops rapidly?

Accepted Answer

Tractor protection valve

Answer

The tractor protection valve senses a sudden drop in trailer supply line pressure and shuts off air flow to the trailer, protecting tractor system pressure.

(310t) Truck and Coach Technician Certification Practice Test

(310t) Truck and Coach Technician Certification Practice Test

310T Air Brakes and Braking Systems 3