The maximum air pressure available for braking is determined by
- the foot valve.
- the brake chambers.
- the air pressure gauge.
- the air pressure in the tanks. ✓
Answer: D. the air pressure in the tanks.
The maximum air pressure available for braking is determined by the air pressure in the tanks.
Why this is the answer
The handbook describes compressed air as stored energy and says the air pressure gauges show how much pressure is in the vehicle's service air tanks. The foot valve and brake chambers use that stored air, but they do not create the supply limit. So the ceiling on what the brakes can get is set by tank pressure, which the gauges report. The passages do not spell out this exact sentence, so treat the link as a reasonable reading rather than a direct rule.
Why the other answers are wrong
- A. the foot valve. — The passages do not describe the foot valve as setting the air supply limit; they tie the gauge reading to pressure in the tanks.
- B. the brake chambers. — The passages do not say brake chambers determine the available pressure; they describe compressed air as stored energy and the gauge as showing tank pressure.
- C. the air pressure gauge. — The air pressure gauge only reports the pressure in the tanks; the passages do not say the gauge itself determines the maximum pressure available.
Remember it
The gauge is a reporter, not the source; the tanks hold the air.