The maximum air pressure available for braking is determined by
- the air pressure gauge.
- the air pressure in the tanks. ✓
- the foot valve.
- the brake chambers.
Answer: B. 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 says most air brake systems operate at a maximum pressure of about 125 p.s.i., and the governor stops the compressor once enough pressure has been built. It also restarts compression when pressure in the tanks drops, such as after repeated brake applications. That makes the pressure held in the tanks the air supply the braking system has to work with, while the governor controls the compressor based on tank pressure.
Why the other answers are wrong
- A. the air pressure gauge. — The gauge is not described as setting the maximum pressure; it is not the source of the air supply.
- C. the foot valve. — The foot valve is listed as a system component, but the passages do not say it determines the maximum pressure available.
- D. the brake chambers. — The passages do not describe the brake chambers as setting the system's maximum pressure.
Remember it
Think of the tanks as the air reservoir: the governor fills them to the system limit and restarts when tank pressure falls.
Official handbook: ICBC Driving Commercial Vehicles, 8 Air brakes – Governor, p. 152