Why are there two service tanks in a modern air brake system?
- For efficiency
- For fuel economy
- For safety ✓
- For greater stopping power
Answer: C. For safety
There are two service tanks for safety: they create two separate air circuits so one can still provide braking if the other fails.
Why this is the answer
The handbook describes the primary and secondary tanks as dual-service tanks that split the air supply into two separate delivery circuits. It calls having two circuits a safety feature: if one circuit fails, the other still provides enough brake function to stop the vehicle. That is why the bank answer points to safety, not to how smoothly or economically the vehicle runs. The tanks being dry and collecting less moisture is a detail about their place in the system, but the reason for two delivery circuits is backup braking.
Why the other answers are wrong
- A. For efficiency — Efficiency is not the reason the handbook gives; the two circuits exist so one can still provide braking if the other fails.
- B. For fuel economy — Fuel economy is not mentioned as a reason for the dual-service tanks; the stated purpose is a safety backup if a circuit fails.
- D. For greater stopping power — Greater stopping power is not the stated reason; the second circuit is there to preserve brake function after a failure, not to increase stopping power.
Remember it
When you see primary and secondary, picture two separate air paths to the brakes, not one shared path.