Upon driver releasing the treadle in an air brake system, to where does the air get directed?
- Into the compressor
- Back into the reservoir
- Into the atmosphere ✓
- Through the brake drums
Answer: C. Into the atmosphere
When the driver releases the treadle, the air is directed into the atmosphere.
Why this is the answer
The handbook says that when you let up on the foot valve, the application air in the brake chambers is exhausted through the valve’s exhaust ports into the atmosphere. Releasing the treadle opens an exhaust port, and the air that had been applied to the chambers escapes outside. The return springs then bring the pushrods and brake parts back to the released position. That is why the correct choice is the one describing air going into the atmosphere, not staying in the system.
Why the other answers are wrong
- A. Into the compressor — Air is not sent into the compressor; the compressor takes in outside air and pressurizes it for storage in a supply reservoir.
- B. Back into the reservoir — The release air is not sent back into the reservoir; the handbook says it exhausts through the foot valve’s exhaust ports to the atmosphere.
- D. Through the brake drums — Air is not routed through the brake drums; the passages say the brake linings retract away from the drums when pressure is released.
Remember it
Picture letting up on the treadle as opening a vent: the applied air leaves the brake chambers for the outside.