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What does pressing the brake pedal actually control in an air brake system?
- A.It directly pushes the brake shoes by mechanical rod
- B.It pumps air from the tanks back to the compressor
- C.It switches the spring brakes on and off
- D.It meters how much air pressure is sent to the brake chambers, so pedal force controls braking force
Correct answer
D. It meters how much air pressure is sent to the brake chambers, so pedal force controls braking force
Why
The treadle valve works like a faucet for air: the harder you press, the more pressure reaches the chambers and the harder the brakes apply. That is also why a light, steady squeeze uses less air than repeated hard stabs on a long grade.
Manual topic: Air Brakes - Service Brakes · From the General Knowledge practice bank (GK-128).