Should you pump (keep pressing and releasing) air brakes?
- Yes, it compensates for poor adjustment of the brakes.
- Yes, it helps build up air pressure.
- No, it causes loss of air pressure. ✓
- Yes, this procedure is recommended for highway driving.
Answer: C. No, it causes loss of air pressure.
No — pumping the air brakes causes a loss of air pressure.
Why this is the answer
The handbook says the brake pedal controls air pressure sent to the service brakes, and pressing it draws compressed air from the primary and secondary tanks. When you pump, you press and release repeatedly, so you keep drawing air from the tanks instead of holding a steady application. The air-loss test also calls for holding the pedal fully applied and watching the gauges, not fanning the pedal. The passages support that pumping uses up air; they do not present it as a repair or a pressure-building method.
Why the other answers are wrong
- A. Yes, it compensates for poor adjustment of the brakes. — Nothing in the passages connects pumping with brake adjustment, and the handbook does not describe pumping as a way to make up for poor adjustment.
- B. Yes, it helps build up air pressure. — Air pressure is built by the compressor under the governor's control; pressing the brake pedal delivers air to the brakes and draws it from the tanks, so it does not build pressure.
- D. Yes, this procedure is recommended for highway driving. — The passages describe a steady fully applied pedal for the air-loss test, not pumping as a highway driving procedure.
Remember it
Remember: the pedal spends tank air; the compressor makes air. Don't fan the pedal to try to help the system.