The foot (treadle) valve
- should be held halfway down during normal driving.
- controls the air pressure applied to the brakes. ✓
- is connected to the brake chambers by rods and linkages.
- controls the speed of the air compressor.
Answer: B. controls the air pressure applied to the brakes.
The foot (treadle) valve controls the air pressure applied to the brakes.
Why this is the answer
The handbook describes the foot control valve as the way the truck brakes apply the trailer brakes in a combination vehicle. It also says the pressure applied to both the trailer and tractor brakes is the same. That points to the foot valve as the control for brake air pressure, not a device for setting compressor speed or a mechanical linkage. The passage supports the bank answer indirectly rather than with a single direct definition.
Why the other answers are wrong
- A. should be held halfway down during normal driving. — The handbook describes applying steady pressure at the start of a stop and easing off as the vehicle slows, not holding the valve halfway down during normal driving.
- C. is connected to the brake chambers by rods and linkages. — The passages do not mention rods or linkages connecting the foot valve to the brake chambers; they describe brake application through air pressure.
- D. controls the speed of the air compressor. — Nothing in the passages says the foot valve controls the speed of the air compressor; it is tied to applying brake pressure.
Remember it
Think of your foot as setting the air pressure sent to the brakes, not as holding a halfway position.
Official handbook: Official MTO Truck Handbook, Use of brakes