When you test the system air-loss rate, the maximum acceptable air-loss rate per minute after the initial drop is ________ except for vehicles with two trailers.
- 28 kPa (4 psi) ✓
- 21 kPa (3 psi)
- 69 kPa (10 psi)
- 41 kPa (6 psi)
Answer: A. 28 kPa (4 psi)
After the initial pressure drop, air loss must not be more than 28 kPa (4 psi) per minute, except on vehicles with two trailers.
Why this is the answer
The Class 1 pre-trip inspection says to make a full brake application with the engine off and hold it for one minute. Once the pressure settles from that first drop, the loss must stay at or under 4 p.s.i. (27.6 kPa) per minute. The same passage gives a separate, higher allowance for vehicles pulling two trailers. So the general limit for a single unit or one trailer is the 4 p.s.i. figure, which is the value rounded to 28 kPa in the answer.
Why the other answers are wrong
- B. 21 kPa (3 psi) — Three p.s.i. per minute is the leakage figure quoted in the Class 3 pre-trip inspection passage, not the limit given for this check.
- C. 69 kPa (10 psi) — Ten p.s.i. per minute is not a leakage limit anywhere in the handbook passages provided.
- D. 41 kPa (6 psi) — Six p.s.i. per minute is the allowance that applies only when the vehicle has two trailers, which the question specifically excludes.
Remember it
Picture the two-trailer rig as the exception: it gets the bigger leak allowance, so the plain truck keeps the smaller 4 p.s.i. number.