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Why should the trailer hand valve not be used to hold a parked trailer or combination?
- A.Hand valves can leak down and release, and relying on one can also promote skidding if used while moving; parking must use the spring (parking) brakes
- B.Hand valves apply the spring brakes permanently
- C.Parking with the hand valve drains the fuel system
- D.It is forbidden to touch the hand valve for any reason
Correct answer
A. Hand valves can leak down and release, and relying on one can also promote skidding if used while moving; parking must use the spring (parking) brakes
Why
A hand valve holds brakes only while air pressure is maintained through it, which is not a fail-safe park condition. Spring brakes apply mechanically when air is removed, which is what parking security requires.
Manual topic: Air Brakes - Trailer Air Brakes · From the Air Brakes practice bank (AB-239).