The trailer air supply control should pop out when the air pressure falls into the pressure range of:

Question

Accepted Answer

B: 20 to 45 psi.. Regulations dictate that a visible low air pressure warning indicator be activated and placed in full view of the operator when the pressure in the air supply system falls lower than 75 to 55 psi. Once the pressure drops even lower (45 to 20 psi) then the trailer air supply control (aka tractor protection valve) should pop out so that air is isolated and remains in the tractor air brake system.

The trailer air supply control should pop out when the air pressure falls into the pressure range of:

North Carolina CDL Doubles/Triples Test Info