The tractor protection valve protect the tractors air supply from being depleted in the event of a trailer breakaway.
Must be used whenever two sources of air are used to operate a single device or system.
For CDL air brake test, the driver must know there are 2 in the system.
Used on some vehicles with dual air systems. This device provides a means of using the force of the spring brakes to assist in stopping a vehicle in an event of a failure in the rear (primary) air system.
Several relay valve throughout the air brake system reduce brake lag, thus allowing the brakes to apply faster.
Fills the trailer air tanks (reservoir) and applies and releases the trailer service brakes. The relay emergency valve also applies the trailer emergency brakes in the event of a trailer breakaway or normal disconnect.
Knowledge Test Question: In the event of a trailer break away, the relay emergency valve is required to apply the trailer service brakes for a minimum of 15 minutes.
To reduce application pressure to the steering axle by 50 % compared to the drive axle brakes, when required by reduced road conditions (rain, snow or ice).
The system consists of a dash switch with 2 positions:
Dry Road: 100% front wheel braking; in other words, all brakes apply equally.
Slippery Road: reduces braking force to the front brakes by (50%) when in the slippery position.