Relay valves provide for quicker application of the brakes by keeping an air charge away from the back brakes, tractor, or trailer.
The spring brakes would lose their retention charge and apply emergency force, locking the trailer tires, if the supply line burst. The tractor would be shielded from a complete loss of air pressure by the tractor protection valve.
At 45–20 PSI, the main reservoir pressure should trigger an emergency application of the spring brakes.
When using the hand pull method, a cool running temperature and about 1/2 inch of push rod travel are required for efficient braking.
At 60 PSI, the low pressure warning device—which typically included a buzzer, red light, or drop-down indicator—should activate. Check your sensors if it doesn't.
One reservoir manages the rear brakes and another controls the front brakes in a dual circuit system. Even with one reservoir depleted, the car would still be able to brake, but with less force.
The compressed air required to run an air brake system is produced by an under-hood compressor.
Applying a service brake while the spring brakes are still engaged is known as compounding the brakes. High levels of stress are placed on the diaphragms and slack adjusters as a result, which may lead to premature component wear.
The most frequent range is 105-125 PSI, while other systems operate at 85-105 PSI.
Air cannot return from the reservoirs to the compressor thanks to a one-way check valve. Usually, this valve is spring-loaded.
Unless you applied the service brake, which would release air from the reservoirs, nothing would happen. However, the tractor protection valve would prevent complete loss, allowing the tractor to continue to operate as a brake.
