What Makes up the Emergency Brake System?
The emergency braking system activates the spring brakes when the vehicle loses air pressure in an air brake system. The spring brakes engage engage when the air pressure drops below 20 to 45 psi in the air storage tanks, thus stopping the vehicle. These brakes can sometimes be disengaged by the use of air located in a separate tank (if so equipped) in order to move the vehicle out of a potentially dangerous situation. These brakes can also be applied manually in the event of brake failure in vehicles equipped with a modulating valve. The modulating valve allows the driver to gradually apply the parking or spring brakes through the use of a lever in the cab in an effort to slow the truck down. When parking a semi truck with a modulating valve, the level must be placed in the “fully on” position and locked in place with a locking device.
