Get your semi Ready for the Road Ahead with fast and reactive rear air brakes, with the Bendix R-12DC 4 psi Air Brake Relay Valve. With a fixed location between the rear air brakes and the service reservoir, this replacement component allows for the immediate application of compressed air to the brakes. Manufactured with a solid metal body to endure extreme pressures and consistent use. FleetPride is your First Click in Heavy Duty .