Ensure your semi is Ready for the Road Ahead™ with fast and reactive rear air brakes, with the Bendix R-12® 4 psi Air Brake Relay Valve. By positioning itself between the service reservoir and the rear air brakes, this replacement component is able to quickly release compressed air and actuate the air brakes. Built with a solid metal body to tolerate extreme pressures and daily use. FleetPride is your First Click in Heavy Duty®.