Outfit your semi to be Ready for the Road Ahead™ with fast and reactive rear air brakes, with the Bendix R-12DC® 4 psi Air Brake Relay Valve. To quickly apply compressed air to the rear air brakes, this replacement component acts as a gateway between the service reservoir and the air brakes. Fashioned with a durable metal body to tolerate extreme pressures and regular use. FleetPride is your First Click in Heavy Duty®.