Product Details: Ensure your semi is Ready for the Road Ahead™ with fast and reactive rear air brakes, with the Prima Brake R-12 Type 5.5 psi Relay Valve. This replacement component allows for the immediate application of compressed air to the rear air brakes, by acting as a gateway between the service reservoir and the brakes. Engineered with a durable metal body to withstand extreme pressures and consistent use. <br/><br/>FleetPride is your First Click in Heavy Duty®.