Ensure your semi truck is Ready for the Road Ahead with , with the OTR BP-R1 Type 4 psi Bobtail Relay Pressure Proportioning Valve. With a sophisticated design, this replacement valve is able to evenly distribute the brake pressure between the front and back wheels, providing enhanced control when slowing or stopping. Crafted with top-tier materials to withstand harsh operating conditions. FleetPride is your First Click in Heavy Duty .