Outfit your semi to be Ready for the Road Ahead with fast and reactive rear air brakes, with the Sealco 4-Port 4.5 psi Emergency Relay Valve. Thanks to its fixed location between the rear air brakes and the service reservoir, this replacement component is able to quickly apply compressed air to actuate the air brakes. Crafted with a rugged metal body to withstand extreme pressures and daily use. FleetPride is your First Click in Heavy Duty .