This tractor protection valve fits Mack and Navistar air brake systems and is built as a replacement for the original equipment. It closes automatically to isolate the trailer air lines from the tractor’s supply if trailer pressure drops sharply, such as in a breakaway or major leak. It ships as a single unit.Interchanges:25855062585506C914333-2585506C91Mack 4333-503139C91Navistar 503139503139C915396-KN34110LPV-3714FeaturesTractor protection valve for air brake systemsSold pack quantity: 1 eachTech SpecsSell pack: 1 Each