This relay valve is a replacement for Mack and Navistar air brake systems, sold one per unit. Mounted near the brake chambers, it applies and releases air on demand, cutting the lag that comes from routing everything back through the treadle valve. It falls under the Air Brake Parts, Valves category for easy identification at the counter.Interchanges:Navistar 3205416R91Mack 745-279180LRV-3682FeaturesRelay valveSold as one eachCategorized under Air Brake Parts, ValvesTech SpecsSell pack: 1 EACH