This air brake relay valve is designed for Mack heavy-duty truck applications and is sold as a single unit. Mounted in the air brake system, it applies or releases air to the brake chambers on command, positioned closer to the chambers than the treadle valve to cut down on lag. It is a replacement for use in Mack air brake systems.Interchanges:Mack 5396-KN28510LRV-3612FeaturesAir brake relay valveSold as a single unit (1 EACH)Fits within Air Brake Parts product groupTech SpecsSell Pack: 1 EACHProduct Group: Air Brake Parts