Upgrade your MACK truck's air brake system with the 8235-RKN31003 Air Brake Pressure Protection Valve - KN31003, designed to ensure optimal performance and safety. Find it at bboverstock-salvage.com. Why Pay More for essential components? At BB Overstock & Salvage, we value your time, which is why most orders ship the same day, and we ship 6 days a week. As a small, family-run business, we take pride in offering top-quality parts at competitive prices while maintaining exceptional customer service.