288721N is a Bendix Supply Valve PP-7, a trailer brake supply valve. A valve of this type is a push-pull control that gives the driver in-cab control of the tractor protection system and works alongside the park control valve to keep parking and emergency braking coordinated between the tractor and the trailer. The knob is pushed in by hand and pops back out if supply air falls too low. It is a genuine Bendix part from Pro Gear and Transmission. Call us to confirm proper fit.A factory handling fee of $20.00 per unit is added at checkout.FeaturesBendix part number 288721NSupply Valve PP-7 model designationTrailer brake supply valvePush-pull in-cab control of the trailer supplyWorks with the park control valveGenuine Bendix part