The Bendix unloader valve refer to two distinct types of air system management components: internal unloader mechanism and external discharge line unloader (DLU) valve. The internal unloader mechanism is an assembly of pistons and plungers located in the cylinder head. Some heavy-duty systems use a Discharge Line Unloader (DLU) configuration where the compressor pumps continuously and delivery is managed by an external valve. The Bendix+ DRO Unloader Valve is the external valve mounted in the discharge line between the compressor and the air dryer.