An exhaust treatment device for a combustion system is disclosed. The exhaust treatment device may have a housing, and an injector disposed within the housing to deliver an injection fluid into a flow of exhaust. The exhaust treatment device may also have at least one fluid supply passage that is disposed within the housing and being in fluid communication with the injector to supply the injector with injection fluid. The exhaust treatment device may further have at least one purge passage disposed within the housing and in fluid communication with the injector to supply the injector with a purge fluid. The exhaust treatment device may additionally have a first valve element that is mounted to the housing and disposed at an entrance of the at least one purge passage The first valve element may be configured to provide a unidirectional flow of purge fluid to the at least one purge passage.