An injector for injecting a reagent includes an axially translatable valve member positioned within a housing. A flux sleeve is surrounded by a coil of an electromagnet. A pole piece defines a return passageway for reagent to flow. A filter surrounds the pole piece and includes a cage and a mesh fixed to the cage. The cage includes a deformable first seal biasedly engaging an outer surface of the pole piece. The cage includes a second seal biasedly engaging the housing. The first and second seals define a closed volume such that all of the reagent flowing through the injector passes through the mesh.