a nut shell filter allows the shell filter media to be scrubbed without being removed from the filter vessel . in order to protect the vessel from pressure surges which can occur during the scrubbing cycle , pressure applied during the beginning of the scrubbing cycle is contained within a scrubber tube such that the filter vessel is not subjected to pressure surges which occur at the beginning of the scrubbing cycle . the scrubber tube and scrubber filter tube may either be disposed within the filter vessel or outside of the filter vessel .