Pond Boss Forums AERATION Systems questions Black filters on rotary Vain compressor?

The internal "fuzzy" filter on the outlet port is to catch or trap and collect the carbon dust from abrasion of the vanes before it leaves in the air out the pump. If you have a good external filter the internal INTAKE filter will stay clean whereas the internal OUTLET filter will collect small amounts of carbon dust over time. I usually (annually) just lightly tap the dust out of it and replace it. Rebuild kits contain new internal filters, O rings, vanes and a new head gasket. Engineers at GAST tell me the carbon dust acts as a lubricant for the vanes and rotor.