Regularly replacing the sleeves on your filter will help to prolong the life of your carbon filter by keeping it from getting clogged up with larger particulate, and ensuring it's working efficiently.
As a rule of thumb - if it looks dirty then it needs replacing.
The Rhino Pro Replacement Pre-filter Dust Sleeve is an exact replacement for the Dust Sleeve provided with the Rhino Pro Carbon Filter. The Dust Sleeve fits over the Rhino Pro Carbon Filter and removes dust and large particles from the air before they enter the main filter drum containing the activated carbon. This prevents the main filter part from becoming clogged which reduces the air flow and the filter's efficiency. The replacement dust sleeve is useful for replacing a worn out, clogged or damaged original dust sleeve to maintain the efficiency of your Rhino Pro Filter.