This small wire filter sits directly underneath your vacuum motor. It is a second line of defence to stop dust getting into the motor. You dont have to replace this filter but it may require cleaning if your main filter has fallen down or is too full to do its job.
If you are experiencing poor suction from your ducted vacuum that may mean the secondary filter is blocked. If this is the case give us a call today and organise a service call to get your system cleaned and running at 100% again.