The pleated filter on a shop vacuum can get thoroughly clogged. Cleaning one of those filters, which I do with compressed air and a small screwdriver, is a dirty and time-consuming job.
Years ago, I got tired of this and started putting a prefilter over the regular filter. At Grainger or any HVAC supply house, you can buy 1⁄4-in.-thick trim-to-fit foam filters in sheets or rolls (Grainger’s is #1W755). As shown in the drawing at right, I cut a piece to cover the filter and seal the overlapped seam with PVC glue. I begin by wrapping the foam around the filter, noting the cutlines and overlap, then pulling it off the filter. After trimming the foam, I glue it into a sleeve that is a little smaller than my marks indicate for a snug fit. When it’s dirty, I just pull it off and shake it clean. If it’s really clogged, I use compressed air or even wash it in water. This keeps all but the smallest particles out of the standard filter. You can use this idea for lots of other filters.
Joseph Kaye, Phenix, VA