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
Edited and Illustrated by Charles Miller
From Fine Homebuilding #237
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seems like shop vacs used to come with a foam sleeve
Indeed they did come with a cheap foam filter... They clog to fast and were efficient only if you cleaned them often. The newer pleated fabric filters are way better because they have 10 times more surface to breathe. This means a lot more air flow and a longer run before requiring cleaning. I clean them also with my air compressor... Its dirty because it can hold a lot more dust because of the longer run.
This kind of defeats the purpose of a pleated filter, which has more surface area than a foam filter. A better way of keeping your pleated filters from filling up and extending maximum suction time would be to use one of the few mini dust cyclones that can be attached to your vacuum. I fashioned a "Dust Deputy" by Oneida to fit above my shop vac so as to save floor space and maximize portability. Works fantastic and I can vacuum all day straight and not have to clean out the filter.