Shop-Vac Vacuum Relief Valve

thingiverse

This is a vacuum relief valve that can be screwed in place of the drain at the bottom of a shop-vac. This does not require any modification to the vacuum, and you can quickly reverse it just by screwing the original cap back in place. This probably works best with a bag, although I carefully designed it to not extend into the body of the vacuum, so it may work ok without one.This requires a 6mm bolt and nut and a spring of some sort.