¼" VeeJet Strainer - 100 Mesh with check valve It requires 2 psi to push the sping move the ball away to allow the water to flow. This helps make carpet cleaning wand dripless on the dry stroke. If this is for a carpet cleaning wand, you would want them. Please make sure your wand has enough clearance on the inside of the back the jet manifold to accomidate the filter. Some wand manifold will crush the filter during installation.