I have a nice Jandy CL-580 cartridge filter for my pool. It uses 4 standard replaceable filters in a canister. The whole thing is properly plumbed, that is, the intake goes the correct spot, as does the output. The pressure gauge on the top registers pressure in a strange way. Normally when I clean the filter, and replace the cartridges, the pressure runs about 12 PSI on the high power of my pool pump. Now, as the cartridges get clogged, the pressure goes down, not up! Based on that you would think that somehow the pressure gauge stuck on top of the canister would somehow be on the output side, so that when the filters get clogged, the output goes down. I have looked the situation over completely, and the pressure gauge is on the correct side of the equation. That is, the water comes in the inlet from the pump, fills the canister, and is pushed through the filters into the manifold where it is expelled to the pool side. So, I cannot figure out why this is. Now, I have no problem filtering, and all works fine, but what am I missing here???