I have a Pentair whisperflo pump and an fns plus 48 d.e. filter setup. The problem is that my returns completely lose flow and the pressure in the housing gets up to 25-30psi.
There are 3 valves on the suction side:
Ive rebuilt and sealed all 3 valves. I've also replaced the pump skimmer o-ring and its well lubrcated fearing of a suction side leak.
I also replaced my d.e. grids and added fresh de of course (4 designated scoops).
I don't know what else to do. The system runs flawlessly on recirculate. However on filter, it will gradually build up pressure in the d.e. housing and restrict the return flow. If I backwash for a couple minutes it will remedy the problem temporily. However I have to do this 4-5 times a day to keep it running properly.
Once the pressure builds up to 25-30psi I turn be pump off and open the bleed valve at the top of the tank and a bunch of air comes out and after a few minutes I'll hear a bunch of bubbling and then the water recedes out of the pump skimmer. When I do this, then turn the pump back on it does make the pressure drop. Only when I backwash does it drop the pressure back down to operating level.
I'm not sure if this is related but I've removed the filter housing lid a few times and every time I do the breather tube screen on the bleeder tube is caved in and clogged with debris.
Please help, I've been fighting with this non-stop for several weeks. We had a pool service for several years that we let go after they kept refusing to deal with this issue and I need to figure this out.