I have a 10 year old 30,000 gal in ground liner pool with a hayward de4820 DE filter and 1.5hp hayward pump. I started getting DE back in the pool in small amounts about 6 years ago. I was having issues with spider gasket in the valve deteriorating rapidly- I'd open the valve up and it would always be detached in the area where the upper part of the valve was not touching when in the "filtration" position during normal operation. I thought that was the issue but replacing the gasket and the pressure spring in the valve reduced but did not eliminate the DE problem. Grids, manifold and internal elbow in the filter were perfect. I basically had to let my skimmer connected vacuum run continuously to keep the bottom clean.
This year I finally got tired of that and got an electric robotic vac and even though I could find no problems inside the filter replaced all the grids and manifold, and eliminated the valve by plumbing the pump output directly to the filter. (I usually remove the filter assembly to clean the DE off anyway and figured the elimination of the valve as a potential trouble point outweighed the backwash functionality) I also put a check valve in between the pump outlet and filter inlet and double checked to make sure the internal elbow between the manifold and filter inlet was good, and there is a new o ring in the manifold to internal inlet tube. Result of all this work is that I'm still getting the same amount of DE back in the pool. I've just done a manual vac job and removed and cleaned the filter assy again and figure I'd give it one more vacuum in a few days before I scrap the DE filter and go with a cartridge system if the bottom of the pool is not DE free. Nobody at any of the pool places can help me other than to insist its a torn grid or cracked manifold or valve issue, and these have all been addressed. If anybody here has any ideas I'd love to hear...
additional info: pressure without DE is 13psi, with the specified 6lbs of DE 15-16 psi. Plumbing is 1-1/2", there are 2 outlets, one skimmer, the pump is 1.5hp 83gpm at 20'head and a DE4820 has 48 sq ft of filter area. After cleaning the filters I turn on the pump, bleed the air from the filter housing, then add DE thru the skimmer. When taking apart the filter I can see that the DE is indeed evenly distributed everywhere on the grids. I find it hard to believe that I'm still having this issue, unless perhaps I'm getting DE with some proportion of undersized grains that the filter is unable to catch that settle to the bottom of the pool. If this is the issue I would expect to see complaints on this forum and others but I don't...
tom