Hunt for the DE leak in my FNS Plus Filter: Solved

[Brushman]

A couple of weeks ago I posted for help in the VIP Lounge for this problem. (Thanks HermanTX.) Since I finally solved my DE problem today, I wanted to post a summary here with some pictures. I didn't find a ton of information when I first started digging around for help with a DE leak, so I hope this will help someone else. I've got a seven year old pool equipped with a 60 sf Pentair FNS Plus DE Filter. It has always worked great, but this year I noticed a little bit of DE was being ejected from the return lines. It was time for a deep clean anyway, so took the filter apart the first chance I got. The grids and covers were all original, so at seven years old, a tear in one of those was my first suspect. I disassembled and cleaned each grid, and I could tell right away that a few of them were showing their age, with small cracks now showing in a handful of corners. I did not see an obvious tear anywhere, but I knew that after 7 years they were due for replacement, so I didn't spend a ton of time trying to find the kind of small rip that would be enough to cause my problem. Instead I quit hunting, bought a new set of grids and covers, carefully reassembled everything, cleaned the inside of filter, put a new screen "hat" on the air bleed assembly, replaced and lubed the standpipe gasket, carefully put my reassembled filter assembly back on the standpipe, cleaned and lubed the main housing O-Ring, and buttoned it all back up. I almost hurt my shoulder patting myself on the back for doing such an excellent job. The next morning, I went outside still feeling like the smartest pool guy in town. Then I looked down and realized my DE flow was exactly the same. There were hurricanes in the forecast so there was nothing I could do about it until today, when I finally had time for Round Two of my Great DE Hunt.

 

[Brushman]

At least the filter was cleaner today, which made it all a little easier. Put the filter back in maintenance mode, opened the vent and bled the water out through the backwash (again), and took the filter assembly out again. I figured I was either looking for a defect in one of my replacement grids and covers, or possibly a subtle crack in the manifold which had escaped detection during my first go around. Here's a picture of the grid assembly before I cleaned it off. There's a clue in there.

 

[Brushman]

Or at least I hoped it was a clue -- I was interested in that little drift of DE around the air bleed assembly tube. That's the little thing with the screen mesh hat on top. I took some pictures and then cleaned everything off, looking all around for cracks. Nothing. I pulled the air bleed assembly tube out and looked around. Nothing. I looked everywhere. Nothing. I went back and checked the standpipe (again) for a crack. Nothing. I began to think my most unlikely suspect, a defect in the multi-port valve, might actually be the problem. Or maybe one of my brand new covered grids had a defect. Ugh. Those things were possible but seemed less likely, so I kept looking. I looked straight up inside the big circular opening in the manifold, where the standpipe goes in. And that's when I saw something I shouldn't have seen. A tiny sliver of sunlight. And it was right underneath where the little tell tale pile of DE had been sitting. So I pulled the air bleed assembly and checked again. Using my fingernail I found a groove where there shouldn't have been one. Problem solved! Very subtle cracks that were basically inside where the air bleed assembly tube slides in. Here's a closeup picture. Once you know what you're looking for, and where, they seem almost obvious. But they weren't to me. It was my first DE hunt and I had missed the defect the first two times I went looking for it. I thought seeing pictures of what was causing the problem might help someone else. Hope it does!